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Introduction to Battery Management Part 1: Battery Technology Overview Maria Cortez Upal Sengupta 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™ Introduction to Battery Management Part 1: Battery Technology Overview 3 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 Rechargeable Battery Options • Lead Acid • NiCd Volumetric energy density (Wh/L) ↑ 100 years of fine service! ↓ Heavy, low energy density, toxic materials ↑ High cycle count, low cost ↓ Toxic heavy metal, low energy density 600 • NiMH ↑ Improvement in capacity over NiCd ↓ High self-discharge 500 Li-ion 400 Lipolymer 300 • Lithium Ion / Polymer Ni-MH 200 Ni-Cd 100 Lead Acid 0 0 50 100 150 Gravimetric energy density (Wh/kg) 200 ↑ High Energy density, low self-discharge ↓ Cost, external electronics required for battery management Battery Chemistry Comparison Lead Acid NiCd • High Power, standby apps • Car battery, EV, UPS (+) (-) NiMH • High Power, long usage • Consumer electronics, electronic bikes, power tools + Li-Ion • High Capacity, long usage • Consumer electronics, cameras, some industrial applications • High Capacity, long usage • Video cameras, digital cameras, mobile phones, PC / tablets (-) (+) (-) (+) (-) Simple & low cost (lowest $/kWH) Low Specific Energy – poor energy / weight ratio Fast & simple charging Low specific energy 30-40% more capacity vs. NiCd Limited cycle life – reduced w/ deep discharge High Energy density Requires protection circuit Mature & well understood Slow charge (up to 14 hours) Good cycle life & shelf life Memory effect Simple storage & transport Complex charge algorithm Relatively low selfdisch. Subject to aging (even if not used) High Discharge Currents Toxic materials Good load performance over temperature Toxic - not environment ally friendly Environmentally “friendlier” Poor overcharge tolerance Low maintenance Transport regulations when shipping in high volumes Low Self Discharge Limited cycle life, reduced w/ deep cycling Economical High self discharge Nickel content makes recycling profitable Generates heat at high discharge No memory Simple storage & transport Toxic materials High self discharge – worse @ high temp No periodic discharge needed Low temp performance 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 18650 Li-Ion Cell Capacity Development Trend 3500 18650 Cell 8% 2500 2000 65mm Cell Capacity mAh 3000 1500 1000 500 0 1990 1994 1998 2002 2006 2010 • 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 18mm 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 What is Battery Management? • Battery management circuits – – – – Control charge flow into battery Prevent abuse conditions Monitor critical parameters Communicate information • 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. Pack Configurations +7.2V Series +3.6V +7.2V +3.6V 2s3p 7.2V 1s3p 3.6V 1s2p configuration Parallel 2s1p Li-Ion Battery Management Components SPI or I2C PMIC System Host SMPS AC Adapter DC- 3 V / 5V Chemical Fuse Pack+ DC+ Charger IC 1-4 Cells Host Controlled SMBus or Stand Alone System Rails Multi-Rail Fuel Gauge IC CLK I2C / SMBus DATA Temp Protection Over /Under Voltage Temp Sensing Gauging Charge Control Authentication Chg Dsg AFE IC VCELL1 Analog Interface Over Current Cell Balancing VCELL2 Voltage ADC Current ADC Pack- Secondary Safety Over Voltage Protection IC (Optional) Sense Resistor Li-Ion Battery Pack Li-Ion 18650 Discharge at Various Rates V1 V2 Self-heating Effect Lowers the Internal Impedance V = I × RBAT 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 Effect of Impedance Increase on Runtime Battery Voltage (V) 4.5 Fresh Battery Aged Battery with 100 Cycles 4.0 3.5 3.0 0 0.5 1.0 Time (h) 1.5 2.0 • Change of no-load capacity during 100 cycles < 1% • Also, after 100 cycles, impedance doubles • Double impedance results in 7% decrease in runtime Charge Voltage Affects Battery Service Life 1100 Cell Capacity (mAh) 1000 900 4.2 V 800 700 600 4.3 V 500 400 4.35 V 0 100 200 300 400 