12:1 Input Quarter-Brick DC-DC Converters Target Railway Systems

RECOM has expanded its railway portfolio with two 40 W and 60 W DC/DC converter series in quarter-brick packages with an ultra-wide input voltage range from 14 VDC to 160 VDC..The 12:1 input voltage range of RECOM’s RP40Q-RUW and RP60Q-RUW series covers all input voltages from nominal 24 VDC up to 110 VDC in a single product (including EN50155 transients).

These quarter-brick DC/DC converters are designed for railway rolling stock and high voltage battery applications and offer basic isolation with regulated 5 V, 12 V, 15 V, 24 V or 48 VDC outputs, including sense and trim pins. They have a consistently high efficiency over the entire input voltage range and an operating temperature range from -40°C up to +85°C (+68°C for the RP60Q-RUW) at full load without forced air cooling.

An optional heat sink allows these converters to provide full load up to +90°C and +77°C respectively. The case is fitted with threaded inserts for secure mounting in high shock and vibration environments. The converters are CE marked, EN50155 and EN45545-2 certified and come with a three-year warranty. Samples and OEM pricing are available from all authorized distributors or directly from RECOM.

RECOM | www.recom-power.com

Wireless Charging

Electric Field of Dreams

The concept of wireless charging can be traced all the way back to Nikola Tesla. Here, Jeff examines the background and principles involved in charging devices today without wires, and takes a hands-on dive into the technology.

By Jeff Bachiochi

________________________________________________________

Nikola Tesla is the recognized inventor of the brushless AC induction motor, radio, fluorescent lighting, the capacitor discharge ignition system for automobile engines and more. His AC power (with Westinghouse) beat out Thomas Edison’s DC power in the bid for the electrification of America. DC transmission is limited to miles due to its relatively low voltage and its transmission line loses. Thanks to the advent of the transformer, AC can be manipulated allowing higher voltages and higher efficiency power transmission. Today’s research in superconducting cable may be challenging these concepts—but that’s a story for another time.

Tesla wanted to provide a method of broadcasting electrical energy without wires. The Wardenclyffe Tower Facility on Long Island Sound was to be used for broadcasting both wireless communications and the transmission of wireless power. Tesla even viewed his research on power transmission as more important than its use as a method for communications. Unfortunately, Nikola was never able to make his vision a reality.
We think of Guglielmo Marconi as being the father of radio for his development of Marconi’s law and a radio telegraph system. He was able to obtain a patent for the radio using some of Tesla’s own ideas. It’s interesting to note that after Tesla’s death in 1946, the U.S. Supreme Court invalidated the Marconi patent because the fundamental radio circuit had been anticipated by Tesla. Again, not the direction of this article.
It was likely that Nikola’s work in far-field power transmission had not been fruitful due to propagation losses (inverse square law). Even today’s work on beam-formed, far-field transmissions are marginally successful. Transformers are successful because they operate in the near field. The close proximity between the primary and secondary coil and a well-designed magnetic energy path result in low energy losses in transformers.

Modern Wireless Charging
Today’s wireless charging systems for our portable devices are based on transformer operation. However, the primary and secondary coils are not in physical contact yet still transfer energy Figure 1. Efforts to maximize the magnetic field’s coupling exist, but this less-than-ideal coupling reduces the efficiency of the transfer—50% to 70% efficient. There are basically two methodologies today: inductive (tight) coupling (near field) and resonant inductive (loose) coupling (mid field). The resonant circuit allows an equivalent power to be transferred at a slightly greater distance.

Figure 1
The device is considered near-field (closely coupled) when the distance between the coils is less than the coils diameter. The mid-field device’s distance exceeds the coils diameter and relies on resonance to improve its power transfer.

Wireless efforts are in total flux with at least three organizations jockeying for position: The Wireless Power Consortium (WPC, induction), the Alliance for Wireless Power (A4WP, resonant) and Power Matters Alliance (PMA, induction). Interestingly, after WPC announced its plans to widen their specs to include resonant technologies, A4WP and PMA merged to become the AirFuel Alliance and now cover both technologies as well.

Beyond induction type, the biggest differences between the technologies is in control communication. Control of the charging process requires communications between transmitters and receivers. Induction technology uses in-band modulation of the RF signal to send and receive communications. Resonant induction technology uses Bluetooth for out-of-band communications. This makes the transmitter/receiver pair simpler but adds the complexity of Bluetooth. Since many receiving devices already have Bluetooth, this may be moot.

The Qi Standard
The WPC has coined the term Qi for their standard. If you search the web for wireless charging, this term pops up all over the place. This is not to say the AirFuel’s standard isn’t available—it seems to be a difference in promotional strategies. AirFuel has invested in getting their receivers into devices and their transmitters installed in public places. And while Qi receivers are also going into devices, their transmitters seem to be aimed at the individual. That means easy access to both Qi transmitters and receivers.
You can get the V1.2.2 specifications for the Qi standard from the WPC website. The current version (1.2.3) is available only to members now but should be public shortly. The two documents I received were “Reference Designs” and “Interface Definitions” for Power Class 0 specifications.

Power Class 0 aims to deliver up to 5 W of energy wirelessly via magnetic induction. This is accomplished by applying a fixed RF signal—generally in the 140 kHz range—into an inductive load (transformer primary). This is much like providing motor control using a half or full bridge, with the (transmitting) coil as the load instead of a motor.
Referring back to Figure 1, a receiver uses a similar coil (the transformer secondary). This coil supplies rectification circuitry with the voltage/current needed to power the receiver. The receiver can vary its load, which modulates the burden on the transmitting coil. Back at the transmitter, a change in the primary’s current can indicate when the secondary’s load is in range. Initially the transmitters remain relatively inactive, except for a periodic “ping” to look for a receiver. A normal ping will occur every
500 ms and last about 70 ms (Photo 1). Once in range the receiver gets secondary current and can self-power. During the last 50 ms of a ping, a receiver has a chance to communicate by modulating its load at 2 kHz rate (Photo 2). There are presently 16 messages it can choose to send.

Photo 1
This oscilloscope screenshot shows the “ping” transmissions of a wireless transmitter with no receiver in range.

Photo 2
Here we see a receiver sending a packet by modulating its load during the transmitter’s RF transmission.

