TEXAS INSTRUMENTS bq2050H Technical data

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bq2050H

Low-Cost Lithium Ion Power Gauge™ IC

Features

Accurate measurement of avail

➤

able capacity in Lithium Ion bat teries

Provides a low-cost battery man

➤

agement solution for pack integration

Complete circuit can fit in as

little as Low operating current (120µA

square inch of PCB

typical)

Less than 100nA of data

retention current

High-speed (5kb) single-wire

➤

communication interface (HDQ bus) for critical battery parameters

➤ Monitors and controls charge FET

in Li-Ion pack protection circuit

➤ Direct drive of remaining capacity

LEDs

➤ Measurements automatically

compensated for rate and temperature

➤ 16-pin narrow SOIC

General Description

The bq2050H Lithium Ion Power Gauge™ IC is intended for battery-

pack or in-system installation to maintain an accurate record of

available battery capacity. The IC

monitors a voltage drop across a sense resistor connected in series between the negative battery termi nal and ground to determine charge and discharge activity of the battery. Compensations for bat tery temperature, self discharge, and rate of discharge are applied to the charge counter to provide avail able capacity information across a wide range of operating conditions. Battery capacity is automatically re calibrated, or “learned,” in the course of a discharge cycle from full to empty.

Nominal available capacity may be directly indicated using a fivesegment LED display. These seg-

ments are used to graphically indi cate available capacity. The bq2050H also supports a simple single-line bidirectional serial link to an external processor (common ground). The 5kb HDQ bus interface reduces communications overhead in the external microcontroller.

Internal registers include available

capacity, temperature, scaled avail

able energy, battery ID, battery status, and Li-Ion charge FET

status. The external processor may

also overwrite some of the bq2050H power gauge data registers.

The bq2050H can operate from the

batteries in the pack. The REF out

put and an external transistor allow a simple, inexpensive voltage regulator to supply power to the circuit from the cells.

Pin Connections

LCOM

SEG1/PROG

SEG2/PROG

SEG3/PROG

SEG4/PROG

SEG5/PROG

SLUS150–MAY 1999 D

CFC

16-Pin Narrow SOIC

Pin Names

LCOM LED common output

/PROG1LED segment 1/

SEG

REF

PSTAT

HDQ

RBI

DISP

PN2050H1.eps

/PROG2LED segment 2/

SEG

/PROG3LED segment 3/

SEG

/PROG4LED segment 4/

SEG

/PROG5LED segment 5/

SEG

CFC Charge FET control

program 1 input

program 2 input

program 3 input

program 4 input

program 5 input

output

System ground

SR Sense resistor input

DISP

Display control input

SB Battery sense input

RBI Register backup input

HDQ Serial communications

input/output

PSTAT Protector status input

REF Voltage reference output

Supply voltage

bq2050H

Pin Descriptions

LCOM

SEG SEG

PROG PROG

PROG

CFC

LED common output

This open-drain output switches V source current for the LEDs. The switch is off during initialization to allow reading of the soft pull-up or pull-down program resis tors. LCOM is also high impedance when the display is off.

LED display segment outputs (dual func

–

tion with PROG

Each output may activate an LED to sink the current sourced from LCOM.

Programmed full count selection inputs

–

(dual function with SEG

These three-level input pins define the pro grammed full count (PFC) thresholds de scribed in Table 2.

Power gauge scale selection inputs (dual

–

function with SEG

These three-level input pins define the scale factor described in Table 2.

Self-discharge rate selection (dual func-

tion with SEG

This three-level input pin defines the self-discharge and battery compensation factors as shown in Table 1.

Charge FET control output

This pin can be used as an additional control to the charge FET of the Li-Ion pack protec tion circuitry.

Ground

Sense resistor input

The voltage drop (V sistor R time to interpret charge and discharge activ

is monitored and integrated over

ity. The SR input is tied between the nega tive terminal of the battery and the sense re sistor. V V voltage drop, V is V

SR<VSS

SR>VSS

SR+VOS

–PROG5)

–SEG2)

–SEG4)

)

) across the sense re

indicates discharge, and

indicates charge. The effective

, as seen by the bq2050H

SRO

DISP

RBI

HDQ

PSTAT

REF

Display control input

high disables the LED display. DISP

DISP tied to VCCallows PROGXto connect di rectly to V pull-up or pull-down resistor. DISP

or VSSinstead of through a

floating allows the LED display to be active during charge. DISP

low activates the display. See

Table 1.

Secondary battery input

This input monitors the battery cell voltage potential through a high-impedance resis tive divider network for end-of-discharge voltage (EDV) thresholds and battery-removed detection.

This pin is used to provide backup potential to the bq2050H registers during periods when V

3V. A storage capacitor or a battery

≤

can be connected to RBI.

Serial communication input/output

This is the open-drain bidirectional communications port.

Protector status input

This input provides overvoltage status from the Li-Ion protector circuit. It should connect to V

when not used.

Voltage reference output for regulator

REF provides a voltage reference output for an optional micro-regulator.

