Motor Driver Provides Complete Solution for Industrial Designs

Infineon Technologies has launched the IFX007T NovalithIC motor driver for industrial applications. The IFX007T smart half-bridge provides an easy and efficient way to drive brushed and brushless motors, integrating a p-channel high-side MOSFET, an n-channel low-side MOSFET and a driver IC into one package. Along with a microcontroller and power supply, no other devices are necessary to drive a motor.

For many years, Infineon has followed this NovalithIC integrated approach for automotive applications. According to Infineon, the IFX007T now allows industrial system designers to benefit from this experience. It is qualified according to JESD47I and can be used to drive motors with supplies up to 40 V and peak currents up to 55 A. The broad application range includes pumps, healthcare, home and garden appliances as well as industrial automation, fans and many more.

Ease-of-use is a key benefit of the integrated solution. System designers save layout and manufacturing effort while reducing stray inductances and external components. Additionally, only three general purpose microcontroller pins are needed to control a full H-bridge.

The IFX007T has integrated self-protection, including over-temperature and cross-current protection. Within an H-bridge configuration, the half-bridge approach provides logic redundancy—if one device fails, the other can still stop the motor.

Another key benefit is the flexible motor control. The IFX007T can be used in either half-bridge, H-bridge or three-phase configurations. Furthermore, the motor speed can be adjusted via pulse width modulation (PWM) up to 25 kHz. Active freewheeling is possible from either the high side or the low side. An adjustable slew rate enables reduction of electromagnetic emissions.

Infineon Technologies | www.infineon.com

600-V GaN FET Power Stages Support up to 10 kW

Texas Instruments (TI) has announced a new portfolio of ready-to-use, 600-V gallium nitride (GaN), 50-mΩ and 70-mΩ power stages to support applications up to 10 kW. The LMG341x family enables designers to create smaller, more efficient and higher-performing designs compared to silicon field-effect transistors (FETs) in AC/DC power supplies, robotics, renewable energy, grid infrastructure, telecom and personal electronics applications.
TI’s family of GaN FET devices provides a alternative to traditional cascade and stand-alone GaN FETs by integrating unique functional and protection features to simplify design, enable greater system reliability and optimize the performance of high-voltage power supplies.

Dubbed the LMG3410R050, LMG3410R070 and LMG3411R070 TI’s integrated GaN power stage doubles power density and reduces losses by 80 percent compared to silicon metal-oxide semiconductor field-effect transistors (MOSFETs). Each device is capable of fast, 1-MHz switching frequencies and slew rates of up to 100 V/ns. The portfolio is backed by 20 million hours of device reliability testing, including accelerated and in-application hard switch testing. Additionally, each device provides integrated thermal and high-speed, 100-ns overcurrent protection against shoot-through and short-circuit conditions.

Devices for every power level: Each device in the portfolio offers a GaN FET, driver and protection features at 50 mΩ or 70 mΩ to provide a single-chip solution for applications ranging from sub-100 W to 10 kW.

These devices are available now in the TI store in 8-mm-by-8-mm split-pad, quad flat no-lead (QFN) packaging. The LMG3410R050, LMG3410R070 and LMG3411R070 are priced at US$18.69, $16.45 and $16.45, respectively, in 1,000-unit quantities.

Texas Instruments | www.ti.com

950 V Superjunction MOSFETs Boast High Thermal Efficiency

Infineon Technologies has added a new member to its CoolMOS P7 family, the 950 V CoolMOS P7 Superjunction MOSFET. It is designed to meet the needs of applications such as lighting, smart meters, mobile chargers, notebook adapters, AUX power supplies and industrial SMPS applications. This semiconductor solution combines excellent thermal and efficiency performance with lower bill of materials and overall production costs.

The 950 V CoolMOS P7 attributes include outstanding DPAK RDS(on) enabling higher density designs. In addition, the excellent VGS(th) and lowest VGS(th) tolerance make the MOSFET easy to drive and design in. Similar to the other members of the P7 family from Infineon, this component comes with integrated Zener diode ESD protection. This results in better assembly yields and therefore less cost, and fewer ESD-related production issues.