Each message has four parts: a preamble, header, message and checksum. The preamble consists of from 11 to 25 “1” wake-up bits. The header is a 1-byte command value. The message length is fixed for each command, presently 1 to 8 bytes. The checksum is a 1-byte sum of the header and message bytes. All bytes in the header, message and checksum have an 11-bit asynchronous format consisting of a start bit (0), data bits (for example Command, LSB first), odd parity bit (OP) and stop bit (1). Each bit is sent using bi-phase encoding. Each bit begins with a state change in sync with its 2 kHz clock. The value of a bit is “0” when its logic states does not change during a 2 kHz clock period. If the state does change within that period, then the bit is a “1”.

The receiver has control over the transmitter. It initiates communication to send information and request power transfer. Back in Photo 2 you can see a Control Error Packet with a Header=0x03 and data=0x00. The signed value of the data indicates any difference between the requested and received current level.

While the receiver is in charge (ha!), the transmitter can acknowledge requests with 1 of 3 responses: ACK (accept), NAK (deny), or ND (invalid). Responses have no packet per se, but are merely a Frequency-shift keying (FSK) modulated pattern of 0s, 1s or alternating 0s and 1s. The receiver can request the depth of the FSK modulation from a list of choices between +/- 30 to 282 ns. The depth is defined as the difference in ns between the 1/Fop (operating frequency) and 1/Fmod (modulation frequency). The format is again bi-phase encoding in sync with the RF frequency. All bits begin with a change in modulation frequency. A “1” bit is indicated by a change in frequency after 256 cycles, while a ‘”0” bit has no change until the beginning of the next bit time. Responses are therefore easy for a receiver to demodulate.

So, communication is AM back-scatter from the receiver and FM on the base RF from the transmitter. The present specification defines three packets that can be sent by a transmitter in addition to the ACK, NAK and ND. These are informational and are formatted like the receiver packets, less the preamble.

System Control
From the transmitters point of view, it has 4 basic states: ping, ID, power transfer and selection. The transmitter is idle while in the ping state. Without some communication from a receiver, the transmitter will never do anything but ping. Once communication begins the receiver attempts to identify itself and become configured, at which point the transmitter can start power transfer. The transmitter will continue monitoring its feedback and change states when necessary. For instance, if communication is lost, it must cancel the power transfer state and begin to ping. The ability to detect foreign objects (FOD) is required for any system that can exceed 5W of power transfer. This parameter adds an additional 3 states to the basic 4 states: negotiation, calibration and renegotiation. When using FOD the negotiation state is required to complete identification, configuration and calibration. Calibration allows the transmitter to fine tune its ability to FOD. During the power transfer state, the receiver may wish to adjust its configuration. As long as no requests violate operational parameters, the power transfer state can continue. Otherwise the selection state will redirect further action. You can see how this works in the state diagram in Figure 2.

Figure 2
This is a general state diagram of the Qi standard for wireless chargers. Note two potential paths based whether or not foreign object detection is supported (required for greater than 5 W).

From the receiver’s point of view, it could be in an unpowered (dead) state prior to entering the transmitter’s field. Once within range, the short ping from a transmitter is sufficient to charge up its capacitive supply and begin its application programming. Its first order of business is to look for a legal ping, so it can properly time its first request 40ms after the beginning of a ping. The first packet is a signal strength measurement, some indication of transmitted energy. This is sufficient for the transmitter to enter the identification and configuration state by extending its RF timing and look for additional packets from the receiver. The receiver must now identify itself—version, manufacturer and whether or not it accepts the FOD extensions. A configuration packet will transfer its requirements as well as the optional packets it should expect. The transmitter digests all this data and will determined, based on the receiver’s ability to accept FOD extensions, whether it will proceed directly to the power transfer state or enter the negotiation state.

Packets must have a minimum of 7 ms silent period between each. The values sent in the configuration packet denote an official power contract between the transmitter and receiver. When the receiver doesn’t accept FOD extensions, it is this contract that the transmitter will abide by once it enters the power transfer state. If FOD extensions are enabled, it enters the negotiation state in an attempt to change the contract and provide higher power. The transmitter’s response lets the receiver know when a request to change a parameter is acceptable. This way both receiver and transmitter agree on the power contract it will use when negotiations are closed.

Once negotiations have ended, the calibration state is entered. The calibration consists of multiple packets containing received power values measured by the receiver while it enables and disables its load (maximum and minimum power requirements). This provides the transmitter with some real use values so it can better determine FOD.
During the power transfer (PT) state, the receiver must send a control error packet every 250 ms that the transmitter uses to determine its operating (PID) parameters. Meanwhile, received power packets are sent every 1,500 ms. Without this feedback, the transmitter will drop out of the PT state. Other packets can affect the PT state as well—most notably an end power packet. This may be due to a full charge or other safety issue and the transmitter drops out of the PT state. At this point a receiver can cease communication and while the transmitter will begin pinging, the receiver can rest indefinitely.

Sense, Configure, Charge
I’ve found that the Qi receivers with micro USB connectors make it easy to add wireless charging to your phone or tablet. One of these fits inside my Motorola phone with only the smallest bump of the connector on the outside. My Amazon Fire is not so lucky. It had to stay on the outside (Photo 3).

Photo 3
Shown on the left, the Amazon Fire required me to add the Qi receiver to the outside. It’s covered with a very large band-aid. On the right, my Motorola phone had room inside. The only clue is the receiver’s minimally obtrusive micro USB connector.

Adafruit has a module available that has no connector and is not enclosed in a skin (Photo 4). You can see in that photo that a receiver requires very few external components. This one uses a Texas Instruments bq51013B, which is less than $4. One advantage to choosing this device is the non-BGA version which is appealing to the DIYer that wants to hand solder the device onto a PCB.

Photo 4
You can see how few components are required on the Adafruit Qi wireless receiver shown here on a wireless transmitter. The voltmeter shows a voltage output of 4.98 V.

I suggest that you use high strand, flexible wires when making connections to this because a stiff wire can cause undue stress on flexible circuitry. I want to use this wireless charge receiver to keep some of my robots charged. To do this, the robot has to ride over the top of a transmitter. The receiver would then recharge the on-board battery or batteries. I’ve chosen to use Li-ion batteries because they have a high power-to-weight ratio. They also have a relatively flat discharge curve. Unfortunately, a single cell 3.7-V Li-ion battery is not sufficient to power most motors. Therefore, multiple cells must be used.