Number of Cycles 4.25 V 500 600 • 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 Recoverable Capacity (%) Shelf-life, Degradation without Cycling 200C at 4.1 V 100 200C at 4.2 V 80 60 600C at 4.1 V 40 600C at 4.2 V 20 0 1 3 5 7 Months 9 11 13 • 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 Source: M. Broussely et al at Journal of Power Sources 97-98 (2001) Charge Current versus Battery Degradation Cell Capacity (mAh) 900 1.0C 800 1.1C 1.3C 1.5C 700 600 500 2.0C 0 100 200 300 400 Number of Cycles 500 600 • 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 There are many variations of “Li-Ion” Batteries! Cathode Material (LI+) Li CoO2 Li Mn2O4 Li FePO4 Anode Material Li NMC Li NCA Li CoO2 NMC Li MnO NMC Graphite Li -CoO2 Li -CoO2 Hard Carbon LTO (“Titanate”) Vmax 4.20 4.20 3.60 4.20 4.20 4.35 4.20 4.20 2.70 Vmid 3.60 3.80 3.30 3.65 3.60 3.70 3.75 3.75 2.20 Vmin 3.00 2.50 2.00 2.50 2.50 3.00 2.00 2.50 1.50 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 Energy Cells, Power Cells, and “Mid-Rate” Cells for different applications… “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 “Standard” LiCoO2 vs. LiFePO4 Cell Voltage 4.2 4.03 3.86 Li-Cobalt Voltage, V 3.69 3.52 3.35 3.18 Li-Iron-Phosphate 3.01 2.84 2.67 Depth of Discharge 2.5 0 20 40 60 DOD, % 80 100 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 Introduction to Battery Management Introduction to Battery Management Maria Cortez Upal Sengupta Introduction to Battery Management Part 2: Battery Monitoring / Gauging Battery Monitoring / Gauging What 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 63% – Temperature – Remaining battery capacity information • Capacity percentage • Run time to empty/full • Talk time, idle time, etc. – Battery State of Health – Battery safety diagnostics Run Time 6:27 Basic Smart Battery System CHG DSG VPACK Vbatt ICHG comm Gas Gauge Tbatt Battery Model VDSG Load Charger VCHG IDSG Rs qk q 0 t k I k Ibatt Gauging Battery Chemical Capacity (Qmax) Definitions: Li-Ion Discharge Profile • Battery Capacity = “1C” 1C Discharge rate is current to 4.5 completely discharge a battery in one hour Example: • 2200mAh battery • 1C discharge rate = 2200mA @ 1 hr • 0.5C rate: 1100mA @ 2hrs Voltage, V Load current: < 0.1C 4.0 3.6V (Battery rated voltage) 3.5 EDV = 3.0V/cell 3.0 0 1 2 3 4 Capacity, Ah Battery Model CBAT RBAT 5 Qmax 6 • 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 Gauging Useable Capacity “QUSE” 4.2 Open Circuit Voltage (OCV) I•RBAT 3.6 Battery Voltage (V) Qmax Quse Cell voltage under load 3.0 EDV 2.4 Quse • EDV will be reached earlier for higher discharge current. • Useable capacity Quse < Qmax Qmax + + - I RBAT OCV V = OCV - I*RBAT - Gauging Types of Gauging Algorithms… Impedance Track™ Cell Voltage Measurement • Measures cell voltage • Advantage: Simple • Not accurate over load conditions • Directly measures effect of discharge rate, temp, age and other factors by learning cell impedance • Calculates effect on remaining capacity and full charge capacity Coulomb Counting • • • • • • • Measures and integrates current over time Affected by cell impedance Affected by cell self discharge Standby current Cell Aging Must have full 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 • No learning cycles needed • No host algorithms or calculations Gauging Simple Measured Cell Voltage - Effect of IR drop 4.2 Battery Voltage (V) Open-Circuit Voltage (OCV) 3.9 I × RBAT 3.6 3.3 3.0 EDV Battery Capacity QUSE QMAX ISSUES: • 25% granularity • First bar lasts many times longer then subsequent bars • No compensation for cell age • Less run time - I + OCV R • Two bars represents over 50% capacity between 3.8 and 3.4 V V=OCV - I*R + • Pulsating load varies capacity bar up and down V VOCV I R BAT ? • Accurate ONLY at very low current BAT BAT Gauging - Coulomb Counting Li-Ion Battery Cell Voltage 4.5 0.2C Discharge Rate 4.0 • Measure and Integrates Charge • Current sensed w/ resistive shunt Q 3.5 3.0 Q i dt EDV = End of Discharge Voltage EDV 0 1 • Use this