The 950 V CoolMOS P7 enables up to a 1% efficiency increase and from 2˚C to 10˚C lower MOSFET temperature for more efficient designs. This component offers also up to 58% lower switching losses compared to previous generations of the CoolMOS family. Compared to competing technologies in the market the improvement is more than 50%, according to the company.

The 950 V CoolMOS P7 comes in TO-220 FullPAK (shown), TO-251 IPAK LL, TO-252 DPAK, and SOT-223 packaging. This makes it possible to change from THD to SMD device.

Infineon Technologies | www.infineon.com

Motor Drivers Provide Solution for Low- to Mid-Power Applications

STMicroelectronics has released the STSPIN830 and STSPIN840 single-chip drivers that simplify the design of low-to-mid-power motor controls in the 7 V to 45 V range.  The devices contain flexible control logic and low-RDS(ON) power switches for industrial applications, medical technology, and home appliances.
The STSPIN830 for driving 3-phase brushless DC motors has a mode-setting pin that lets users control the three half bridges of the integrated power stage with direct U, V, and W pulse-width modulated (PWM) inputs, or by applying signals to each gate individually for higher control flexibility. A dedicated sense pin for each inverter leg simplifies setting up three-shunt or single-shunt current sensing for Field-Oriented Control (FOC).

The STSPIN840 can drive two brushed DC motors or one larger motor leveraging ST’s well- known, market-proven paralleling concept, which allows the integrated full bridges to be configured as two separate bridges or as a single bridge using the two sets of MOSFETs in parallel for lower RDS(ON) and higher current rating.

Both drivers contain rich features, including PWM current-control circuitry with adjustable off-time, a convenient standby pin for power saving, and protection circuitry including non-dissipative overcurrent protection, short-circuit protection, undervoltage lockout, thermal shutdown, and interlocking to help create robust and reliable drives.

The integrated power stage of each device features ST-proprietary MOSFETs with low RDS(ON) of only 500 mΩ to combine high efficiency with economy. The option to use the output bridges individually or connected in parallel, in the STSPIN840, helps trim the BOM for multi-motor applications.

With their high feature integration and flexibility, the drivers enable more compact and cost-effective controls for industrial, robotic, medical, building-automation, and office-equipment applications. The STSPIN830 is ideal for factory-automation end-points, home appliances, small pumps, and fans for computer or general-purpose cooling. The STSPIN840 targets ATM and money-handling machines, multi-axis stage-lighting mechanisms, thermal printers, textile or sewing machines, and vending machines.

The STSPIN830 and STSPIN840 are both in production now, as 4 mm x 4 mm QFN devices. Pricing for both starts from $1.25 for orders of 1,000 pieces.

Two STM32 Nucleo expansion boards are provided to facilitate product evaluation and build functional prototypes using the STM32 Open Development Environment: X-NUCLEO-IHM16M1 for the STSPIN830 and X-NUCLEO-IHM15A1 for the STSPIN840, both priced at $16.

STMicroelectronics | www.st.com

BLDC Fan Current

Motors and Measurements

Today’s small fans and blowers depend on brushless DC (BLDC) motor technology for their operation. Here, Ed explains how these seemingly simple devices are actually quite complex when you measure them in action.

By Ed Nisley

The 3D printer Cambrian Explosion unleashed both the stepper motors you’ve seen in previous articles and the cooling fans required to compensate for their abuse. As fans became small and cheap, Moore’s Law converted them from simple DC motors into electronic devices, simultaneously invalidating the assumptions people (including myself) have about their proper use.

In this article, I’ll make some measurements on the motor inside a tangential blower and explore how the data relates to the basic physics of moving air.

Brushless DC Motors

Electric motors, regardless of their power source, produce motion by opposing the magnetic field in their rotor against the field in their stator. Small motors generally produce one magnetic field with permanent magnets, which means the other magnetic field must change with time in order to keep the rotor spinning. Motors powered from an AC source, typically the power line for simple motors, have inherently time-varying currents, but motors connected to a DC source require a switching mechanism, called a commutator, to produce the proper current waveforms.

