Battery management considerations for portable medical applications - - PowerPoint PPT Presentation

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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

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Agenda

Fundamentals of battery management building blocks

– Charger, Gauge, Protection

Battery design considerations for

– Wearable products – Back-up systems

BMS product recommendation

A Basic Battery Charger

Time

Charger Voltage Charger Current

I or V

• Battery charger:
• Constant voltage and constant current loops
• High accuracy of voltage regulation
• Battery can be a load or a source

Charger

REGN

System:

• Min Voltage
• Current

Adaptor and/or USB

Inputs:

• Min Voltage
• Current

Battery

• Chemistry
• Configuration (?S?P)
• Capacity

Control Interface Packaging: CSP or QFN

System on when charging?

• Power path

Type

• Linear (<1.5A)
• Switch Mode (>1.5A)

Key Charger Parameters to Consider

Safety and Protection

• OVP (Input, BAT and OTG)
• OCP/UCP…
• Thermal Regulation

Host

• Standalone
• I2C
• SMBus

Charger

Which charger do I need for my application?

Linear

• Low charge current < 1.0 or 1.5A
• Thermal performance depends on VOUT - VIN and

PCB layout / copper area

• No EMI concern
• Simple
• Lower cost

Switch-mode

• Higher charge current > 1.5A
• Good thermal performance across wider

VOUT – VIN range

• Proper layout needed for best EMI

performance

• High efficiency
• Higher cost

+

Linear Charger Battery VIN

Q3 Q2

Battery VIN System Switch Charger

Charger

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 – Non-volatile Memory

• Flash or EEPROM and/or ROM

0.47uF

SDA VDD CPU 1.8V LDO Die Temp Sensor SCL GPOUT BAT Voltage ADC with Mux VSS

bq27621

BIN PACK+ PACK-

Gauge

Gas gauge placement

Host System

Battery Pack

PACK- Protection IC

CHG DSG Temp Sense BAT_GD Current Sense

I2C T PACK+

Voltage Sense Battery Low

FETs

Gas Gauge

(bq27520)

Host CPU

• r

Power Management Controller

LDO REGIN VCC DATA SOC_INT CE

System-side

Battery Pack

PACK- Protection IC PACK+ TS

Gas Gauge

(bq27541)

LDO

REG25 REGIN Vcc SRP SRN SE BAT Vss

HDQ

Host CPU

• r

Power Management Controller

Host System

Pack-side

Gauge

The goal is to avoid catastrophic failure

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Possible Battery System Malfunctions

– Short Circuits:

• cell internal
• pack internal
• pack external

– Over-charge – Over-discharge – Over-heating

Protection

Possible Battery System Malfunctions

• Short Circuits

– cell internal – pack internal ✓ – pack external ✓

• Over-charge ✓
• Over-discharge ✓
• Over-heating ✓

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This solution is called a Primary Protector

Protection

Possible Battery System Malfunctions

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What happens if the FETs are shorted, or the gate drivers are stuck such that the FETs are not turned

• ff?

Protection

A Second Protector Makes an Appearance

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Measuring over- voltage only, the protector’s

• utput blows a

chemical fuse, physically de- energizing the pack This solution is called a Secondary Protector The threshold voltage of a secondary protector is always higher than the thresholds of the primary protector.

Protection

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 ?

Charge Time - min

5.0 4.0 3.0 2.0 1.0 40 30 20 10

• 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

VBATT (Volts) IBATT (mA) 30 60 90 120 Charge Time (minutes)

Extra capacity achieved – 2mAh

Fast Charging using the bq25120A

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• 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

GND

HOST

SDA SCL INT SW BAT MR

BQ25120 MCU / SYSTEM

• +

NTC

TS LS / LDO

<100mA Load

IN SYS RESET LSCTRL VINLS

Unregulated Load

PMID PG IPRETERM ISET ILIM CD IN

No I2C available? – bq25100 is the solution

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< 75 nA

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

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Why battery gauging accuracy is important

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• Cell resistance increases

closer to End of Discharge

• Low temp increases cell

resistance

• Small current pulses < 30mA

cause large dips in cell voltage

• Higher the resistance the

longer cell takes to relax between pulses

• Large dips in voltage can

trigger false system reactions without accurate gauging

25 ̊C 0 ̊C 50 ̊C

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

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bq27426: System Side IT Single Cell Fuel Gauge