combined with OCV to relate battery Charge (mAH) to battery DOD (%) and battery Voltage (V) 2 3 Capacity, Ah 4 5 Qmax ISSUE: Internal battery resistance is variable - cell impedance changes with… • Current • Voltage • Time • Temperature 6 Gauging Coulomb Counting - Learning before Fully Discharged ISSUES: 4.5 – 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 Voltage (V) 4 EDV2 3.5 7% EDV1 3% EDV0 3 0 0% 1 2 3 Capacity Q (Ah) 4 5 6 • Remaining capacity depends on current, temperature, and impedance 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 how much the battery can still deliver under all conditions, needs capacity learning. – Not suitable for high variable load current – Uses processor resources for gauging computations Gauging Impedance Track™ gas gauge • Incorporates Voltage-based gauge: Accurate gauging under no load Coulomb counting: Accurate gauging under load 13 Real-time impedance update Remaining run-time calculation 12 Safety and State of Health • Updates impedance at every cycle voltag e, V – – – – – R BAT OCV OCV VBAT 11 IR I AVG Voltage under load (a) • Uses impedance, discharge rate, and temperature information to calculate rate/temperature adjusted FCC (Full Charge Capacity) V = OCV(SOC, T) – I × RBAT (SOC, T) 9 10 0 80 10 0 OCV IR Voltage under load 10 4.5 10 Voltage Under Load 9 (a) 20 3.5 3 0.13 0.13 0.1 0 4 0 (b) R, Ohm 11 11 Resistance () OCV Voltage, V voltag e, V Voltage (V) IR 12 12 0.15 40 60 SOC, % 0.15 0.15 13 13 9 20 0 40 60 SOC, % 80 10 0 20 20 40 40 60 60 SOC (%) SOC, % 80 80 100 100 Gauging OCV - Voltage lookup • One can tell how much water is in a glass by reading the water level mL marks – Accurate water level reading should only be made after the water settles (no ripple, etc) I(t) • 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) q (t ) V(t) • OCV measurement allows SOC estimation • Relaxation time varies depending on: • SOC, • Prior load rate • Temperature Open Circuit Voltage (OCV) Comparison of OCV Profiles for 5 Manufacturers • OCV profiles similar for all tested manufacturers, using same chemistry 4.20 3.93 • Average SOC prediction error based on OCV – SOC correlation is about 1% 3.67 3.40 100% 50% • Same database can be used with batteries produced by different manufacturers as long as cell chemistry is the same 0% +10 SOC Error (%) Voltage Deviation (mV) State of Charge (SOC) 0 -10 100% +2.6 • TI maintains OCV profile data for many different cell types (“Chemical ID” table) +1.3 0 -1.3 -2.6 50% 0% 100% 50% 0% Learning Qmax without Full Discharge Cell Voltage (V) 4.2 4.1 Start of Discharge Start of Charge 4.0 P1 P2 Q P1 Q 3.9 OCV Measurement Points OCV 3.8 Measurement Points 0 0.5 1.0 1.5 2.0 2.5 3.0 Time (hour) 0 P2 0.5 1.0 1.5 2.0 2.5 3.0 Time (hour) • 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 Q Qm ax SOC1 SOC 2 Z-track Accuracy in Battery Cycling Test Remaining Capacity Error, % 1 0.5 • Error is shown at 10%, 5% and 3% points of discharge curve • For all 3 cases, error stays below 1% during entire 250 cycles 0 0.5 1 1.5 0 50 100 150 Cycle Number error at 10% error at 5% error at 3% 200 250 300 Introduction to Battery Management Introduction to Battery Management Part 3: Li-Ion Battery Charging 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 Review: “Ideal” Li-Ion CC-CV Charge Curve “CV” “CC” Practical “CC-CV” – allows for fault conditions Pre-charge (Trickle Charge) Fast-charge (Constant Current) VOREG ICHARGE Constant Voltage Battery Pack Voltage Taper Current VPrecharge ~3.0V VShort ~2.0V IPrecharge ITERM IShort Fast Charge (PWM charge) CCCV - From an actual data sheet… Charge Voltage Accuracy vs. Cycle Life • +/- 50mV on each charge cycle +/- 100 cycles to the same point of degradation! 