Mechanical commutators date back to the earliest days of motor technology, when motors passed DC power supply current through graphite blocks sliding over copper bars to switch the rotor winding currents without external hardware. For example, the commutator in the lead photo switches the rotor current of a 1065 horsepower marine propulsion motor installed on Fireboat Harvey in 1930, where it’s still in use after nine decades.

Fireboat Harvey’s motors produce the stator field using DC electromagnets powered by steam-driven exciter generators. Small DC motors now use high-flux, rare-earth magnets and no longer need boilers or exhaust stacks.

Although graphite sliding on copper sufficed for the first century of DC motors, many DC motors now use electronic commutation, with semiconductor power switches driven by surprisingly complex logic embedded in a dedicated controller. These motors seem “inside out” compared to older designs, with permanent magnets producing a fixed rotor field and the controller producing a time-varying stator field. The relentless application of Moore’s Law put the controller and power switches on a single PCB hidden inside the motor case, out of sight and out of mind.

Because semiconductor switches eliminated the need for carbon brushes, the motors became known as Brushless DC motors. Externally, they operate from a DC supply and, with only two wires, don’t seem particularly complicated. Internally, their wiring and currents resemble multi-phase AC induction motors using pseudo-sinusoidal stator voltage waveforms. As a result, they have entirely different power supply requirements.

The magnetic field in the rotor of a mechanically commutated motor has a fixed relationship to the stator field. As the rotor turns, its magnetic field remains stationary with respect to the stator as the brushes activate successive sections of the rotor winding to produce essentially constant torque against the stator field. Electronically commutated motors must sense the rotor position to produce stator currents with the proper torque against the moving rotor field. As you’ll see, the motor controller can use the back EMF generated by the spinning rotor to determine its position, thereby eliminating any additional components.

Figure 1
The blower motor current varies linearly with its supply voltage, so the power consumption varies as the square of the voltage. The motor speed depends on the balance between torque and load.

I originally thought Brushless DC (BLDC) motors operated much like steppers, with the controller regulating the winding current, but the switches actually regulate the voltage applied to the windings, with the current determined by the difference between the applied voltage and the back EMF due to the rotor speed. The difference between current drive and voltage drive means steppers and BLDC motors have completely different behaviors.

Constant Voltage Operation

The orange trace along the bottom of Figure 1 shows the current drawn by the 24 V tangential blower shown in Figure 2, without the anemometer on its outlet, for supply voltages between 2.3 V and 26 V. The BLDC motor controller shapes the DC supply voltage into AC waveforms, the winding current varies linearly with the applied voltage and, perhaps surprisingly, the blower looks like a 100 Ω resistor.

Figure 2
An anemometer measures the blower’s outlet air speed and a square of retroreflective tape on the rotor provides a target for the laser tachometer. If you are doing this in a lab, you should build a larger duct with a flow straightener and airtight joints.

The blower’s power dissipation therefore varies as the square of the supply voltage, as shown by the calculated dots in the purple curve. In fact, the quadratic equation fitting the data has 0.00 coefficients for both the linear and constant terms, so it’s as good as simple measurements can get.

As you saw in March (Circuit Cellar #332) and May (Circuit Cellar #334), a stepper motor driven by a microstepping controller has a constant winding current and operates at a constant power. Increasing the supply voltage increases the rate of current change but, because the controller applies the increasing voltage with a lower duty cycle, it doesn’t directly increase power dissipation. …

Read the full article in the July 336 issue of Circuit Cellar

Don’t miss out on upcoming issues of Circuit Cellar. Subscribe today!

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.

