Perfecting Power
Boosting battery life and efficiency is a major goal for many embedded systems. Analog IC vendors are smoothing the way with innovative chips for monitoring, controlling and charging batteries.
Managing battery power is a critical function for all sorts of battery-powered systems, including power tools, wearable electronics, IoT edge devices and electric vehicles. Innovations in power management ICs, fuel-gauge ICs, battery monitoring ICs and more are helping to provide improved power efficiency for diverse applications.
There are many facets to managing batteries in embedded systems. To meet the ever-present goal of extending battery lifetimes and battery efficiencies requires solutions for monitoring and charging batteries, as well as efficient power conversion devices. Over the past 12 months, analog ICs vendors have rolled out several innovative solutions both for portable, battery-powered systems and for the particular needs for electric vehicle battery management.
FUEL GAUGE ICS
Along those lines, in August Maxim Integrated announced fuel gauge ICs that company claims offer the most configurable settings for battery safety in the industry and uniquely allow fine tuning of voltage and current thresholds based on various temperature zones. The newest 1-cell, pack-side ICs in this portfolio are the MAX17301 and the MAX17311 (Figure 1). These ICs also offer a secondary protection scheme in case the primary protection fails. This secondary protection scheme permanently disables the battery by overriding a secondary protector or blowing a fuse in severe fault conditions.
All ICs in the family are equipped with Maxim’s patented ModelGauge m5 EZ algorithm that delivers highest state-of-charge (SOC) accuracy that on average offers 40% better accuracy than competitive offerings and eliminates the need for battery characterization. These fuel gauges also offer the industry’s lowest quiescent current (IQ)—up to 80% lower than the nearest competitor according to Maxim, and feature SHA-256 authentication to safeguard the systems from counterfeit batteries.
Conventional battery protectors monitor voltage and current, and in some cases include temperature monitoring, says Maxim. These options make the system vulnerable to unexpected crashes because battery SOC isn’t factored in when triggering an undervoltage cut-off decision. The market lacks a solution that allows deeper configuration of voltage or current thresholds based on multiple temperature environments.
Maxim’s devices provide advanced battery protection to ensure safe charging and discharging in a wide range of applications with 2-level Li-ion protector control for abnormal voltage, current and temperature conditions. The ICs protect against counterfeiting and cloning with SHA-256 authentication and provide unique as well as dynamic keys for every battery.
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To enable high accuracy, the chips offer cycle+ age forecasting that provides easy-to-understand prediction of remaining battery life for battery replacement planning or to control fast-charging. Battery life logging stores the history of operating conditions experienced by the pack over its lifetime. Support for long product shelf-life and runtime is served by an operating IQ of 24µA active/18µA low power with protector FETs “on” and 7µA with protector FETs “off.”
BATTERY CHARGER IC
With its focus on the charging side of battery management, in September Texas Instruments (TI) introduced a switching battery charger IC that supports a termination current of 20mA. Compared to competing devices, which typically support a termination current higher than 60mA, TI’s BQ25619 enables 7% higher battery capacity and longer runtime, says TI. The BQ25619 charger also delivers three-in-one boost converter integration and ultra-fast charging, offering 95% efficiency at a 4.6V and 0.5A output (Figure 2). Additionally, with the industry’s lowest quiescent current, the new charger can double the shelf life of ready-to-use electronics.
The BQ25619 charger is designed to help engineers design more efficiently for small medical and personal electronics applications such as hearing aids, earbuds and wireless charging cases, IP network cameras, patient monitoring devices and personal care applications.
An ultra-low termination current of 20mA increases battery capacity and runtime by up to 7%. The BQ25619’s settable top-off timer further increases run time, enabling users to charge their devices less frequently. The BQ25619 reduces battery leakage down to 6µA in ship mode, which conserves battery energy to double the shelf life for the device. While in battery-only operation, the device consumes only 10µA, to support standby systems.