Supply voltage input

bq2050H

Functional Description

General Operation

The bq2050H determines battery capacity by moni toring the amount of current input to or removed from a rechargeable battery. The bq2050H meas ures discharge and charge currents, measures bat tery voltage, estimates self-discharge, monitors the battery for low battery-voltage thresholds, and com pensates for temperature and discharge rate. Cur rent measurement is measured by monitoring the voltage across a small-value series sense resistor be tween the negative battery terminal and ground. Scaled available energy is estimated using the re maining average battery voltage during the dis charge cycle and the remaining nominal available

bq2050H

Power Gauge IC

LCOM

SEG1/PROG

SEG2/PROG

SEG3/PROG

SEG4/PROG

SEG5/PROG

CFC

PSTAT

REF

DISP

RBI

HDQ

capacity. The scaled available energy measurement is corrected for environmental and operating condi tions.

Figure 1 shows a typical battery pack application of the bq2050H using the LED display capability as a charge-

state indicator. The bq2050H is configured to display

capacity in relative display mode. The relative display

mode uses the last measured discharge capacity of the

battery as the battery “full” reference. A push-button

display feature is available for momentarily enabling

the LED display.

The bq2050H monitors the charge and discharge cur

rents as a voltage across a sense resistor. (See R

ure 1.) A filter between the negative battery terminal

and the SR pin is required.

Q1 ZVNL110A

100K

0.1µF

See note 4

in Fig

Notes:

1. Indicates optional.

2. Programming resistors and ESD-protection diodes are not shown.

3. RC on SR is required.

4. A series diode is required on RBI if the bottom series cell is used as the backup source. If the cell is used, the backup capacitor is not required, and the anode is connected to the positive terminal of the cell.

Figure 1. Battery Pack Application Diagram—LED Display

Charger

Load

FG2050H1.eps

bq2050H

Voltage Thresholds

In conjunction with monitoring VSRfor charge/discharge currents, the bq2050H monitors the battery potential through the SB pin. The voltage is determined through a resistor-divider network per the following equation:

RB1 RB2

4N=−1

where N is the number of cells, RB1 is connected to the positive battery terminal, and RB2 is connected to the negative battery terminal. The single-cell battery volt age is monitored for the end-of-discharge voltage (EDV) thresholds. The EDV threshold levels are used to deter mine when the battery has reached an “empty” state.

The EDV thresholds for the bq2050H are programmable with the default values fixed at:

EDV1 (first) = 0.76V

EDVF (final) = EDV1-0.025V = 0.735V

If V

is below either of the two EDV thresholds, the as

sociated flag is latched and remains latched, independent of V also available over the serial port.

, until the next valid charge. The VSBvalue is

During discharge and charge, the bq2050H monitors V

for various thresholds used to compensate the

charge counter. EDV monitoring is disabled if the discharge rate is greater than 2C (OVLD Flag = 1) and re-

sumes

second after the rate falls below 2C.

RBI Input

The RBI input pin is intended to be used with a storage capacitor or external supply to provide backup potential to the internal bq2050H registers when V

3.0V. V ing an external supply (such as the bottom series cell) as

is output on RBI when VCCis above 3.0V. If us

drops below

the backup source, an external diode is required for isola tion.

Reset

The bq2050H can be reset by removing VCCand ground ing the RBI pin for 15 seconds or by commands over the serial port. The serial port reset command sequence re quires writing 00h to register PPFC (address = 1Eh) and then writing 00h to register LMD (address = 05h).

Temperature

The bq2050H internally determines the temperature in 10°C steps centered from approximately -35°C to +85°C. The temperature steps are used to adapt charge and dis charge rate compensations, self-discharge counting, and available charge display translation. The temperature range is available over the serial port in 10°C incre ments as shown in the following table:

TMP (hex) Temperature Range

0x < -30°C

1x -30°C to -20°C

2x -20°C to -10°C

3x -10°C to 0°C

4x 0°C to 10°C

5x 10°C to 20°C

6x 20°C to 30°C

7x 30°C to 40°C

8x 40°C to 50°C

9x 50°C to 60°C

Ax 60°C to 70°C

Bx 70°C to 80°C

Cx > 80°C

Layout Considerations

The bq2050H measures the voltage differential between the SR and V pin) is greatly affected by PC board layout. For optimal

results, the PC board layout should follow the strict rule

of a single-point ground return. Sharing high-current

ground with small signal ground causes undesirable

noise on the small signal nodes. Additionally:

■

The capacitors (C1 and C2) should be placed as close as possible to the V

respectively, and their paths to V short as possible. A high-quality ceramic capacitor

of 0.1µF is recommended for V

■

The sense-resistor capacitor should be placed as close as possible to the SR pin.

■

The sense resistor (RS) should be as close as possible to the bq2050H.

pins. VOS(the offset voltage at the SR

and SB pins,

should be as

bq2050H

Gas Gauge Operation

The operational overview diagram in Figure 2 illustrates the operation of the bq2050H. The bq2050H accumu lates a measure of charge and discharge currents, as well as an estimation of self-discharge. The accumu lated charge and discharge currents are adjusted for temperature and rate to provide the indication of com pensated available capacity to the host system or user.