When multiple cells are in series the charging becomes an issue because the cells should be charged using a balanced charger to prevent charge imbalance. Charging cells in series as a group cannot prevent the over/under charging of individual cells. This means one of two approaches: Use a single cell and use a boost power converter to obtain your necessary voltage, or use a more complicated multi-cell, balanced charger with a boost converter between the wireless receiver and the charger’s input.
Upon contemplating the pros and cons of each method, I’ve decided to use a modular approach by treating each battery as a separate entity. The simplest charging IC I could find was STMicroelectronics’ STC4054. This is a TSOT23-5L (5-pin) device that requires only one external component to set the charging rate. This is important because some chargers will allow very high currents and I will be sharing the current for all chargers via one wireless receiver. While these can handle 1 A, if I want to say, charge four Li-ion batteries in series I need to limit each charging circuit to 250 mA (250 X 4 = 1,000) or I run the risk of the wireless receiver becoming overloaded and everything will shut down.

The STC4054 has a charging voltage of 4.2 V using the maximum of whatever current you set by the resistor you choose from the PROG pin to ground using the following formula:

rearranging we get…

A minimum VCC of 4.25 V is sufficient to sustain a complete charge cycle. Here is a breakdown of the whole charge cycle: If the battery voltage is below 2.9 V it will be trickle charged at 1/10 of IBAT. Once it reaches 2.9 V it enters the constant current mode charging at IBAT. Once it reaches 4.2 V it switches to constant voltage mode to prevent over charging. The cycle ends when the current drops to less than 1/10 of IBAT. Should the battery voltage fall below 4.05 V, a charging cycle will begin to maintain the battery capacity to a value higher than 80%.

The STC4054 is thermally protected by reducing the charging current should the temperature approach 120°C. The package leads are the main heat conductors from the die, so sufficient copper areas on the PCB will help with heat radiation. The device will max at 800 mA, but is spec’d to handle 500 mA at 50°C. You can expect stability without additional compensation unless you have long leads to the battery. A 1 µF to 4.7 µF capacitor can be added to the BAT connection if necessary.

The CHRG pin is an open-collector output which can be monitored to indicate when the IC is in the charging state. It will pull down an LED if you wish a visual status indicator. This IC will cost you about $1.50. With no voltage applied to the IC, it will go into a power down mode with a drain of only 17 µA on the battery.

Now this circuit takes care of charging a single battery, and we might have up to four in series. It’s the series part that is the problem because only the first can have a reference to ground. Since the wireless receiver is designed to produce a 5 V output, this is easily connected to the first charging circuit. We could try and get fancy with a boost converter to get a 20 V output to feed the four chargers with their inputs in series, but this has all kinds of bad karma associated with it. Fortunately, there is a rather inexpensive solution: Use isolated DC-DC converter modules. All converter inputs are in parallel on the wireless chargers output. Each of the converters’ outputs can be tied to a separate charging circuit. Since each of the converters’ outputs are isolated from its inputs, there is no reference to ground—the minus output of the wireless receiver). That means they can then be used to charge batteries which are connected in series.

The circuit given in Figure 3 shows four changing circuits—each (potentially) using its own isolated 5 VDC to 5 VDC converter. These are available in 1 W to 3 W SIP-style packages and cost from $3 to $10 each. Modules with high current (greater than 3W) are available, but the package style changes to DIP. Their inputs are in parallel with a connector meant to go to the wireless charging receiver. There are a lot of jumpers used to select how the outputs of each charging circuit are to be connected to output connectors. Each charger can charge one Li-ion battery using a standard two-pin 1S1P (one series cell, one parallel cell) connector. Or you can jumper them in series, which uses the standard connectors for 2S1P, 3S1P and 4S1P (series cells).

Figure 3
This schematic shows four Li-ion cell charging circuits using the STC4054. The input to each IC can come from an optional isolated source when using a DC-DC converter from RECOM. If each of the charging circuits are isolated, they can be applied to separate Li-ion cells in series.

You’ll note that multi cell Li-ion battery packs usually come with two connectors—one for use and one for charging. The charging connector contains a wire to each battery junction to allow cell-balanced charging (Photo 5). Battery packs that feature balanced charging usually contain the JST HX connector for charging. The power contacts are another story. They may be JST HSNG style, Dean’s connector or other specialty types.

Photo 5
There seems to be some standardization on balanced Li-ion cell chargers. They require a common plus 1 wire for each cell so each cell can be monitored and charged independently. This means any battery pack with more than one cell requires separate connectors for charging and discharging.

Small Bots ‘n Bats
You’ll find plenty of the small robot bases using AA batteries with a UNO or some other micro platform as its controller. There is nothing wrong with these inexpensive platforms for educational purposes. With a fresh set of batteries, you will usually have predictable behavior. In rather short order however, things will begin to go loony. The motor load will begin to affect the controller as the battery voltage dips. Even at 6 V, with a low drop out regulator, the controller operation and any sensors will quickly become unpredictable. This can be truly a frustrating time for the newbie, as one searches their code for a logic error that might produce the inappropriate action observed, when actually there may be nothing wrong!

You can save a lot of heartache if you just add an extra battery (or two) to raise the voltage to 7.5 V or even better 9 V. I’ve seen kids quickly lose interest or give up entirely simply because they don’t understand what’s happening. I’ve found a better solution is to replace the AAs with a couple of Li-ion 18650 type 3.7 V cells. The 18650 looks like an over-sized AA battery and has battery holders that are similar (Photo 6). You can expect about 2,000 mA-hours from AA cells. The 18650 Li-ion cells pack about three times the energy and they can be popped out and recharged in a few hours. Li-ion flat packs can also be used here, but they are not as “universal” as the 18650 single cells.

Photo 6
Replacing four AA cells with two 18650 Li-ion cells can save a lot of head scratching when unexpected behavior is due to battery droop. The AA cells (4 x 1.5 V) does not leave much headroom when a 5 V regulator is used. Not only is the discharge curve relatively flat for Li-ion cells (2 x 3.7 V) preventing drops in regulation, but the 18650 packs 3 times the energy.

It is a good idea to remove batteries from any equipment that will not be used for extended periods of time. Many devices today—like the ones with auto off functions—have parasitic circuits that continue to draw minuscule currents even when “off”. These will continue to draw down your batteries until they are unusable. Even though Li-ion cells have a protective circuit that prevents them from being discharged below a safe level—approximately 2.75 V/cell—this internal circuitry is parasitic and acts as a tiny load. While self-discharge is only a few percent per month, once the cell voltage drops below a critical voltage this circuitry may not allow it to be recharged. So always store a rechargeable in a “charged” state.