4.2V 4.3V 4.35V 4.25V 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 Charging from a Current-Limited Source • USB port limited to 500mA • But… w/ Switching charger, can charge > 500 mA 500 mA ICHG =? USB VBAT + VIN Charge Controller Charger • • • • • 500-mA Current Limit 40% more charge current with switcher Full use of USB Power Shorter charging time Higher efficiency, lower temperature Charge Current (A) 1 0.9 Switching Charger 0.8 0.7 0.6 Linear Charger 0.5 0.4 2.4 2.6 2.8 3 ICHG_sw= 3.2 3.4 3.6 3.8 Battery Voltage (V) 4 VIN • η • 500mA VBAT 4.2 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 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 Simplicity vs. Flexibility, or HW vs. SW • Standalone charger: – HW controlled – Set critical parameters with resistors or pullup/pulldowns – Fixed functionality Host – Controlled Charger • Can adjust charge voltage, current limits, timer settings, etc. “on the fly” with software • Adaptable to different cell types or application needs • Allows more detailed read-back of fault conditions (overtemp, timer limit, input voltage, etc.) Summary – Battery Charging • First charger selection criteria – “volts and amps” like any power supply requirement • Consider additional requirements unique to the battery type you are using • Consider other application requirements to decide if you should use power path system, standalone charger, or host-controlled charger • See additional appnotes and “E2E Forum” at www.ti.com/battery Introduction to Battery Management Introduction to Battery Management Part 4: Special Considerations for larger battery packs The basic functions of all pack monitoring circuits are the same… • 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 However… • There are some significant differences! Newer Applications = More Cells • New applications with higher series cell counts • Typically 8- to 16-series cells for a centralized system and 17- to 200-series cells for a distributed system • Higher voltages, and higher currents • Additional challenges in applications such as Power Tools, EBikes, Electric & Hybrid Vehicles, UPS Systems, etc. New Application Challenges • Very High Currents – Can be High on Discharge, Low on Charge • Uneven self-heating of cells on Discharge = Imbalance – Load and Battery Physically Separated • Ex: String Trimmer - Motor 3 feet away - inductive spikes • Separate Charge & Discharge Paths – Allows protection pass element (MOSFET) to be sized to requirement • Load and Charger have unique connection to battery • Fast Transition between Charge & Discharge – Hybrid Electric Vehicles, UPS Systems "Big" Battery Challenges High Cell Count Battery Systems • Weakest link (cell) rules the pack • Physically larger battery pack so... ... Cells on the ends may see a larger temperature swings than others • More likely to become imbalanced • Higher cell count = Higher voltage = More catastrophic potential 8.5" ... More difficult to connect cells in order ... Cell connections more fragile (likely to break) ... Series cell break, remaining cells see full reverse stack voltage ... Shorted cell (>1P) fed by parallel cells 6.5" Source: Eagle-Picher at 27th International Battery Seminar & Exhibit (2010) Issues to consider • What level of functionality is required for battery management in a large pack? – Safety only? – Safety & Cell Balancing? – Safety, Cell Balancing, and Fuel Gauging? • Due to the sheer number of interconnections in a larger pack, a single-chip solution may not be practical • Design the a pack management system to meet the requirements (functionality vs. cost/complexity) Secondary / Redundant Protection • • • • Multicell packs may need secondary protection Backup system in case of catastrophic faults Simple – protect against worst case scenarios only Second protector thresholds set higher (e.g. overvoltage) than primary protector • System may or may not be recoverable (usable) after secondary fault Why balancing? • Failed battery - about 3 years old, perhaps 50 - 100 cycles • Run time was decreasing, eventually died • Case removed for construction inspection – Sturdy assembly – Electronics at end – Flex for temp & cell voltage • Potted circuit board – Unknown protection circuit (Not from TI!) – Discharge limiting FETs were OFF Picture of battery Failed battery