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  1. Introduction to Battery ManagementPart 1: Battery Technology Overview UpalSengupta Maria Cortez

  2. INTRODUCTION TO BATTERY MANAGEMENT • Part 1: Battery Technology Overview • Part 2: Battery Gauging, Cell Balancing, and Protection • Part 3: Li-Ion Battery Charging • Part 4: Special Considerations for Large Battery Packs • Part 5: Intro to Wireless Power and bqTESLA™

  3. Introduction to Battery Management Part 1: Battery Technology Overview

  4. Intro to Battery Management – Part 1 Basic comparison of rechargeable batteries Li-Ion Battery Performance Characteristics New types of Li-Ion batteries optimized for diverse applications Basic requirements for / functions of battery management

  5. Rechargeable Battery Options Lead Acid 100 years of fine service! Heavy, low energy density, toxic materials • NiCd • High cycle count, low cost • Toxic heavy metal, low energy density • NiMH • Improvement in capacity over NiCd • High self-discharge • Lithium Ion / Polymer • High Energy density, low self-discharge • Cost, external electronics required for battery management

  6. Battery Chemistry Comparison

  7. Why is Li-Ion popular? A high performance battery for high performance devices! Gravimetric energy density  High Capacity, Light weight battery Volumetric density energy  High Capacity, Thin battery Low self-discharge  Stays charged when not in use

  8. 65mm 18mm 18650 Li-Ion Cell Capacity Development Trend 18650 Cell 8% Cell Capacity mAh • 18650: Cylindrical, 65mm length, 18mm diameter • 8% yearly capacity increase over last 15 years • Capacity increase has been delayed from 2010 • Li-Ion Battery Tutorial, Florida battery seminar

  9. Cell Construction and Safety Safety Elements Aluminum or steel case Pressure relief valve PTC element Polyolefin separator Low melting point (135 to 165°C) Porosity is lost as melting point is approached Stops Li-Ion flow and shuts down the cell Recent incidents traced to metal particles that pollutes the cells and creates microshorts

  10. What is Battery Management? • Battery management circuits • Control charge flow into battery • Prevent abuse conditions • Monitor critical parameters • Communicateinformation • Systems require battery management to extend run-times, maximize safety, and maximize battery-life • Degrees of implementation vary, but sophisticated battery management consists of three components : Battery Charge Mgmt, Battery Gauge / Mgmt, and Protection. 1s2p configuration Pack Configurations +3.6V +7.2V +7.2V 1s3p 3.6V +3.6V Series 2s3p 7.2V Parallel 2s1p

  11. Li-Ion Battery Management Components SPI or I2C System Host PMIC Multi-Rail System Rails SMPS 3 V / 5V Chemical Fuse Dsg Chg Pack+ Charger IC 1-4 Cells Host Controlled SMBus or Stand Alone DC+ AC Adapter Fuel Gauge IC CLK DC- Secondary Safety Over Voltage Protection IC (Optional) AFE IC VCELL1 I2C / SMBus • Protection • Over /Under Voltage • Temp Sensing • Gauging • Charge Control • Authentication Analog Interface Over Current Cell Balancing VCELL2 DATA Temp Sense Resistor Voltage ADC Current ADC Pack- Li-Ion Battery Pack

  12. Li-Ion 18650 Discharge at Various Rates V1 V2 Self-heating Effect Lowers the Internal Impedance V = I × RBAT

  13. Li-Ion 18650 Discharge at Various Temperatures • Organic electrolyte makes internal resistance of Li-Ion battery more temperature dependent than other batteries Self-heating Effect Lowers the Internal Impedance

  14. Effect of Impedance Increase on Runtime 4.5 4.0 3.5 3.0 Fresh Battery Aged Battery with 100 Cycles Battery Voltage (V) 0 0.5 1.0 1.5 2.0 Time (h) • Change of no-load capacity during 100 cycles < 1% • Also, after 100 cycles, impedance doubles • Double impedance results in 7% decrease in runtime

  15. Charge Voltage Affects Battery Service Life 1100 1000 900 800 700 600 500 400 4.2 V Cell Capacity (mAh) 4.3 V 4.25 V 4.35 V 0 100 200 300 400 500 600 Number of Cycles • The higher the voltage, the higher the initial capacity • Overcharging shortens battery cycle life Source: “Factors that affect cycle-life and possible degradation mechanisms of a Li-Ion cell based on LiCoO2,” Journal of Power Sources 111 (2002) 130-136