Wireless Charging today
Wireless charging is only in its infancy. Today’s phone chargers are typically less than 5 W. But there is work being done on higher rated equipment. It is proper that these low power devices have such safeguards built-in to prevent unwanted catastrophes. We know from the not too distant past that, along with higher power density materials, comes the potential for calamity unless the proper safeguards are in place. Public education can limit the misuse and/or abuse of lithium technology, just as it has for the safe handling and use of gasoline.

In order for the electric vehicle to become useful, we will need to replenish its range-defining battery charge in fairly short order. This requires extreme infrastructure changes. You can tell by the size of the connectors and cable required for this process that this is high power. The holy grail is for this to happen wirelessly and automatically. From a simple pad embedded in ground where you park your vehicle, to a highway infrastructure that transfers power to your vehicle while you drive. Wireless power transfer is here to stay. Nikola Tesla must be at peace knowing that his work is beginning to bear fruit.

Additional materials from the author are available at:www.circuitcellar.com/article-materials

RESOURCES

Adafruit | www.adafruit.com
RECOM | www.recom-power.com
STMicrolectronics | www.st.com
Texas Instruments | www.ti.com

See the article in the May 334 issue of Circuit Cellar

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Bidirectional Buck-Boost Controller Targets Autonomous Vehicles

Analog Devices has announced the Power by Linear LT8708/-1, a 98% efficient bidirectional buck-boost switching regulator controller that operates between two batteries that have the same voltage. This makes them well-suited for redundancy in self-driving cars. The LT8708/-1 operates from an input voltage that can be above, below or equal to the output voltage, making it well suited for two each 12 V, 24 V or 48 V batteries commonly found in electric and hybrid vehicles. It operates between two batteries and prevents system shutdown should one of the batteries fail. The LT8708/-1 can also be used in 48V/12V and 48V/24V dual battery systems.

The LT8708/-1 operates with a single inductor over a 2.8 V to 80 V input voltage range and can produce an output voltage from 1.3 V to 80 V, delivering up to several kilowatts of power depending on the choice of external components and number of phases. It simplifies bidirectional power conversion in battery/capacitor backup systems that need regulation of VOUT, VIN, and/or IOUT, IIN, both in the forward or reverse direction. This device’s six independent forms of regulation allow it to be used in numerous applications.

The LT8708-1 is used in parallel with the LT8708 to add power and phases. The LT8708-1 always operates as a slave to the master LT8708, can be clocked out-of-phase and has the capability to deliver as much power as the master. One or more slaves can be connected to a single master, proportionally increasing power and current capability of the system.

Another application is for an input voltage to power a load, where this same input voltage is used to power a LT8708/-1 circuit that charges a battery or bank of supercapacitors. When the input voltage goes away, the load maintains power without disruption from the battery or supercaps by way of the LT8708’s bidirectional capability.

Forward and reverse current can be monitored and limited for the input and output sides of the converter. All four current limits (forward input, reverse input, forward output and reverse output) can be set independently using four resistors. In combination with the DIR (direction) pin, the chip can be configured to process power from VIN to VOUT or from VOUT to VIN ideal for automotive, solar, telecom and battery-powered systems.

The LT8708 is available in a 5 mm × 8 mm QFN-40 package. Three temperature grades are available, with operation from –40 to 125°C for the extended and industrial grades and a high temp automotive range of –40°C to 150°C.

Pricing for the LT8708/-1 starts at $6.60 (1,000s).

Analog Devices | www.analog.com

Enter to Win a Wireless Pen-Sized Oscilloscope!

IKALOGIC is giving away an IkaScope! (retail value $379)

The IkaScope WS200 is a pen-shaped battery-powered wireless oscilloscope that streams captured signals to almost any Wi-Fi-connected screen.

GO HERE TO ENTER TO WIN!

The IkaScope WS200 offers a 30 MHz bandwidth with its 200 Msamples/s sampling rate and maximum input of +/-40 Vpp. It provides galvanically-isolated measurements even when a USB connection is charging the internal battery. The IkaScope WS200 will work on desktop computers (Windows, Mac and Linux) as well as on mobile devices like tablets or smartphones. The free application software can be downloaded for whichever platform is needed.
The IkaScope WS200 has no power switch. It detects pressure on the probe tip and turns on automatically. Patented ProbeClick technology saves battery life: all power-consuming circuitry is only turned on when the probe tip is pressed, and the IkaScope WS200 automatically shuts down completely after a short period of non-use. The internal 450 mAh battery lasts about one week with daily regular use before recharging is necessary. An isolated USB connection allows for recharging the internal battery: two LEDs in the unit indicate battery charge and Wi-Fi status.

Clicking the Autoset button on the IkaScope software automatically adjusts gain and time-base to quickly view the signal optimally. The IkaScope WS200 also knows when to measure and when to hold the signal display without the need for a Run/Stop button. The IkaScope’s innovative Automatic History feature saves a capture of the signal when releasing pressure on the ProbeClick tip. The History Database is divided into Current Session and Favorites, where signal captures are permanently saved, even after the application is closed. Previously measured signals can quickly be recalled.

Most desktop oscilloscopes have a static reference grid with a fixed number of divisions, but the IkaScope allows pinch and zoom on touch screens (or zoom in/out with a mouse wheel), stretching the grid and allowing an operator to move and zoom through a signal capture for detailed review. The associated software even has a share button on the screen: simply click on it to share screenshot measurements.

IKALOGIC | www,ikalogic.com

 

Fuel-Gauge ICs Target Mobile and Portable Devices

Maxim Integrated Products has announced the MAX17262 single-cell and MAX17263 single-/multi-cell fuel-gauge ICs. The MAX17262 features just 5.2 µA quiescent current, along with integrated current sensing. The MAX17263 features just 8.2 µA quiescent current and drives 3 to 12 LEDs to indicate battery or system status. Such LEDs are useful in rugged applications that do not feature a display.