Tiny Boost Regulator Eyes Optical Systems

Analog Devices has announced the Power by Linear LTM4661, a low power step-up µModule regulator in a 6.25 mm x 6.25 mm x 2.42 mm BGA package. Only a few capacitors and one resistor are required to complete the design, and the solution occupies less than 1cm² single-sided or 0.5cm² on double- sided PCBs. The LTM4661 incorporates a switching DC/DC controller, MOSFETs, inductors and supporting components. The LTM4661 operates from a 1.8 V to 5.5 V input supply, and continues to operate down to 0.7 V after start-up. The output voltage can be set by a single resistor ranging from 2.5 V to 15 V. The combination of the small, thin package and wide input and output voltage range is ideal for wide range of applications including optical modules, battery-powered equipment, battery-based backup systems, bias voltage for power amps or laser diodes and small DC motors.
The LTM4661 can deliver 4 A continuously under 3.3 VIN to 5 VOUT, and 0.7 A continuously under 3.3 VIN to 12 VOUT. The LTM4661 employs synchronous rectification, which delivers as high as 92% conversion efficiency (3.3 VIN to 5 VOUT). The switching frequency is 1 MHz, and can also be synchronized to an external clock ranging from 500 kHz to 1.5 MHz. The LTM4661 1MHz switching frequency and dual phase single output architecture enable fast transient response to line and load changes and a significant reduction of output ripple voltage. The LTM4661 has three operation modes: Burst Mode operation, forced continuous mode and external sync mode. The quiescent current in Burst Mode operation is only 25 µA, which provides extended battery run time. For applications demanding the lowest possible noise operation, the forced continuous mode or external sync mode minimize possible interference of switching noise.

The LTM4661 features an output disconnect during shutdown and inrush current limit at start-up. Fault protection features include short-circuit, overvoltage and overtemperature protection. It operates from –40℃ to 125℃ operating temperature. Available now, pricing for the LTM4661 starts at $6.98 (1,000s) for  6.25 mm x 6.25 mm x 2.42 mm BGA device.

Analog Devices | www.analog.com

Stepper Motor Back EMF

Supply Voltage vs. Current Control

Continuing with the topic of stepper motors, this time Ed looks at back electromotive force (EMF) and its effects. He examines the relationship between running stepper motors at high speeds and power supply voltage requirements.

By Ed Nisley

Early 3D printers used ATX supplies from desktop PCs for their logic, heater and motor power. This worked well enough—although running high-wattage heaters from the 12 V supply tended to incinerate cheap connectors. More mysteriously, stepper motors tended to run roughly and stall at high printing speeds, even with microstepping controllers connected to the 12 V supply.

In this article, I’ll examine the effect of back EMF on stepper motor current control. I’ll begin with a motor at rest, then show why increasing speeds call for a much higher power supply voltage than you may expect.

Microstepping Current Control

As you saw in my March 2018 article (Circuit Cellar 332), microstepping motor drivers control the winding currents to move the rotor between its full-step positions. Chips similar to the A4988 on the Protoneer CNC Shield in my MPCNC sense each winding’s current through a series resistor, then set the H-bridge MOSFETs to increase, reduce or maintain the current as needed for each step. Photo 1 shows the Z-axis motor current during the first few steps as the motor begins turning, measured with my long-obsolete Tektronix Hall effect current probes, as shown in this article’s lead photo above.

Photo 1 Each pulse in the bottom trace triggers a single Z-axis microstep. The top two traces show the 32 kHz PWM ripple in the A and B winding currents at 200 mA/div. The Z-axis acceleration limit reduces the starting speed to 18 mm/s = 1,100 mm/min.

The upper trace (I’ll call it the “A” winding) comes from the black A6302 probe clamped around the blue wire, with the vertical scale at 200 mA/div. The current starts at 0 mA and increases after each Z-axis step pulse in the bottom trace. Unlike the situation in most scope images, the “ripple” on the trace isn’t noise. It’s a steady series of PWM pulses regulating the winding current.

The middle trace (the “B” winding) increases from -425 mA because it operates in quadrature with the A winding. The hulking pistol-shaped Tektronix A6303 current probe, rated for 100 A, isn’t well-suited to measure such tiny currents, as you can see from the tiny green stepper motor wire lying in the gaping opening through the probe’s ferrite core. Using it with the A6302 probe shows the correct relation between the currents in both windings, even if its absolute calibration isn’t quite right.