  16. Shelf-life, Degradation without Cycling If battery sits on the shelf too long, capacity will decrease Degradation accelerates at higher temperatures and voltages Depending on chemistry, there are specific recommendations for best storage conditions 100 80 60 40 20 0 200C at 4.1 V 200C at 4.2 V Recoverable Capacity (%) 600C at 4.1 V 600C at 4.2 V 1 3 5 7 9 11 13 Months Source: M. Broussely et al at Journal of Power Sources 97-98 (2001)

  17. Charge Current versus Battery Degradation 900 800 700 600 500 1.0C 1.1C 1.3C Cell Capacity (mAh) 1.5C 2.0C 0 100 200 300 400 500 600 Number of Cycles • Charge Current: Limited to 1C rate to prevent overheating that can accelerate degradation • Some new cells can handle higher-rate Source: “Factors that affect cycle-life and possible degradation mechanisms of a Li-Ion cell based on LiCoO2,” Journal of Power Sources 111 (2002) 130-136

  18. There are many variations of “Li-Ion” Batteries! • Typical Anode and Cathode Materials used for Li-Ion Cells • All the above cells are considered “Li-Ion” • In addition to the different voltage ranges shown, they will also have different capacity, cycle life, and charge/discharge rate performance (not shown) • Specific performance parameters can be optimized based on chemistry and physical design of a cell – the “important” parameters depend on the application

  19. Energy Cells, Power Cells, and “Mid-Rate” Cells for different applications…

  20. “What’s Important” in various applications Vehicle Starter Application: Extremely high surge current  need very low cell internal resistance Must work at all extremes of temperature Battery discharge is very brief – spend > 99% of time being recharged Battery is rarely (ideally, “never”) fully discharged  cycle life is not important Power Tool Application: Frequent, fast discharge use  need low resistance and fast recharge Rugged, durable cells are desirable “Green” trend replaces NiCd with Li-Ion  DIFFERENT TYPE OF LI-ION than in phone & notebook PC applications, optimized for high current usage requires different type of charging & monitoring circuits! Small Handheld Devices: Light weight and small size are critical High energy capacity for longest possible run time Accurate capacity monitoring is important – especially for smartphones

  21. “Standard” LiCoO2 vs. LiFePO4 Cell Voltage Li-Cobalt Li-Iron-Phosphate Depth of Discharge

  22. Summary – Battery Management The basic functions of all Li-Ion pack monitoring circuits are the same regardless of the application Maintain safe operation of the battery pack under all conditions Extend / maintain service life of the battery as much as possible Ensure complete charging and utilization of the pack without violating safety thresholds The level of sophistication / features implemented will vary depending on the application Performance / Cost tradeoffs Criticality of safety & accuracy requirements Physical size and energy capability

  23. Introduction to Battery Management

  24. Introduction to Battery Management UpalSengupta Maria Cortez

  25. Introduction to Battery Management Part 2: Battery Monitoring / Gauging

  26. Battery Monitoring / GaugingWhat is Fuel Gauging Technology? Fuel Gauging = technology to report battery operational status and predict battery capacity under all system active and inactive conditions. Key benefits are providing extended RUN TIME and LIFE TIME! The Gas Gauge function autonomously reports and calculates: • Voltage • Charging or Discharging Current • Temperature • Remaining battery capacity information • Capacity percentage • Run time to empty/full • Talk time, idle time, etc. • Battery State of Health • Battery safety diagnostics 63% Run Time 6:27

  27. Basic Smart Battery System CHG DSG VPACK Vbatt ICHG VCHG VDSG Gas Gauge comm Tbatt Battery Model Load Charger IDSG Ibatt Rs

  28. 4.5 4.0 CBAT RBAT 3.5 3.0 0 GaugingBattery Chemical Capacity (Qmax) • Definitions: • Battery Capacity = “1C” • 1C Discharge rate is current to completely discharge a battery in one hour • Example: • 2200mAh battery • 1C discharge rate = 2200mA @ 1 hr • 0.5C rate: 1100mA @ 2hrs • Battery Capacity (Qmax): Amount of charge can be extracted from the fully charged cell to the end of discharge voltage (EDV). • EDV (End of Discharge Voltage): Minimum battery voltage acceptable for application or for battery chemistry Li-Ion Discharge Profile Load current: < 0.1C 3.6V (Battery rated voltage) Voltage, V EDV = 3.0V/cell Battery Model 1 2 3 4 5 6 Qmax Capacity, Ah