According to the company, electronic products powered by small Li-ion batteries struggle to extend device run-times to meet user expectations. Factors such as cycling, aging and temperature can degrade Li-ion battery performance over time. Inaccurate state of charge (SOC) data from an unreliable fuel gauge forces the designer to increase the battery size or compromise the run-time by prematurely shutting the system down, even if there is usable energy available.
Such inaccuracies can contribute to a poor user experience due to abrupt shutdown or an increase in device charging frequency. Designers also strive to get their products to market quickly due to competitive demands. Maxim’s two new fuel-gauge ICs help designers meet end-user performance expectations and time-to-market challenges.

The MAX17262 and MAX17263 combine traditional coulomb counting with the novel ModelGauge m5 EZ algorithm for high battery SOC accuracy without requiring battery characterization. With their low quiescent current, both fuel-gauge ICs prevent current loss during long periods of device standby time, extending battery life in the process.

Both also have a dynamic power feature that enables the highest possible system performance without crashing the battery. In the MAX17262, an integrated Rsense current resistor eliminates the need to use a larger discrete part, simplifying and reducing the board design. In the MAX17263, the integrated, push-button LED controller minimizes battery drain and alleviates the microcontroller from having to manage this function.

The ICs provide accurate time-to-empty (1%) and time-to-full SOC data across a wide range of load conditions and temperatures, using the proven ModelGauge m5 algorithm. The ModelGauge m5 EZ algorithm eliminates the time-consuming battery-characterization and calibration process. A quiescent current of just 5.2 µA for the MAX17262 and 15/8.2 µA for MAX17263 extends run-time, Rsense current resistor (voltage and coulomb counting hybrid) reduces overall footprint and BOM cost, eases board layout

At 1.5 mm × 1.5 mm IC size, the MAX17262 implementation is 30% smaller in size compared to using a discrete sense resistor with an alternate fuel gauge; at 3 mm × 3 mm, MAX17263 is the smallest in its class for lithium-ion-powered devices. The single-/multi-cell MAX17263 also drives LEDs to indicate battery status on a pushbutton press or system status on system microcontroller commands

The MAX17262 is available at Maxim’s website for $0.95 (1000 pieces, FOB USA); the MAX17263 is also on the site for $1.49 (1,000 pieces). Both parts are also available via select authorized distributors. The MAX17262XEVKIT# evaluation kit is available for $60; the MAX17263GEVKIT# is available for $60.

Maxim Integrated | www.maximintegrated.com

Fuel-Gauge ICs Maximize Battery Runtimes for Devices

Maxim Integrated offers the MAX17260 and MAX17261 ModelGauge m5 EZ fuel gauges IC that are well suited for a broad range of Li-ion battery powered applications.  These battery characterization-free solutions provide high levels of accuracy while also offering small size and ease of design.

The MAX17260 and MAX17261, which feature the ModelGauge m5 EZ algorithm, provide a high level of accuracy in fuel gauging compared to competing solutions. This allows designers to maximize their devices’ runtime by preventing premature or sudden device shutdowns, while maintaining a smaller battery size. The fuel gauges, which are housed in an ultra-small 1.5 mm x 1.5 mm package, feature a very low quiescent current of 5.1 µA to minimize draining the battery during long periods of standby time. The products allow designs to be quickly done without battery characterization or calibration.
As devices have become more sophisticated with their feature offerings and increasing power density, designers are now challenged with achieving an enhanced user experience without compromising battery runtimes. There is also a huge market need for highly accurate fuel gauges, as less accuracy may introduce uncertainty that must be compensated with higher battery capacity and larger physical dimensions.

Accurate battery state of charge (SOC) prevents sudden crash and premature device shutdown; Provides easy to understand battery information for end users such as time to empty, time to full under current, as well as hypothetical load conditions; Dynamic power technology enables high system performance without crashing the battery and results in smaller battery size.

The very low quiescent current of 5.1µA of these chips prevent excessive energy loss during long periods of standby time. This battery characterization-free solution offers no battery size limit; MAX17260 offers a high-side Rsense option to simplify ground-plane design; MAX17261 offers a flexible switched resistor divider option to support any number of series cells (multi-cell batteries). The devices support small electronics with 1.5 mm x 1.5 mm wafer-level packaging (WLP) as well as 3 mm x 3 mm TDFN.

The MAX17260 is available for $0.93 (1000-up); MAX17261 is available for $1.22 (1000-up). MAX17260GEVKIT and MAX17261GEVKIT evaluation kits are available for $60.

Maxim Integrated | www.maximintegrated.com

Low-Power MCUs Extend Battery Life for Wearables

Maxim Integrated Products has introduced the ultra-low power MAX32660 and MAX32652 microcontrollers. These MCUs are based on the ARM Cortex-M4 with FPU processor and provide designers the means to develop advanced applications under restrictive power constraints. Maxim’s family of DARWIN MCUs combine its wearable-grade power technology with the biggest embedded memories in their class and advanced embedded security.

Memory, size, power consumption, and processing power are critical features for engineers designing more complex algorithms for smarter IoT applications. According to Maxim, existing solutions today offer two extremes—they either have decent power consumption but limited processing and memory capabilities, or they have higher power consumption with more powerful processors and more memory.
The MAX32660 (shown) offers designers access to enough memory to run some advanced algorithms and manage sensors (256 KB flash and 96 KB SRAM). They also offer excellent power performance (down to 50µW/MHz), small size (1.6 mm x 1.6 mm in WLP package) and a cost-effective price point. Engineers can now build more intelligent sensors and systems that are smaller and lower in cost, while also providing a longer battery life.

As IoT devices become more intelligent, they start requiring more memory and additional embedded processors which can each be very expensive and power hungry. The MAX32652 offers an alternative for designers who can benefit from the low power consumption of an embedded microcontroller with the capabilities of a higher powered applications processor.

With 3 MB flash and 1 MB SRAM integrated on-chip and running up to 120 MHz, the MAX32652 offers a highly-integrated solution for IoT devices that strive to do more processing and provide more intelligence. Integrated high-speed peripherals such as high-speed USB 2.0, secure digital (SD) card controller, a thin-film transistor (TFT) display, and a complete security engine position the MAX32652 as the low-power brain for advanced IoT devices. With the added capability to run from external memories over HyperBus or XcellaBus, the MAX32652 can be designed to do even more tomorrow, providing designers a future-proof memory architecture and anticipating the increasing demands of smart devices.

The MAX32660 and MAX32652 are both available at Maxim’s website and select authorized distributors. MAX32660EVKIT# and MAX32652EVKIT# evaluation kits are also both available at Maxim’s website.

