Introduction to Battery ManagementPart 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™

Part 1: Battery Technology Overview

3

Introduction to Battery Management

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↑ 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

0

100

200

300

400

500

600

0 50 100 150 200

Gravimetric energy density (Wh/kg)

Volu

met

ric e

nerg

y de

nsity

(Wh/

L)

Ni-MH

Li-ion

Li-polymer

Ni-Cd

Lead Acid

Battery Chemistry Comparison Lead Acid NiCd NiMH Li-Ion

• High Power, standby apps• Car battery, EV, UPS

• High Power, long usage• Consumer electronics, electronic

bikes, power tools

• 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 self-disch.

Subject to aging (even if not used)

High Discharge Currents

Toxic materials

Good load performance over temperature

Toxic - not environmentally friendly

Environment-ally “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

Low temp performance

Simple storage & transport

Toxic materials

High self discharge – worse @ high temp

No periodic discharge needed

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

• Li-Ion Battery Tutorial, Florida battery seminar

18650 Li-Ion Cell Capacity Development Trend

• 18650: Cylindrical, 65mm length, 18mm diameter• 8% yearly capacity increase over last 15 years• Capacity increase has been delayed from 2010

Cel

l Cap

acity

mA

h

18mm

65m

m

18650 Cell

0

500

1000

1500

2000

2500

3000

3500

1990 1994 1998 2002 2006 2010

8%

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

Series

Parallel

1s3p3.6V

+3.6V

2s3p7.2V

+7.2V

2s1p

+7.2V

1s2p configuration

+3.6V

Li-Ion Battery Management Components

Pack+

Pack-

Chemical Fuse DsgChg

SenseResistor

Secondary Safety

Over Voltage Protection IC

(Optional)Temp

I2C / SMBus

CLK

DATA

Li-Ion Battery Pack

Charger IC

1-4 CellsHost Controlled

SMBusor

Stand Alone

DC+

DC- VCELL1

VCELL2

System Rails

SPI or I2CPMIC

Multi-Rail

Fuel Gauge ICAFE IC

Analog InterfaceOver Current

Cell Balancing

ProtectionOver /Under VoltageTemp Sensing

GaugingCharge ControlAuthentication

Voltage ADCCurrent ADC

AC Adapter

SMPS 3 V / 5V

System Host

Li-Ion 18650 Discharge at Various Rates

V2

V1

V = I × RBAT

Self-heating Effect Lowers the Internal Impedance

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

• Change of no-load capacity during 100 cycles < 1%

• Also, after 100 cycles, impedance doubles

• Double impedance results in 7% decrease in runtime

0 0.5 1.0 1.5 2.0Time (h)

4.5

4.0

3.5

3.0

Fresh BatteryAged Battery with 100 Cycles

Bat

tery

Vol

tage

(V)

Charge Voltage Affects Battery Service 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

• The higher the voltage, the higher the initial capacity• Overcharging shortens battery cycle life

4.35 V

4.3 V4.25 V

4.2 V

0 100 200 300 400 500 600Number of Cycles

1100

1000

900

800

700

600

500

400

Cel

l Cap

acity

(mA

h)

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

Source: M. Broussely et al at Journal of Power Sources 97-98 (2001)

Rec

over

able

Cap

acity

(%)

1 3 5 7 9 11 13

100

80

60

40

20

0

Months

600C at 4.2 V600C at 4.1 V

200C at 4.2 V200C at 4.1 V

• Charge Current: Limited to 1C rate to prevent overheating that can accelerate degradation

• Some new cells can handle higher-rateSource: “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

Charge Current versus Battery Degradation

1.0C

1.1C1.3C

1.5C

2.0C

0 100 200 300 400 500 600Number of Cycles

900

800

700

600

500

Cel

l Cap

acity

(mA

h)

Cathode Material (LI+)

Li -CoO2

Li -Mn2O4

Li - FePO4

Li - NMC

Li - NCA

Li -CoO2 - NMC

Li - MnO - NMC

Li -CoO2 Li -CoO2

Anode Material

Graphite 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

There are many variations of “Li-Ion” Batteries!

