Battery management considerations for portable medical applications - PowerPoint PPT Presentation

Battery management considerations for portable medical applications Düsseldorf, November 16-17, 2017 Ivo Marocco – BMS WW Solutions and Marketing director i-marocco@ti.com www.ti.com/battery 1

Agenda Fundamentals of battery management building blocks – Charger, Gauge, Protection Battery design considerations for – Wearable products – Back-up systems BMS product recommendation 2

Charger A Basic Battery Charger I or V Charger Voltage Charger Current Time • Battery charger: - Constant voltage and constant current loops - High accuracy of voltage regulation - Battery can be a load or a source

Key Charger Parameters to Consider Charger Inputs: System: • Min Voltage • Min Voltage Type • Current • Current • Linear (<1.5A) Adaptor • Switch Mode (>1.5A) and/or Battery REGN USB • Chemistry • Configuration (?S?P) System on when • Capacity charging? Control Interface • Power path • Standalone • I2C Safety and Protection Host • SMBus • OVP (Input, BAT and OTG) • OCP /UCP… • Thermal Regulation Packaging: CSP or QFN

Charger Which charger do I need for my application? Linear Switch-mode • Low charge current < 1.0 or 1.5A • Higher charge current > 1.5A • Good thermal performance across wider • Thermal performance depends on V OUT - V IN and V OUT – V IN range PCB layout / copper area • Proper layout needed for best EMI • No EMI concern performance • Simple • High efficiency • Higher cost • Lower cost + V IN Q2 System V IN Battery Q3 Battery Linear Charger Switch Charger

Gauge Gauging concept

Gauge Hardware features (minimum) • Optimized hardware for – Low power consumption (battery powered and all that…) – ADC for • voltage measurements (1mV accuracy target) • temperature measurements – Coulomb counter (integrating ADC) • accumulating passed charge • current measurements – CPU/RAM bq27621 SDA BAT Voltage PACK+ ADC SCL – Non-volatile Memory with Mux CPU GPOUT VDD Die 1.8V 0.47uF • Flash or EEPROM and/or ROM BIN Temp LDO Sensor PACK- VSS

Gauge Gas gauge placement Host System Battery Pack PACK+ Vcc REGIN LDO REG25 BAT Host CPU SE Pack-side or Power HDQ TS Management Gas Gauge Controller (bq27541) SRP Protection SRN IC Vss PACK- Host System Battery Pack VCC REGIN CE LDO PACK+ Battery Voltage Protection Low Sense IC Host CPU System-side or Gas Temp Power Sense I 2 C DATA Gauge T Management Controller (bq27520) CHG FETs BAT_GD PACK- DSG Current SOC_INT Sense

Protection The goal is to avoid catastrophic failure Possible Battery System Malfunctions – Short Circuits: • cell internal • pack internal • pack external – Over-charge – Over-discharge – Over-heating 9

Protection Possible Battery System Malfunctions • Short Circuits – cell internal pack internal ✓ – pack external ✓ – Over-charge ✓ • Over-discharge ✓ • Over-heating ✓ • This solution is called a Primary Protector 10

Protection Possible Battery System Malfunctions What happens if the FETs are shorted, or the gate drivers are stuck such that the FETs are not turned off? 11

Protection A Second Protector Makes an Appearance This solution is called a Secondary Protector Measuring over- voltage only, the protector’s output blows a chemical fuse, physically de- energizing the pack The threshold voltage of a secondary protector is always higher than the thresholds of the primary protector. 12

Considerations for small battery design capacity EEQ • Longer run-time btw recharge cycles ❖ Ultra-low quiescent current, ultra low-power components ❖ Accurate charge termination voltage • Fast charging needed? (rate>1C) ❖ Flexibility thru I2C • Accurate battery gauging ❖ Extended battery run-time