cell voltages • Cell voltage check showed a single bad cell • What went wrong? – Open circuit cell with bias from electronics? – Cell forced into reverse voltage? • Would balancing have prevented this? Cell 6 (top) Voltage (mV) 4017 5 4018 4 4017 3 -536 2 4022 1 (bottom) 4023 Cell Balancing What Causes Imbalance? • Capacity variation (1~2% cellto-cell for same model) • Charging state difference (i.e. SOC difference) • Impedance variation (up to 15%) causes voltage difference when charging/discharging • Localized heat degrades cells faster than others, particular self-heating at high discharge rate Effects of unbalanced cells: • Reduced run-time due to... - Premature charge termination - Early discharge termination • Further cell abuse from cycling above or below optimal cell voltage limits 4.4 Overcharge 4.2 4.0 3.8 Undercharge 3.6 3.4 High Cell Count battery systems are more likely to see imbalance due to temperature gradients and cell selfheating at high discharge rates. Capacity Under-used 3.2 3.0 Time 2 4 6 8 10 Cell Balancing Circuits • Linear Cell Bypass / “Bleed Balancing” • Active / Switch Mode: – Switch mode energy transfer from cell to cell – Allows higher balance current with less heat – More expensive and complex to implement – used only for very large / high capacity applications – Linear / dissipative – low current – Most common implementation for small and medium size battery packs PACK + V3 1 k R1 Q1 R5 Q2 Battery Monitor / Balance Controller CELL 2 V2 1 k R2 2 CELL 1 1 k R3 R4, R5 << Rdson Q2 R4 Q1 Rdson 1 V1 R Active / Switch Mode There are many variations of “Li-Ion” Batteries! Cathode Material (LI+) Li Li CoO2 MnO Li FePO4 Anode Material Li NMC Li NCA Li CoO2 NMC Li MnO NMC Graphite Li CoO2 Li -CoO2 Hard Carbon LTO (“Titanate”) Vmax 4.20 4.20 3.60 4.20 4.20 4.35 4.20 4.20 2.70 Vmid 3.60 3.80 3.30 3.65 3.60 3.70 3.75 3.75 2.20 Vmin 3.00 2.50 2.00 2.50 2.50 3.00 2.00 2.50 1.50 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 Can the battery management circuit handle the different chemical variations? • Fuel Gauge: TI Impedance Track Gauges can be programmed with specific “Chemical ID” values to provide accurate monitoring of different types of batteries • Protectors: TI Precision Protectors are designed for a variety of OV / UV thresholds – Either user-programmable (EEPROM) or factory orderable options for specific levels “Pack-Based” Gauging for large packs • Smaller packs can have a single IC to monitor each individual cell, balance and gauge on a cellby-cell basis • This may not be practical for larger packs due to number of interconnections (and memory) required • bq2060A has been TI’s long-running solution for a generic pack-based gauge • bq34z100 family is the new generation of devices for this need o When used with Li-Ion type cells, cell balancing & individual cell OVP must be done externally see bq779xx family devices bq34z100 Example of typical implementation bq34z100 Li-Ion Pack Monitor bq78PL900 bq78PL910A bq77908A Protection and Balancing not required for NiXX, PbSO4, etc. The basic functions of all pack monitoring circuits are the same… • 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 Introduction to Battery Management Introduction to Battery Management Part 5: Introduction to Wireless Power bqTESLATM Wireless Power Solutions Wireless Power Consortium (WPC) Industry wide standard for delivering wireless power up to 5W Aimed to enable interoperability between various charging pads and portable devices Standard continues to gain traction with increasing list of members (105+) Compatible devices will be marked with a Qi logo and more… Qi: Intelligent Control of Inductively Coupled Power Transfer • Power transmitted through shared magnetic field – Transmit coil creates magnetic field – Magnetic field induces current in receiver coil – Shielding material below TX and above RX coils • Power transferred only when needed – Transmitter waits until its field has been perturbed – Transmitter sends seek energy and waits for a