Maxim Integrated | www.maximintegrated.com

Power Management ICs Reduce Charge Times

Texas Instruments (TI) has introduced several new power management chips that enable designers to boost efficiency and shrink power supply and charger solution sizes for personal electronics and handheld industrial equipment. Operating at up to 1 MHz, TI’s new chipset combines the UCC28780 active clamp flyback controller and the UCC24612 synchronous rectifier controller to help cut the size of power supplies in AC/DC adapters and USB Power Delivery chargers in half. For battery-powered electronics that need maximum charging efficiency in a small solution size, TI also offers the bq25910. It is a 6-A three-level buck battery charger enables up to a 60% smaller-solution footprint in smartphones, tablets and electronic point-of-sale devices.

Designed to work with both gallium nitride (GaN) and silicon (Si) FETs, the UCC28780’s advanced and adaptive features enable the active clamp flyback topology to meet modern efficiency standards. With multimode control that changes the operation based on input and output conditions, pairing the UCC28780 with the UCC24612 can achieve and maintain high efficiency at full and light loads.

The chipset delivers efficient operation at up to 1 MHz, enabling a size reduction of 50% and higher power density than solutions today. Multimode control enables efficiency up to 95 percent at full loads and standby power of less than 40 mW, exceeding Code of Conduct (CoC) Tier 2 and U.S. Department of Energy (DoE) Level VI efficiency standards. For designs above 75 W, engineers can also pair the chipset with a new six-pin power-factor correction (PFC) controller, the UCC28056, which is optimized for light-load efficiency and low standby power consumption to achieve compliance with mandatory International Electrotechnical Commission (IEC)-61000-3-2 AC current harmonic limit regulations. Using features such as adaptive zero voltage switching (ZVS) control, engineers can easily design their systems with a combination of resistor settings and controller auto-tuning.

Leveraging an innovative three-level power-conversion technology, the bq25910 enables up to 50 percent faster charging compared to conventional architectures by dramatically reducing thermal loss. With integrated MOFSETs and lossless current sensing, the bq25910 reduces printed circuit board (PCB) space and allows designers to use small 0.33-µH inductors, saving even more space. The bq25910 enables 95 percent charging efficiency, which could take a standard smartphone battery from empty to 70 percent charged in less than 30 minutes. A differential battery-voltage sense line enables fast charging by bypassing parasitic resistance in the PCB for more accurate voltage measurements, even if the battery is placed away from the charger in the system.

Texas Instruments | www.ti.com

 

Power Alternatives for Commercial Drones

330 Power Drones for Web

Solution Options Expand

The amount of power a commercial drone can draw on has a direct impact on how long it can stay flying as well as on what tasks it can perform. But each kind of power source has its tradeoff.

By Jeff Child, Editor-in-Chief

Because extending flight times is a major priority for drone applications, drone system designers are constantly on the lookout for ways to improve the power performance of their products. For smaller, consumer “recreational” style drones, batteries are the obvious power source. But when you get into larger commercial drone designs, there’s a growing set of alternatives. Tethered drone power solutions, solar power technology, fuel cells and advanced battery chemistries are all power alternatives that are on the table for today’s commercial drones.

According to market research firm Drone Industry Insights, the majority of today’s commercial drones use batteries as a power source. As Lithium-polymer (LiPo) and Lithium-ion (Li-ion) batteries have become smaller with lower costs, they’ve been widely adopted for drone use. The advancements in LiPo and Li-ion battery technologies have been driven mainly by the mobile phone industry, according to Drone Industry Insights.

Batteries Still Leading

The market research firm points to infrastructure as the main advantage of batteries. They can be charged anywhere. While Li-Po and Li-Ion are the most common battery technologies for drones, other chemistries are emerging. Lithium Thionyl Chloride batteries (Li-SOCl2) promises a 2x higher energy density per kg compared to LiPo batteries. And Lithium-Air-batteries (Li-air) promise to be almost 7x higher. However, those options aren’t widely available and are expensive. Meanwhile, Lithium-Sulfur-batteries (Li-S) is a possible successor to Li-ion thanks to their higher energy density and the lower costs of using sulfur, according to Drone Industry Insights.

Photo 1 The Graphene Drone FPV Race series LiPo batteries provide lower internal resistance and less voltage sag under load than standard LiPo batteries. As a result, the battery packs stay cooler under extreme conditions

Photo 1
The Graphene Drone FPV Race series LiPo batteries provide lower internal resistance and less voltage sag under load than standard LiPo batteries. As a result, the battery packs stay cooler under extreme conditions

Meanwhile battery vendors continue to roll out new battery products to serve the growing consumer drone market. As an example, in June 2017 battery manufacturer Venom released its new Graphene Drone FPV Race series LiPo batteries. The batteries were engineered for the extreme demands of today’s first person view (FPV) drone racing pilots (Photo 1). The new batteries provide lower internal resistance and less voltage sag under load than standard LiPo batteries. As a result, the battery packs stay cooler under extreme conditions. The Graphene FPV Race series Li-ion batteries are 5C fast charge capable, allowing you to charge up to five times faster. All of the company’s Drone FPV Race packs include its patented UNI 2.0 plug system (Patent no. 8,491,341). The system uses a true Amass XT60 connector that attaches to the included Deans and EC3 adapter.

Chip vendors from the analog IC and microcontroller markets offer resources to help embedded system designers with their drone power systems. Texas Instruments (TI), for example, offers two circuit-based subsystem reference designs that help manufacturers add flight time and extend battery life to quadcopters and other non-military consumer and industrial drones.  …

Read the full article in the January 330 issue of Circuit Cellar

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Note: We’ve made the October 2017 issue of Circuit Cellar available as a free sample issue. In it, you’ll find a rich variety of the kinds of articles and information that exemplify a typical issue of the current magazine.

Massage Vest Uses PIC32

330 Freeman Lead Image

Controlled with an iOS App

These Cornell graduates designed a low-cost massage vest that pairs seamlessly with a custom iOS app. Using the Microchip PIC32 for its brains, the massage vest has sixteen vibration motors that the user can control to create the best massage possible.