The BQ25619 includes integrated charge, boost converter and voltage protection to support efficient design for space-constrained applications and eliminate the external inductor required by previous-generation charger ICs. Due to its integrated bidirectional buck or boost topology, the BQ25619’s charging and discharging capabilities require just a single power device. The device is offered in a 24-pin wafer quad flatpack no-lead (WQFN) package. The 30-pin BQ25618, with similar features, is offered in a smaller wafer chip-scale package (WCSP).
WIRELESS CHARGING IC
Many wearable devices aren’t suited to be powered by replaceable batteries. As a result, they typically need to be recharged. Wireless (cordless) battery charging is beginning to take hold as a solution. Feeding such needs, Analog Devices offers its LTC4126 as an expansion of its offerings in wireless battery charging. The LTC4126 combines a wireless powered battery charger for Li-Ion cells with a high efficiency multi-mode charge pump DC-DC converter, providing a regulated 1.2V output at up to 60 mA (Figure 3).
Charging with the LTC4126 allows for a completely sealed end product without wires or connectors and eliminates the need to constantly replace non-rechargeable (primary) batteries. The efficient 1.2V charge pump output features pushbutton on/off control and can directly power the end product’s ASIC. This greatly simplifies the system solution and reduces the number of necessary external components. The device is ideal for space-constrained low power Li-Ion cell powered wearables such as hearing aids, medical smart patches, wireless headsets and IoT devices.
The LTC4126, with its input power management circuitry, rectifies AC power from a wireless power receiver coil and generates a 2.7V to 5.5V input rail to power a full-featured constant-current/constant-voltage battery charger. Features of the battery charger include a pin selectable charge voltage of 4.2V or 4.35V, 7.5mA charge current, automatic recharge, battery temperature monitoring via an NTC pin, and an onboard 6-hour safety charge termination timer.
Low-battery protection disconnects the battery from all loads when the battery voltage is below 3.0V. The LTC4126’s charge pump switching frequency is set to 50kHz/75kHz to keep switching noise out of the audible range, ideal for audio related applications such as hearing aids and wireless headsets. The IC is housed in a compact, low profile (0.74 mm) 12-lead 2mm × 2mm LQFN package. The device is guaranteed for operation from –20°C to 85°C in E-grade.
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SOLUTION FOR 14 Li-Ion CELLS
Electric and hybrid vehicles have very special requirements when it comes to managing their battery subsystems. Feeding those needs, Renesas Electronics in August announced its fourth-generation Li-Ion battery management IC that offers high lifetime accuracy. The ISL78714 provides accurate cell voltage and temperature monitoring, along with cell balancing and extensive system diagnostics to protect 14-cell Li-Ion battery packs while maximizing driving time and range for hybrid and electric vehicles (Figure 4).
The ISL78714 monitors and balances up to 14 series-connected cells with ±2mV accuracy across automotive temperature ranges, letting system designers make informed decisions based on absolute voltage levels. The ISL78714 includes a precision 14-bit analog-to-digital converter and associated data acquisition circuitry. The device also offers up to six external temperature inputs (two available from GPIOs) and includes fault detection and diagnostics for all key internal functions.
The ISL78714 meets the stringent reliability and performance requirements of battery pack systems for all electric vehicle variants, with safety features, enabling automotive manufacturers to achieve the ISO 26262 automotive safety integrity level (ASIL D). In addition, the ISL78714 monitors and reads back over/under voltage, temperature, open wire conditions, and fault status for 112 cells in less than 10ms, or 70 cells in 6.5ms.
Multiple ISL78714s can be connected together via a proprietary daisy chain that supports systems up to 420 cells (30 ICs) that provide industry-leading transient and EMC/EMI immunity, exceeding automotive requirements. The ISL78714’s daisy-chain architecture uses low-cost capacitive or transformer isolation, or a combination of both, with twisted pair wiring to stack multiple battery packs together while protecting against hot plug and high voltage transients. A watchdog timer automatically shuts down a daisy-chained IC if communication is lost with the master MCU. Mass production quantities of the ISL78714 Li-ion battery management IC are available now in a 64-lead TQFP package.