• Single Cell Li-ion Fuel Gauge with integrated LDO

− Power directly from battery − Supports embedded battery

• Ultra low power consumption in Normal and Sleep modes
• Impedance TrackTM Technology

− Multiple selectable pre-programmed profiles for 4.2V, 4.35V & 4.4V cells − Remaining Capacity and State of Charge − Auto-compensation for aging, temperature, rate

• f charge/discharge

− State of Health (SOH) reporting

• Configurable Alert Interrupt to Host
• External sense resistor
• Internal temperature sensor/External thermistor
• 400KHz I2C Communication
• 9 pin CSP (1.6mm x 1.6mm x 0.5mm)

Selectable chemistry profiles

• Make it easy to use with minimum configuration

− Solve customer inventory management across − multiple projects Lower power sleep consumption leading to longer battery

• run time

Quick time to market with

• no additional

algorithm/firmware development needed Configurable

• interrupts save system power and frees up

host from continuous polling External sense resistor supports high currents

• External thermistor supports accurate temp. sensing
• 400
• KHz I2C enables faster configuration

Smallest system side fuel gauge

• Applications

Smartphones, Tablets

• Wearable
• Building automation
• Portable Medical/Industrial Handsets
• Portable audio
• Gaming
• Features

Benefits Typical Application Schematic

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• Patented Dynamic Voltage Correlation (DVC)™

battery fuel gauging technology

• Turn Key Solution with complete CPU and battery

fuel gauge firmware

• System/Pack side implementation
• I2C communications interface
• No sense resistor required (no coulomb counter

required)

• Internal temperature sensor
• ROM based configuration
• WCSP package

Enables lower terminate voltage of system and

• extends run time from battery

No external battery algorithm and firmware

• development needed

Provides flexibility in pack

• selection

Three

• chemIDs for 1 orderable part number.

Works with any current (high or low)

• No
• pre-programming of gauge necessary in

production Small solution

• size

Can achieve very low power gauging

• Applications

Portable Medical and Industrial

• Fitness Monitors, smart watches
• Smart phones, feature phones and
• tablets

DSC, portable audio and PMP

• Features

Benefits

0.47uF

SDA VDD CPU 1.8V LDO Die Temp Sensor SCL GPOUT BAT Voltage ADC with Mux VSS

bq27621/22

BIN PACK+ PACK-

bq27621-G1

Dynamic Voltage Correlation System-Side Fuel Gauge – No sense resistor!

End-of-Service Determination for battery back-up systems

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Batteries used in rarely discharged applications such as backup

• systems may sit fully charged for months or years without any load

current, until they are suddenly needed A challenge in such systems is knowing when the battery

• has degraded such that it can no longer support the

required backup application This is conventionally supported using a maintenance

• cycle, which typically requires taking the backup offline

The End

• of-Service (EOS) Determination algorithm in

bq34110 enables evaluation of the battery status using only 1-2% discharge “Learning Pulses” Guaranteed Backup Learning Cycle Min Operating Voltage V t Upto 93% Discharge

End-of-Service Determination

Normal Operation System under power with battery charged and maintained – Normal CEDV algorithm is used with slight change in configuration settings – Normal Charging with charging voltage optimized for longevity, e.g., – 4.1V This

• FullChargeCapacity() is used for reporting

Learning Pulses

Controlled, limited discharge avoids impact to guaranteed capacity available – Timing between Learning Pulses is important for algorithm –

Through multiple Learning Pulses enough data is gathered to determine approaching end-of-service

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End-of-Service Determination

Charge-before-Discharge Learning Pulse

– ChargingVoltage() is increased slightly, to charge battery higher than typical – After relaxation, a learning discharge pulse is triggered, discharging ~1-2% of capacity

• ver a fixed time period

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Guaranteed Backup Min Operating Voltage t V relaxation charge Learning discharge (~1-2%) relaxation

End-of-Service Determination

Discharge-before-Charge Learning Pulse

Battery is charged to existing – ChargingVoltage() level and allowed to relax A learning discharge pulse is triggered, discharging ~ – 1-2% of capacity over a fixed time period After pulse completes, battery can be recharged back to – ChargingVoltage() level