Photo 2 zooms in on the A winding current, with the vertical scale at 50 mA/div, to show the first PWM pulse in better detail. The current begins rising from 0 mA, at the rising edge of the step pulse, as the A4988 controller applies +24 V to the motor winding and reaches 110 mA after 18 µs. The controller then applies -24 V to the winding by swapping the H bridge connections. This causes the current to fall to 40 mA, whereupon it turns on both lower MOSFETs in the bridge to let the current circulate through the transistors with very little loss.

Photo 2
Zooming in on the first microstep pulse of Photo 1 shows the A4988 driver raising the stepper winding current from 0 mA as the motor starts turning. The applied voltage and motor inductance determine the slope of the current changes.

The next PWM cycle starts 15 µs later, in the rightmost division of the screen, where it rises from the 40 mA winding current set by the first pulse. It will also end at 110 mA, although that part of the cycle occurs far off-screen. You can read the details of the A4988 control algorithms and current levels in its datasheet, with the two-stage decreasing waveform known as “mixed decay” mode.

Although the H-bridge MOSFETs in the A4988 connect the motor windings directly between the supply voltage and circuit ground, the winding inductance prevents the current from changing instantaneously. The datasheet gives a nominal inductance of 4.8 mH, matching what I measured, but you can also estimate the value from the slope of the current changes.. . …

Read the full article in the May 334 issue of Circuit Cellar

Don’t miss out on upcoming issues of Circuit Cellar. Subscribe today!
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.

Compact Power Regulator Targets FPGAs, GPUs and ASICs

Analog Devices has announced the Power by Linear LTM4646, a dual 10 A or single 20 A output, step-down µModule point-of-load regulator from 5V or 12V input supply rails. The LTM4646 includes the inductors, MOSFETs, a DC/DC controller and supporting components and is housed in a 11.25 mm x 15 mm x 5.01 mm BGA package. Compared to the prior 2 x single 10 A output module solutions, the LTM4646 reduces the solution size of more than 25%.
With its dual regulator design, small package size, and precise voltage regulation, the LTM4646 meets the PCB area constraints of densely populated system boards to power low voltage and high current devices such as FPGAs, ASICs, microprocessors and GPUs. Applications include PCIe boards, communication infrastructure, cloud computing-based systems, as well as medical, industrial, and test and measurement equipment.

Total output voltage DC accuracy is guaranteed at ±1.5% over line, load and temperature (–40°C to 125°C). Moreover, the onboard remote sense amplifiers on both outputs compensate for voltage drop caused by trace impedance of the PC board due to large load currents. The LTM4646 has selectable internal or external feedback loop compensation, enabling users to optimize loop stability and transient performance while minimizing the number of output capacitors. The peak efficiency at 12 VIN to 1.0 VOUT is 86%. With 200LFM air flow, the LTM4646 delivers a full 20A  continuously up to 85°C ambient. The current mode architecture allows multiphase parallel operation to increase output current with very good current sharing.

Standalone, the LTM4646 operates from 4.5 V to 20 V input range. When 5 V external bias is available, the device can operate from 2.375 V. The output voltages are adjustable from 0.6 V to 5.5 V, enabling the device to generate not only low voltage for digital devices but also 2.5 V, 3.3 V and  5V, which are commonly needed in system bus voltages. The switching frequency can be programmed from 250 kHz to 1.3 MHz with one resistor, and can also be synchronized to an external clock ranging from 300 kHz to 1 MHz for noise-sensitive applications. Additionally, it features overvoltage and overcurrent protection. The LTM4646 operates from –40°C to 125°C.

Summary of Features: LTM4646

  •     Dual 10A or Single 20A Output
  •     Wide Input Voltage Range: 4.5V to 20V
  •     2.375VMIN with CPWR Bias
  •     Output Voltage Range: 0.6V to 5.5V
  •     ±1.5% Maximum Total DC Output Error
  •     Multiphase Current Sharing
  •     Differential Remote Sense Amplifier, Each Channel
  •     Internal or External Compensation
  •     11.25mm x 15mm x 5.01mm BGA Package
  •     BGA Ball Finishes Available: SAC305 (RoHS), SnPb (63/37)

 

Linear Technology | www.linear.com