ELECTRIC VEHICLE DESIGN WIN
In December, Analog Devices (ADI) announced that Rimac Automobili is planning to incorporate ADI’s precision battery management system (BMS) ICs into Rimac’s BMS. ADI’s technology provides Rimac’s BMS with the ability to extract maximum energy and capacity out of its batteries by calculating reliable SOC and other battery parameters at any given time, according to ADI.
The Rimac C_Two is a fully electric hypercar capable of speeds of up to 258 miles per hour. With 1,914 horsepower under the hood, the C_Two accelerates 0 to 60 mph in 1.85 seconds and 0 to 186 mph in 11.8 seconds. To support these high-performance outputs, the Rimac team designs and engineers superior underlying technologies, such as electric drivetrain and battery packs.
BMS technology acts as the “brains” behind battery packs by managing the output, charging and discharging as well as providing precision measurements during vehicle operation. A BMS also provides vital safeguards to protect the battery from damage. A battery pack consists of groups of individual battery cells that work seamlessly together to deliver maximum power output to the car. If the cells go out of balance, the cells can get stressed leading to premature charge termination and a reduction in the battery’s overall lifetime. ADI’s battery management ICs deliver the highly accurate measurements, resulting in safer vehicle operation and maximizing vehicle range per charge.
ASIL-D COMPLIANT IC
Safety standards compliance is a key concern in electric vehicles. Automotive designers can now achieve ASIL-D compliance for automotive applications using just a single chip for a safer, more cost-effective battery management system with the MAX17853 battery monitor IC from Maxim Integrated (Figure 5). Targeting mid-to-large cell count configurations for automotive applications, such as battery packs for electric and hybrid vehicles, MAX17853’s flexible architecture called Flexpack enables engineers to rapidly make changes to their module configurations to quickly respond to market demands.
Achieving safety compliance in automotive applications can require adding redundant components to the system. Maxim claims that the MAX17853 is the only ASIL-D-compliant IC for mid-to-large cell count configurations, enabling engineers to create a system that meets the highest level of safety for voltage, temperature and communication. Also contributing to higher safety is the device’s advanced battery cell balancing system, which automatically balances each cell by time and voltage to minimize risk of overcharging.
System developers can achieve all this without adding extra components such as redundant comparators to help achieve smaller form factors, says Maxim. In addition, the MAX17853 reduces system bills of materials (BOM) cost by up to 35% compared to competitive solutions to allow the customer to achieve lower overall cost for their BMS solution.
Flexibility is also important because engineers typically must design and qualify separate boards and BOMs for each different module configuration. The MAX17853 is the industry’s only IC supporting multiple channel configurations (8 to 14 cells) with one board. This enables engineers to reduce design time by up to 50% through reduced validation and qualification time. For example, they can cut their development time and qualification efforts in half by using the same board for 8s and 14s modules. 
RESOURCES
Analog Devices | www.analog.com
Maxim Integrated | www.maximintegrated.com
Renesas Electronics | www.renesas.com
Texas Instruments | www.ti.com
PUBLISHED IN CIRCUIT CELLAR MAGAZINE • JANUARY 2020 #354 – Get a PDF of the issue
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Jeff served as Editor-in-Chief for both LinuxGizmos.com and its sister publication, Circuit Cellar magazine 6/2017—3/2022. In nearly three decades of covering the embedded electronics and computing industry, Jeff has also held senior editorial positions at EE Times, Computer Design, Electronic Design, Embedded Systems Development, and COTS Journal. His knowledge spans a broad range of electronics and computing topics, including CPUs, MCUs, memory, storage, graphics, power supplies, software development, and real-time OSes.