Why accurate charge termination for small cell ? V BATT (Volts) I BATT (mA) 5.0 40 4.0 30 3.0 20 2.0 Extra capacity achieved – 2mAh 10 1.0 0 0 30 60 90 120 Charge Time (minutes) Charge Time - min • Charged 41mAh battery at 40mA fast charge current (1C) • Termination at 4mA (10%) or 1mA • Shaded area represents additional 5% capacity restored on each charge

Fast Charging using the bq25120A Unregulated PG PMID Load IN VINLS BQ25120 GND SYS MCU / SW CD SYSTEM HOST SDA SCL LS / LDO INT <100mA Load RESET LSCTRL BAT MR IPRETERM ISET + TS ILIM NTC - IN • I2C allows the support of multiple battery chemistries for single-cell applications ✓ Can adjust battery regulation voltage 3.6V – 4.65V • Use the VBAT to monitor the battery voltage during charge ✓ Dynamically change fast charge current 15

No I2C available? – bq25100 is the solution < 75 nA 16

Why battery gauging accuracy is important • Small capacity cells are more sensitive to small changes in load current and temperature • Small changes can impact critical decisions made by the system – Having accurate information about the state of the battery is paramount • More accurate gauging extends battery life and prevent premature shutdowns • Cell impedance scales inversely proportional to capacity – the smaller the capacity the larger the cell impedance • Higher cell resistance means – more capacity sensitivity to cell aging (cycling) – more capacity sensitivity to temperature fluctuations – more voltage sensitivity to small changes in current • Currents are small and this requires high precision measurements to detect changes • Three key parameters for determining the chemical state of the battery are Current, Voltage and Temperature 17

Why battery gauging accuracy is important • Cell resistance increases closer to End of Discharge • Low temp increases cell resistance • Small current pulses < 30mA cause large dips in cell 50 ̊C voltage • Higher the resistance the 25 ̊C 0 ̊C longer cell takes to relax between pulses • Large dips in voltage can trigger false system reactions without accurate gauging 18

Measurement Accuracy • Voltage – Accurate voltage measurements are critical for • Initialization of relaxed cell • Updates during self-discharge of cell • Correction for coulomb counting error – TI fuel gauges use a 15 bit ADC to provide accurate voltage measurements • Current – Accurate coulomb counting is critical to capture • low sleep currents • short load spikes • proper passed charge – TI fuel gauges have a dedicated 15 bit integrating ADC (i.e. coulomb counting hardware) • Temperature – Accurate temperature measurements are critical for proper consideration of • resistance • predicted runtime – TI fuel gauges provide flexible temperature measurement options • External measurements with cell’s thermistor or board hotspot • Host can write the temperature to the fuel gauge • Internal IC temperature measurements 19

bq27426: System Side IT Single Cell Fuel Gauge Features Benefits • Single Cell Li-ion Fuel Gauge with integrated LDO • Selectable chemistry profiles − Make it easy to use with minimum configuration − Power directly from battery − Solve customer inventory management across − Supports embedded battery multiple projects • Ultra low power consumption in Normal and Sleep modes • Lower power sleep consumption leading to longer battery • Impedance Track TM Technology run time − Multiple selectable pre-programmed profiles for • Quick time to market with no additional 4.2V, 4.35V & 4.4V cells algorithm/firmware development needed − Remaining Capacity and State of Charge • Configurable interrupts save system power and frees up − host from continuous polling Auto-compensation for aging, temperature, rate • External sense resistor supports high currents of charge/discharge • External thermistor supports accurate temp. sensing − State of Health (SOH) reporting Typical Application Schematic • 400 KHz I2C enables faster configuration • Configurable Alert Interrupt to Host • Smallest system side fuel gauge • External sense resistor Applications • Internal temperature sensor/External thermistor • Smartphones, Tablets • 400KHz I2C Communication • Wearable • 9 pin CSP (1.6mm x 1.6mm x 0.5mm) • Building automation • Portable Medical/Industrial Handsets • Portable audio • Gaming