By Harry Freeman, Megan Leszczynski and Gargi Ratnaparkhi

As technology continues to make its way into every aspect of our lives, we are increasingly bombarded with more information and given more tools to organize our busy days. For our final project in the Digital Design Using Microcontrollers class at Cornell University, we sought to build technology to help us slow down, enjoy the moment and appreciate our senses. With that in mind, we built a low-cost massage vest that pairs seamlessly with a custom iOS app. The massage vest embeds 16 vibration motors and users can control the vest to create the most comfortable and soothing massage possible. The user first provides their input through the iOS app, which allows for multiple input modes—including custom or preset. The iOS app communicates to a PIC32 microcontroller via a Bluetooth Low Energy (BLE) module and ultimately the PIC32 turns on the vibration motors to complete the user’s requests. A block diagram is shown in Figure 1. Throughout the massage, users can update their settings to adjust to their desires. The complete massage vest costs less than $100—competitive with mass produced massage vests.
330 Freeman Fig 1 for web
Massage vests have historically been used for both pleasure and therapeutic purposes. Several known iOS-controlled massage vests include the iMusic BodyRhythm from iCess Labs and the i-Massager from E-Tek—both presented at the Consumer Electronics Show (CES) in 2013. The former syncs a massage to music for the user’s enjoyment, while the latter provides Transcutaneous Electrical Nerve Stimulation (TENS) as a certified medical device to relieve chronic pain. A group of Cornell students also won an Innovation Award in 2013 from the Cornell University School of Electrical and Computer Engineering for a massage vest called the Sonic Destressing Vest. The Sonic Destressing vest claimed to reduce the serum cortisol levels of its users, potentially reducing the risk of heart disease and depression—among many other chronic issues related to high serum cortisol levels. Those three vests motivated us to build a multi-purpose massage vest that could be extended to provide the particular features of those vests if desired—serving an existing base of users.

This article describes the details of how our massage vest worked so you can build one for yourself. First, we’ll discuss the hardware design that creates the comforting experience the user has with the vest. This will be followed by a discussion of the software that integrates the components together and provides a friendly user interface. Finally, we will conclude with testing and results. …

Read the full article in the January 330 issue of Circuit Cellar

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Note: We’ve made the October 2017 issue of Circuit Cellar available as a free sample issue. In it, you’ll find a rich variety of the kinds of articles and information that exemplify a typical issue of the current magazine.

Integrated Precision Solution for Batteries

Analog Devices has introduced a precision integrated analog front end, controller, and pulse-width modulator (PWM) for battery testing and formation capable of increasing system accuracy and efficiency in lithium-ion battery formation and grading. Compared to conventional technology, the new AD8452 provides 50% more channels in the same amount of space, adding capacity and increasing battery production throughput. The AD8452 uses switching technology that recycles the energy from the battery while discharging and delivers 10 times more accuracy than conventional switching solutions.

AD8452The higher accuracy allows for more uniform cells within battery packs and contributes to longer living batteries in applications such as electric vehicles. It also enhances the safety of manufacturing processes by providing better detection and monitoring to help prevent over and undercharging which can lead to battery failures. The AD8452 delivers bill of material (BoM) cost savings of up to 50% for charging/discharging boards and potential system cost savings of approximately 20%. System simulating demonstration boards will be available and can enable lower R&D engineering cost and shorter time to market for test equipment manufacturers.

AD8452 Features

  • Enables energy recycling battery formation/grading for systems of 20 Ahours or less with up to 95% power efficiency
  • Industry leading precise measurement of current and voltage better than 0.02% over 10⁰C temperature change
  • Solution size 70% smaller than previous product generation

Analog Devices | www.analog.com

January Circuit Cellar: Sneak Preview

The January issue of Circuit Cellar magazine is coming soon. And it’s got a robust selection of embedded electronics articles for you. Here’s a sneak peak.

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Here’s a sneak preview of January 2018 Circuit Cellar:

 

                                     IMPROVING EMBEDDED SYSTEM DESIGNS

Special Feature: Powering Commercial Drones
The amount of power a commercial drone can draw on has a direct effect on how long it can stay flying as well as on what tasks it can perform. Circuit Cellar Chief Editor Jeff Child examines solar cells, fuel cells and other technology options for powering commercial drones.

CC 330 CoverFPGA Design: A Fresh Take
Although FPGAs are well established technology, many embedded systems developers—particularly those used the microcontroller realm—have never used them before. In this article, Faiz Rahman takes a fresh look a FPGAs for those new to designing them into their embedded systems.

Product Focus: COM Express boards
COM Express boards provide a complete computing core that can be upgraded when needed, leaving the application-specific I/O on the baseboard. This brand new Product Focus section updates readers on this technology and provides a product album of representative COM Express products.

TESTING, TESTING, 1, 2, 3

LF Resonator Filter
In Ed Nisley’s November column he described how an Arduino-based tester automatically measures a resonator’s frequency response to produce data defining its electrical parameters. This time he examines the resultsand explains a tester modification to measure the resonator’s response with a variable series capacitance.

Technology Spotlight: 5G Technology and Testing
The technologies that are enabling 5G communications are creating new challenges for embedded system developers. Circuit Cellar Chief Editor Jeff Child explores the latest digital and analog ICs aimed at 5G and at the test equipment designed to work with 5G technology.

                                     MICROCONTROLLERS IN EVERYTHING

MCU-based Platform Stabilizer
Using an Inertial Measurement Unit (IMU), two 180-degree rotation servos and a Microchip PCI MCU, three Cornell students implemented a microcontroller-based platform stabilizer. Learn how they used a pre-programmed sensor fusion algorithm and I2C to get the most out of their design.

Designing a Home Cleaning Robot (Part 2)
Continuing on with this four-part article series about building a home cleaning robot, Nishant Mittal this time discusses the mechanical aspect of the design. The robot is based on Cypress Semiconductor’s PSoC microcontroller.

Massage Vest Uses PIC32 MCU
Microcontrollers are being used for all kinds of things these days. Learn how three Cornell graduates designed a low-cost massage vest that pairs seamlessly with a custom iOS app. Using the Microchip PIC32 for its brains, the massage vest has sixteen vibration motors that the user can control to create the best massage possible.

AND MORE FROM OUR EXPERT COLUMNISTS:

Five Fault Injection Attacks
Colin O’Flynn returns to the topic of fault injection security attacks. To kick off 2018, he summarizes information about five different fault injection attack stories from 2017—attacks you should be thinking about as an embedded designer.

Money Sorting Machines (Part 2)
In part 1, Jeff Bachiochi delved into the interesting world of money sort machines and their evolution. In part 2, he discusses more details about his coin sorting project. He then looks at a typical bill validator implementation used in vending systems.