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

0 20 40 60 80 1002.5

2.67

2.84

3.01

3.18

3.35

3.52

3.69

3.86

4.03

4.2

DOD, %

Vol

tage

, V

Li-Cobalt

Li-Iron-Phosphate

Depth of Discharge

Cell Voltage

“Standard” LiCoO2 vs. LiFePO4

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

Part 2: Battery Monitoring / Gauging

Introduction to Battery Management

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

Run Time 6:27

63%

Basic Smart Battery System

Batte

ry M

odel

GasGauge

RsIbatt

Vbatt

Load

Cha

rger

VCHG

ICHG

comm

CHG DSG

IDSG

VDSG

VPACK

Tbatt

k kk Itqq 0

GaugingBattery Chemical Capacity (Qmax)

Battery Model

CBAT RBAT

Definitions:• Battery Capacity = “1C”

1C Discharge rate is current to completely discharge a battery in one hourExample:• 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

EDV = 3.0V/cell

Qmax

Load current: < 0.1C

3.6V (Battery rated voltage)

1 2 3 4 5 60

3.0

3.5

4.0

4.5

Capacity, Ah

Vol

tag

e, V

Li-Ion Discharge Profile

• EDV will be reached earlier for higher discharge current.

• Useable capacity Quse < Qmax

RBATOCV

+ -I

+ -V = OCV - I*RBAT

GaugingUseable Capacity “QUSE”

QmaxQuse

4.2

3.6

3.0

2.4

Bat

tery

Vol

tage

(V

)

Open Circuit Voltage (OCV)

EDV

Qmax

I•RBAT

Quse

Cell voltage under load

GaugingTypes of Gauging Algorithms…

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 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

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 cycles needed

• No host algorithms or calculations

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 ?

4.2

3.3

3.0

Bat

tery

Vol

tage

(V

)

Open-Circuit Voltage (OCV)

EDV

Battery Capacity QMAXQUSE

3.9

OCV BATV V I R

I × RBAT

GaugingSimple Measured Cell Voltage - Effect of IR drop

RBATOCV+ - I

+ -V=OCV - I*RBAT

3.6

• 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)

dt iQ

EDV = End of Discharge Voltage

Q

0 1 2 3 4 5 6

3.0

3.5

4.0

4.5

Capacity, Ah

Li-Ion Battery Cell Voltage

EDV

Qmax

0.2C Discharge Rate

Gauging - Coulomb Counting

ISSUE: Internal battery resistance is variable - cell impedance changes with…

• Current • Voltage • Time • Temperature

GaugingCoulomb Counting - Learning before Fully Discharged

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

0 1 2 3 4 5 6

3

3.5

4

4.5

Vo

ltag

e (

V)

EDV00%

3%

7%

EDV1

EDV2

Capacity Q (Ah)

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

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)

BATBAT

AVG

OCV VR

I

0 20 40 60 80 1009

10

11

12

13

SOC, %

voltage, V

(a)

(b)

IR

OCV

Voltage under load

13

12

11

10

9

OCV

I R

Voltage Under Load

Vol

tage

(V

)

0 20 40 60 80 100

SOC (%)

0.15

0.13

0 20 40 60 80 100

0.1

0.13

0.15

SOC, %

R, O

hm

20 0 20 40 60 80 100 1202.5

3

3.5

4

4.5

SOC, %

Vol

tage

, V

(a)

(b)

IR

OCV

Voltage under load

Res

ista

nce

()

GaugingOCV - Voltage lookup

mLmarks

)(tq

V(t)

I(t)

• 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)

• OCV measurement allows SOC estimation

• Relaxation time varies depending on:• SOC, • Prior load rate• Temperature

Comparison of OCV Profiles for 5 Manufacturers

• 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)

0%50%

100% 0%50% 100% 0%50%

4.20

3.93

3.67

3.40Op

en

Circ

uit

Vo

ltag

e (

OC

V)

State of Charge (SOC)

+10

-10

Vo

ltag

e D

evi

atio

n (

mV

)

0

+2.6

-2.6

SO

C E

rro

r (%

)

0

+1.3

-1.3

100%

• 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

DQ

Cel

l Vol

tage

(V)

0 0.5 1.0 1.5 2.0 2.5 3.0Time (hour)

4.2

4.1

4.0

3.9

3.8

P1

P2

2SOC1SOC

QQ

max

Start of Charge

Measurement Points

OCV

0 0.5 1.0 1.5 2.0 2.5 3.0Time (hour)

DQ

P2

P1Start of Discharge

Measurement Points

OCV

Z-track Accuracy in Battery Cycling Test

0 50 100 150 200 250 3001.5

1

0.5

0

0.5

1

error at 10%error at 5%error at 3%

Cycle Number

Rem

aini

ng C

apac

ity

Err

or,

%

• Error is shown at 10%, 5% and 3% points of discharge curve

• For all 3 cases, error stays below 1% during entire 250 cycles

Introduction to Battery Management

Part 3: Li-Ion Battery Charging

Introduction to Battery Management

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

“CC”

“CV”

Practical “CC-CV” – allows for fault conditions

Fast Charge (PWM charge)

ITERM

VPrecharge~3.0V

ICHARGE

VOREG

Taper Current

Pre-charge(Trickle Charge)

Battery Pack Voltage

Constant VoltageFast-charge(Constant Current)

VShort~2.0V

IShort

IPrecharge

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!