digital response – If response is valid, power transfer begins • Power transferred only at level needed – Receiver constantly monitors power received and delivered – Transmitter adjusts power sent based on receiver feedback – If feedback is lost, power transfer stops I z<D D Factors Affecting Coupling Efficiency • Coil Geometry – Distance (z) between coils – Ratio of diameters (D2 / D) of the two coils ideally D2 = D – Physical orientation • Quality factor – Ratio of inductance to resistance – Geometric mean of two Q factors • Near field allows TX to “see” RX • Good Efficiency when coils displacement is less than coil diameter (z << D) Factors Affecting Coupling Efficiency Optimal operating distance 40% at 1 diameter 1% at 2.5 diameter 0.1% at 4 diameters 0.01% at 6 diameters bq50k + bq51K: Qi-Compliant Solution Power Communication / Feedback Communication - Basics • Primary side controller must detect that an object is placed on the charging pad. – When a load is placed on the pad, the primary coil effective impedance changes. – “Analog ping” occurs to detect the device. • After an object is detected, must validate that it is WPC-compatible receiver device. – “Digital Ping” – transmitter sends a longer packet which powers up the RX side controller. – RX side controller responds with signal strength indicator packet. – TX controller will send multiple digital pings corresponding to each possible primary coil to identify best positioning of the RX device. • After object is detected and validated, Power Transfer phase begins. – RX will send Control Error Packets to increase or decrease power level • WPC Compliant protocol ensures interoperability. Analog Ping with and without object on pad Vertical Scale: 20V/div Horizontal Scale: 20 uS/div (a) No object on pad (b) RX Device placed on pad Analog Ping / Digital Ping / Startup Analog Pings – no object detected Analog Ping – object detected. Followed by subsequent Digital Ping and initiation of communications functions TX COIL VOLTAGE Vertical Scale: 20V/div Horizontal Scale: 200 mS/div COMM Communication – How it works… Switching Frequency Variation • System operates near resonance for improved efficiency. • Power control by changing the frequency, moving along the resonance curve. • Modulation using the power transfer coils establishes the communications. • Feedback is transferred to the primary as error. Operating Point 80 KHz 100 KHz 120 KHz bqTesla System Efficiency Breakdown Measured from DC input of Transmitter to DC output of Receiver Tx Eff. Magnetics Eff. 100% Rx Eff. System Efficiency TX Eff RX Eff Magnetics Eff 90% Efficiency (%) 80% 70% System Eff 60% 50% 40% 30% 20% 0 0.5 1 1.5 2 2.5 Output Power (W) 3 3.5 4 4.5 5 bqTESLA EVMs bqTESLA Evaluation Modules New bq51013EVM-725 Qi-compliant coil used w/ EVM kit 40-mm x 30-mm x 0.75-mm WPC Compliant Receiver Coil WPC Compliant Transmitter Coil bq51013 “form factor” demo PCB (PR1041) 5 x 15 mm footprint for all RX side circuitry • Represents what an OEM would design into their actual end-product to enable wireless power from a QI-compliant charging pad. Wireless Power Transmitter – App Note • Title, “Building a Wireless Power Transmitter” • Detailed Discussions on: – Critical Design Parameters – Layout Requirements – Component Requirements – Example Waveforms – Most Common Pitfalls for Qi Certification • TI Wireless Power Web Page http://www.ti.com/wirelesspower (http://www.ti.com/litv/pdf/slua635) TI Wireless Power Forum • TI E2E Community-Wireless Power http://e2e.ti.com/support/power_management/wireless_power/default.aspx • External Forum—available for entire engineering community • Ground Rules – Keep the questions technical in nature, good question your peers can benefit from at a later date. – One question per-post to make it easer to search. – Place P/N in Topic with description of question again to make it easier to search. – Refer to your TI Sales Rep for pricing & delivery questions For technical specs & tutorials: http://www.wirelesspowerconsortium.com