  29. - + I RBAT OCV V = OCV- I*RBAT - + Gauging Useable Capacity “QUSE” 4.2 Qmax Quse Open Circuit Voltage (OCV) I•RBAT 3.6 Cell voltage under load Battery Voltage (V) 3.0 EDV 2.4 Quse Qmax • EDV will be reached earlier for higher discharge current. • Useable capacity Quse < Qmax

  30. GaugingTypes of Gauging Algorithms… • Impedance Track™ • Directly measures effect of discharge rate, temp, age and other factors by learning cell impedance • Calculates effect on remaining capacity and full charge capacity • No learning cyclesneeded • No host algorithms or calculations Cell Voltage Measurement • Measures cell voltage • Advantage: Simple • Not accurate over load conditions Coulomb Counting • Measures and integrates current over time • Affected by cell impedance • Affected by cell self discharge • Standby current • Cell Aging • Must havefull to empty learning cycles • Must develop cell models that will vary with cell maker • Can count the charge leaving the battery, but won’t know remaining charge without complex models • Models will become less accurate with age

  31. - + I RBAT OCV V=OCV- I*RBAT - + GaugingSimple Measured Cell Voltage - Effect of IR drop 4.2 ISSUES: • 25% granularity • First bar lasts many times longer then subsequent bars • No compensation for cell age • Less run time • Two bars represents over 50% capacity between 3.8 and 3.4 V • Pulsating load varies capacity bar up and down • Accurate ONLY at very low current Open-Circuit Voltage (OCV) 3.9 I × RBAT 3.6 Battery Voltage (V) 3.3 EDV 3.0 Battery Capacity QUSE QMAX ?

  32. Li-Ion Battery Cell Voltage 4.5 0.2C Discharge Rate 4.0 Q 3.5 EDV 3.0 0 1 2 3 4 5 6 Capacity, Ah Qmax Gauging - Coulomb Counting • Measure and Integrates Charge • Current sensed w/ resistive shunt • Use this combined with OCV to relate battery Charge (mAH) to battery DOD (%) and battery Voltage (V) EDV = End of Discharge Voltage ISSUE: Internal battery resistance is variable - cell impedance changes with…

  33. GaugingCoulomb Counting - Learning before Fully Discharged 4.5 ISSUES: • Too late to learn when 0% capacity is reached • How to learn if EDV thresholds aren’t reached? • A set voltage threshold for given percentage of remaining capacity • True voltage at 7%, 3% EDV • Remaining capacity depends on current, temperature, and impedance 4 Voltage (V) EDV2 7% 3.5 EDV1 3% EDV0 0% 3 • DISADVANTAGES: • New full capacity must be learned over time (full chg/dsg cycle) • Learning cycle needed to update Qmax • Battery capacity degradation with aging (Qmax Reduction: 3 – 5% with 100 cycles) • Gauging error increases 1% for every 10 cycle without learning • End of discharge points not compensated • Counting capacity out of battery doesn’t tell howmuch the battery can still deliverunder all conditions, needs capacity learning. • Not suitable for high variable load current • Uses processor resources for gauging computations 0 1 2 3 4 5 6 Capacity Q (Ah)

  34. GaugingImpedance Track™ gas gauge • Incorporates • Voltage-based gauge: Accurate gauging under no load • Coulomb counting: Accurate gauging under load • Real-time impedance update • Remaining run-time calculation • Safety and State of Health • Updates impedance at every cycle • Uses impedance, discharge rate, and temperature information to calculate rate/temperature adjusted FCC (Full Charge Capacity) V = OCV(SOC, T) – I × RBAT (SOC, T) 0.15 0.13 13 12 11 10 9 I  R OCV Resistance () Voltage (V) Voltage Under Load 0 20 40 60 80 100 SOC (%)

  35. GaugingOCV - Voltage lookup • One can tell how much water is in a glass by reading the water level • Accurate water level reading should only be made after the water settles (no ripple, etc) • One can tell how much charge is in a battery by reading well-rested cell voltage • Accurate voltage should only be made after the battery is well rested (stops charging or discharging) mL marks I(t) • OCV measurement allows SOC estimation • Relaxation time varies depending on: • SOC, • Prior load rate • Temperature V(t)