4.35V

4.3V

4.25V

4.2V

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

USB

ChargeController

Charger

• 500-mA Current Limit• 40% more charge current with switcher• Full use of USB Power• Shorter charging time• Higher efficiency, lower temperature

ICHG =?500 mA

VBAT

+

VIN

VBATICHG_sw= • η • 500mA

VIN

Battery Voltage (V)

Ch

arg

e C

urr

en

t (A

)

2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.20.4

0.5

0.6

0.7

0.8

0.9

1

Linear Charger

Switching Charger

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?

Charger IC

DC Source System

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

Part 4: Special Considerations for larger battery packs

Introduction to Battery Management

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, E-

Bikes, 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

... More difficult to connect cells in order

... Cell connections more fragile (likely to break)• Higher cell count = Higher voltage = More

catastrophic potential... Series cell break, remaining cells see full

reverse stack voltage... Shorted cell (>1P) fed by parallel cells

Source: Eagle-Picher at 27th International Battery Seminar & Exhibit (2010)

8.5"

6.5"

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 Voltage (mV)

6 (top) 4017

5 4018

4 4017

3 -536

2 4022

1 (bottom) 4023

Cell Balancing

What Causes Imbalance?• Capacity variation (1~2% cell-

to-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

Time 2 4 6 8 10

4.4

4.2

4.0

3.8

3.6

3.4

3.2

3.0

Overcharge

CapacityUnder-used

Undercharge

High Cell Count battery systems are more likely to see imbalance due to temperature gradients and cell self-

heating at high discharge rates.

Cell Balancing Circuits• Linear Cell Bypass / “Bleed Balancing”

– Linear / dissipative – low current– Most common implementation for small and

medium size battery packs

V3

V2

V1

Q1

Q2

1

2

Active / Switch Mode

• 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

R4, R5 << Rdson

R5

Q2

R4

Q1

CELL 2

PACK +

1 k

1 kW

R2

R1

CELL 1

R

1 kW

R3

W

Rdson

Battery Monitor / Balance Controller

Cathode Material (LI+)

Li -CoO2

Li - MnO

Li - FePO4

Li - NMC

Li - NCA

Li -CoO2 - NMC

Li - MnO - NMC

Li -CoO2

Li -CoO2

Anode Material Graphite Hard

CarbonLTO (“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

There are many variations of “Li-Ion” Batteries!

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 cell-by-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 needo When used with Li-Ion type cells, cell balancing & individual cell

OVP must be done externally see bq779xx family devices

Protection and

Balancing not required

for NiXX, PbSO4, etc.

bq34z100Example of typical implementation

bq78PL900bq78PL910Abq77908A

bq34z100Li-Ion Pack Monitor

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

Part 5: Introduction to Wireless Power

Introduction to Battery Management

bqTESLATM Wireless Power Solutions

Wireless Power Consortium (WPC)Interoperability key to adoption

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

Broad Industry Support WPC

and more…

Proprietary Solutions

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)

40% at 1 diameter

1% at 2.5 diameter

0.1% at 4 diameters

0.01% at 6 diameters

Optimal operating distance

Factors Affecting Coupling Efficiency

bq50k + bq51K: Qi-Compliant SolutionPower

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.

(a) No object on pad

(b) RX Device placed on pad

Vertical Scale: 20V/divHorizontal Scale: 20 uS/div

Analog Ping with and without object on pad

Analog Ping / Digital Ping / Startup

Vertical Scale: 20V/divHorizontal Scale: 200 mS/div

TX COIL VOLTAGE

Analog Pings – no object detected

Analog Ping – object detected. Followed by subsequent Digital Ping and initiation of communications functions

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. 80 KHz 100 KHz 120 KHz

Operating Point

bqTesla System Efficiency Breakdown

Measured from DC input of Transmitter to DC output of Receiver

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 520%

30%

40%

50%

60%

70%

80%

90%

100%

Tx Eff. Magnetics Eff. Rx Eff. System Efficiency

Output Power (W)

Eff

icie

ncy

(%

) System Eff

TX EffMagnetics Eff

RX Eff

bqTESLA EVMsbqTESLA Evaluation Modules

bq500210EVM-689

bq51013EVM-725

New

Qi-compliant coil used w/ EVM kit

40-mm x 30-mm x 0.75-mm

WPC Compliant Receiver CoilWPC Compliant Receiver Coil

WPC Compliant Transmitter CoilWPC 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 Powerhttp://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 benefitfrom at a later date.

– One question per-post to make it easer to search.

– Place P/N in Topic with descriptionof 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