Overstress Protection
Last month George Novacek reviewed the causes and results of electrical overstress (EOS). Picking up where that left off, in this article he looks at how to prevent EOS/ESD induced damage—starting with choosing properly rated components.

Wearables Drive Low Power Demands

320 Wearablese Lead Image for Web

MCUs & Analog ICs Meet Needs

Wearable devices put extreme demands on the embedded electronics that make them work. Devices spanning across the consumer, fitness and medical markets all need a mix of low-power, low-cost and high-speed processing.

By Jeff Child, Editor-in-Chief

Designers of new wearable, connected devices are struggling to extend battery life for next-generation products, while at the same time increasing functionality and performance in smaller form factors. These devices include a variety of products such as smartwatches, physical activity monitors, heart rate monitors, smart headphones and more. The microcontrollers embedded in these devices must blend extreme low power with high integration. Meanwhile, analog and power solutions for wearables must likewise be highly integrated while serving up low quiescent currents.

Modern wearable electronic devices all share some common requirements. They have an extremely low budget for power consumption,. They tend not to be suited for replaceable batteries and therefore must be rechargeable. They also usually require some kind of wireless connectivity. To meet those needs chip vendors—primarily from the microcontroller and analog markets—keep advancing solutions that consume extremely low levels of power and manage that power. This technology vendors are tasked to keep up with a wearable device market that IDC forecasts will experience a compound annual growth rate (CAGR) of 18.4% in 2020.

MCU and BLE Combo

Following all those trends at once is Cypress Semiconductor’s PSoC 6 BLE. In September the company made its public release of the PSoC 6 BLE Pioneer Kit and PSoC Creator Integrated Design Environment (IDE) software version 4.2 that enable designers to begin developing with the PSoC 6. The PSoC 6 BLE is has built-in Bluetooth Low Energy (BLE) wireless connectivity and integrated hardware-based security.

Photo 1 The PSoC BLE Pioneer Kit features a PSoC 63 MCU with BLE connectivity. The kit enables development of modern touch and gesture-based interfaces that are robust and reliable with a linear slider, touch buttons and proximity sensors based using Cypress’ CapSense capacitive-sensing technology.

Photo 1
The PSoC BLE Pioneer Kit features a PSoC 63 MCU with BLE connectivity. The kit enables development of modern touch and gesture-based interfaces that are robust and reliable with a linear slider, touch buttons and proximity sensors based using Cypress’ CapSense capacitive-sensing technology.

According to Cypress, the company had more than 2,500 embedded engineer customers registering for the PSoC 6 BLE early adopter program in just a few months. Early adopters are using the flexible dual-core architecture of PSoC 6, using the ARM Cortex-M4 core as a host processor and the Cortex-M0+ core to manage peripheral functions such as capacitive sensing, BLE connectivity and sensor aggregation. Early adopter applications include wearables, personal medical devices, wireless speakers and more. Designers are also using the built-in security features in PSoC 6 to help guard against unwanted access to data.  …

Read the full article in the December 329 issue of Circuit Cellar

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Note: We’ve made the October 2017 issue of Circuit Cellar available as a free sample issue. In it, you’ll find a rich variety of the kinds of articles and information that exemplify a typical issue of the current magazine.

Flexible Printed Batteries Target IoT Devices

Semtech and Imprint Energy have announced a collaboration to accelerate the widespread deployment of IoT devices. Imprint Energy will design and produce ultrathin, flexible printed batteries that are especially designed to power IoT devices integrated with Semtech’s LoRa devices and wireless RF technology (LoRa Technology). LoRa Technology, with its long-range, low-power capabilities, is regarded by many as the defacto platform for building low-power wide area networks (LPWAN).

ImprintTo help accelerate a next generation of battery technology, Semtech has invested in Imprint Energy. The companies are working closely to target applications that have the potential to create entirely new markets. The Imprint Energy battery enables new applications which have a thin and small form factor and due to the integrated manufacturing process, the batteries are low cost to produce, making high volume deployments feasible.

A key benefit of the Imprint Energy battery technology is the ability to be printed using multiple types of conventional high-volume printing equipment; this enables quick integration by traditional electronic manufacturers in their existing production lines. Test production runs are currently being processed and the resulting batteries are being used in applications prototypes to validate assumptions and engage early adopters.

Imprint Energy | www.imprintenergy.com

Semtech | www.semtech.com

Buck Converter Extends Battery Life of USB Type-C Gear

Maxim Integrated Products has announced the MAX77756, a 24 V, 500 mA, low quiescent current (IQ) buck converter. The product targets developers of multi-cell, USB Type-C products in need high current, dual inputs and I2C support. USB Type-C products must generate an always-on 3.3 V rail to detect USB insertions. Products utilizing the Power Delivery (PD) voltage range (5 V to 20 V) can generate an always-on (1.8 V /3.3 V /5.0 V) digital supply MAX77756_EVKit_imagerail for the port controller using the MAX77756 step-down converter. In addition, the MAX77756 has a 2 0 μA quiescent current that extends battery life by reducing idle power consumption. To simplify the system design, the MAX77756 has a dual input ideal diode ORing circuit that allows the chip to power from the external USB source if the battery is empty.

Multi-cell battery-operated devices—such as ultrabooks, laptops, tablets, drones and home automation appliances—can easily evolve to Type-C with PD using the flexible MAX77756 power supply. The MAX77756 has a unique combination of wide input voltage range, low quiescent current, higher current load, dual input, and I2C for flexibility and programmability. There is also a default power mode if customers do not want to use the I2C bus. The MAX77756 is a robust IC with short-circuit and thermal protection, 8ms internal soft-start to minimize inrush current, proven current-mode control architecture, and up to 26V input voltage standoff.

Key Advantages

  • Low quiescent current: 1.5 μA Buck and 20 μA MUX for always-on operation
  • High efficiency: Up to 92% with integrated power MUX
  • Small solution size: 2.33mm x 1.42mm 15-bump WLP; no external Schottky array needed
  • Wide input voltage: Operates on full VBUS range (5 V – 20 V) and VBATT (2S, 3S, 4S Li+)

MAX77756 is available from stock and priced at $0.65 (10,000+)..An evaluation board MAX77756EVKIT# (see photo) is available from stock and priced at $70

Maxim Integrated Products | www.maximintegrated.com