  36. Comparison of OCV Profiles for 5 Manufacturers 4.20 • OCV profiles similar for all tested manufacturers, using same chemistry • Average SOC prediction error based on OCV – SOC correlation is about 1% • Same database can beused with batteries produced by different manufacturersas long as cell chemistryis the same • TI maintains OCV profile data for many different cell types (“Chemical ID” table) 3.93 Open Circuit Voltage (OCV) 3.67 3.40 50% 0% 100% State of Charge (SOC) +2.6 +10 +1.3 SOC Error (%) 0 0 Voltage Deviation (mV) -1.3 -10 -2.6 100% 50% 0% 100% 50% 0%

  37. Change in capacity (mAH) is determined by exact coulomb counting Relative SOC1 and SOC2 are correlated with OCV after rest period Method works for both charge or discharge Learning Qmax without Full Discharge 4.2 4.1 4.0 3.9 3.8 Start of Discharge Start of Charge P1 P2 DQ Cell Voltage (V) DQ P1 OCV OCV P2 Measurement Points Measurement Points 0 0.5 1.0 1.5 2.0 2.5 3.0 Time (hour) 0 0.5 1.0 1.5 2.0 2.5 3.0 Time (hour)

  38. Z-track Accuracy in Battery Cycling Test • Error is shown at 10%, 5% and 3% points of discharge curve • For all 3 cases, error stays below 1% during entire 250 cycles

  39. Introduction to Battery Management

  40. Introduction to Battery Management Part 3: Li-Ion Battery Charging

  41. Introduction to Charging Concepts • Numerous ICs are available for charging Li-Ion batteries  • In order to choose the best device, the system designer needs to consider a number of factors beyond the simple power requirements associated with a given battery pack.  • This section will review some basic issues such as: • Li-Ion Charging Profile, and how charger accuracy can affect the service life of the battery • When to use a linear or switch-mode charger • The benefit of “power path management” in a system with an internal battery pack • When to use a host (microcontroller)-based charging scheme

  42. “CV” “CC” Review: “Ideal” Li-Ion CC-CV Charge Curve

  43. Practical “CC-CV” – allows for fault conditions Pre-charge (Trickle Charge) Fast-charge (Constant Current) Constant Voltage VOREG Battery Pack Voltage ICHARGE VPrecharge ~3.0V Taper Current VShort ~2.0V IPrecharge ITERM IShort Fast Charge (PWM charge)

  44. CCCV - From an actual data sheet…

  45. 4.2V 4.3V 4.25V 4.35V Charge Voltage Accuracy vs. Cycle Life • +/- 50mV on each charge cycle  +/- 100 cycles to the same point of degradation!

  46. Linear or Switch-Mode Charger… • Same type of decision as whether to use an LDO or a DC/DC converter • Low current, simplest solution  Linear Charger • High Current, high efficiency  Switch-Mode Charger • General Guideline ~ 1A and higher should use switching charger… or, if you need to maximize charge rate from a current-limited USB port

  47. Charging from a Current-Limited Source • USB port limited to 500mA • But… w/ Switching charger, can charge > 500 mA 1 500 mA ICHG =? 0.9 VBAT USB Switching Charger 0.8 + VIN 0.7 Charge Current (A) Charge Controller 0.6 Linear Charger Charger 0.5 • 500-mA Current Limit • 40% more charge current with switcher • Full use of USB Power • Shorter charging time • Higher efficiency, lower temperature 0.4 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 Battery Voltage (V) VIN VBAT • η•500mA ICHG_sw=

  48. Simplest Charger Architecture • Some possible concerns / issues: • What happens when battery is very low? • What happens if battery is missing or defective? • If system is operating, how can charger determine if battery current has reached a termination level? DC Source System Charger IC

  49. Power Path Management • Power supplied from adapter through Q1; Charge current controlled by Q2 • Separates charge current path from system current path; No interaction between charge current and system current • Ideal topology when powering system and charging battery simultaneously is a requirement

  50. Simplicity vs. Flexibility, or HW vs. SW • Standalone charger: • HW controlled • Set critical parameters with resistors or pullup/pulldowns • Fixed functionality