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Guaranteed Backup Min Operating Voltage t V relaxation previous charge Learning discharge (~1-2%) charge back relaxation

End-of-Service Determination

Learning Pulses

– Triggered discharge of C/100 ~ C/10 for a fixed time duration (~1-2% of capacity) – Battery voltage measured during discharge and after battery is relaxed – Pulses triggered at periodic intervals – Effective resistance of cell (Rcell) calculated from each pulse capture using difference in Battery Voltage and Learning Pulse load current – Two methods may be used to detect EOS

• By direct resistance monitoring called Direct Resistance Decisioning (DRD)
• By cell resistance trend called Resistance Slope Decisioning (RSD)

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Guaranteed Backup Learning Pulse Min Operating Voltage t V

Change in Resistance Vs Age

Nominal profile shown There are cell, chemistry and temperature variations leading to different resistance profile between regions Relationship between R and Aging is a function of cycle count and time

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End-of-Service Determination

Using C/10 current pulses

Experimental Data

End-of-Service Determination

• Direct Resistance Decisioning (DRD)

– Change in Resistance is computed using multiple Learning Pulses over timed intervals (~days to weeks) – Increase in resistance versus baseline resistance provides indication of cell approaching end of usable service – The degradation of R should be linear until SOH has degraded by 30 to 40% – Provides additional information the system can leverage

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End-of-Service Determination

• Resistance Slope Decisioning (SRD)

– Resistance rate of change (dR/dt) computed using multiple Learning Pulses over timed intervals (~weeks to monthly) – Included as secondary EoS determination technique – The degradation of R should be linear until SOH has degraded by 30 to 40% – Increase in dR/dt versus baseline rate provides indication of cell approaching end of usable service

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bq34110

Gas Gauge for Rarely Discharged Applications

CEDV Fuel Gauge Only for Li

• Ion, Polymer and

LiFePO4, NiMH and PbA. End

• of-Service Determination Function for Rarely

Discharged Applications WHr

• Charging Algorithm for Target Energy Capacity

Supports currents up to +/

• 32A, higher with scaling

Suitable for packs

• 2.5V to ~65V, higher with scaling

Low Operating Current of <

• 140uA with <64uA in Sleep

External

• 103AT NTC Thermistor Supported

Two

• wire (I2C) Communication

Configurable Alert / Warning Outputs

• 14
• pin TSSOP
• Very simple setup configuration
• Accurate fuel gauging
• Independent of protection solution and cell

balancing requirements

• Capable of gauging very high series cell batteries
• Enterprise Server Backup
• Telecommunications Backup
• Emergency Power Support
• UPS

Features Benefits Applications

VEN 1 ALERT1 LEN BAT CE REGIN REG25 14 SDA SCL ALERT2 TS SRN SRP VSS 100 0.1uF 2 3 4 5 6 7 13 12 11 10 9 8 0.1uF 100 0.1uF .01 75ppm 1uF 10k NTC REG25 REG25 PACK+ PACK- CHIP ENABLE I2C CLK I2C DATA /ALERT2 REGIN 10k 10k REGIN RLEN /ALERT1 0.1uF A VEN/GPIO

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Simplified Single-cell System Diagram

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VEN 1 ALERT1 LEN BAT CE REGIN REG25 14 SDA SCL ALERT2 TS SRN SRP VSS 100 0.1uF 2 3 4 5 6 7 13 12 11 10 9 8 0.1uF 100 0.1uF .01 75ppm 1uF 10k NTC REG25 REG25 PACK+ PACK- CHIP ENABLE I2C CLK I2C DATA /ALERT2 REGIN 10k 10k REGIN RLEN /ALERT1 0.1uF A VEN/GPIO

Simplified Multi-cell System Diagram

33 VEN 1 ALERT1 LEN BAT CE REGIN REG25 14 SDA SCL ALERT2 TS SRN SRP VSS 100 0.1uF 2 3 4 5 6 7 13 12 11 10 9 8 0.1uF 100 0.1uF .01 75ppm 1uF 10k NTC REG25 REG25 PACK+ PACK- CHIP ENABLE I2C CLK I2C DATA /ALERT2 REGIN 10k 10k REGIN n series cells RLEN /ALERT1 0.1uF 0.1uF 100 100 100 100

Thank You