The main counter, Nominal Available Capacity (NAC), represents the available battery capacity at any given time. Battery charging increments the NAC register, while battery discharging and self-discharge decrement the NAC register and increment the DCR (Discharge Count Register).

The Discharge Count Register is used to update the Last Measured Discharge (LMD) register only if a complete battery discharge from full to empty occurs without any partial battery charges. Therefore, the bq2050H adapts its capacity determination based on the actual condi tions of discharge.

Inputs

Charge Current

Rate and Temperature Temperature

Compensation Compensation

The battery's initial capacity equals the Programmed Full Count (PFC) shown in Table 2. Until LMD is up dated, NAC counts up to but not beyond this threshold during subsequent charges. This approach allows the

gas gauge to be charger-independent and compatible

with any type of charge regime.

1. Last Measured Discharge (LMD) or learned

battery capacity:

LMD is the last measured discharge capacity of the battery. On initialization (application of V tery replacement), LMD = PFC. During subsequent discharges, the LMD is updated with the latest measured capacity in the Discharge Count Register representing a discharge from full to below EDV1. A qualified discharge is necessary for a capacity transfer from the DCR to the LMD register. The LMD also serves as the 100% reference threshold used by the relative display mode.

Discharge

Current

Self-Discharge

Timer

Temperature

Compensation

or bat

Main Counters

and Capacity

Reference (LMD)

Outputs

Nominal

Available

Charge

(NAC)

Rate and

Temperature

Compensation

Compensated Available Charge LED Display, etc.

Last

Measured

Discharged

(LMD)

Serial

Port

Figure 2. Operational Overview

Discharge

Count

Qualified

Transfer

Temperature Step, Other Data

(DCR)

FG2050H2.eps

bq2050H

2. Programmed Full Count (PFC) or initial bat tery capacity:

The initial LMD and gas gauge rate values are pro grammed by using PROG is configured for a given application by selecting a

–PROG4. The bq2050H

PFC value from Table 2. The correct PFC may be determined by multiplying the rated battery capac ity in mAh by the sense resistor value:

Battery capacity (mAh)*sense resistor (Ω) =

PFC (mVh)

Selecting a PFC slightly less than the rated capac ity provides a conservative capacity reference until

Example: Selecting a PFC Value

Given:

Sense resistor = 0.05

Number of cells = 2 Capacity = 1000mAh, Li-Ion battery, coke-anode

Current range = 50mA to 1A Relative display mode Self-discharge =

NAC

Voltage drop over sense resistor = 2.5mV to 50mV Nominal discharge voltage = 3.6V

Therefore:

1000mAh*0.05Ω= 50mVh

the bq2050H “learns” a new capacity reference.

Table 1. Self-Discharge and Capacity Compensation

Connection

H Coke anode/disabled LEDs disabled

Z Coke anode/

L Graphite anode/

PROG5Compensation/Self-Discharge

(See Tables 3 and 4)

NAC

512

NAC

512

LEDs on when charging

Table 2. bq2050H Programmed Full Count mVh, VSRGain Selections

Ω

per day @ 25°C

512

DISP

Display State

LEDs on for 4 s

Pro-

grammed

PROG

Full

Count

(PFC)

-- -

PROG

SCALE =

1/80

PROG

= L PROG4= Z or H

= H PROG3= Z PROG3= L PROG3= H PROG3= Z PROG3= L

SCALE =

1/160

SCALE =

1/320

SCALE =

1/640

SCALE =

1/1280

SCALE =

1/2560

Units

mVh/ count

H H 49152 614 307 154 76.8 38.4 19.2 mVh

H Z 45056 563 282 141 70.4 35.2 17.6 mVh

H L 40960 512 256 128 64.0 32.0 16.0 mVh

Z H 36864 461 230 115 57.6 28.8 14.4 mVh

Z Z 33792 422 211 106 53.0 26.4 13.2 mVh

Z L 30720 384 192 96.0 48.0 24.0 12.0 mVh

L H 27648 346 173 86.4 43.2 21.6 10.8 mVh

L Z 25600 320 160 80.0 40.0 20.0 10.0 mVh

L L 22528 282 141 70.4 35.2 17.6 8.8 mVh

equivalent to 2

counts/s (nom.)

90 45 22.5 11.25 5.6 2.8 mV

bq2050H

Select:

PFC = 30720 counts or 48mVh

= float

PROG

= low

PROG

= high

PROG

= float

PROG

= float

The initial full battery capacity is 48mVh (960mAh) until the bq2050H “learns” a new capacity with a qualified discharge from full to EDV1.

3. Nominal Available Capacity (NAC):

NAC counts up during charge to a maximum value of LMD and down during discharge and self-dis charge to 0. NAC is reset to 0 on initialization and on the first valid charge following discharge to EDV1. To prevent overstatement of charge during periods of overcharge, NAC stops incrementing when NAC = LMD.

4. Discharge Count Register (DCR):

The DCR counts up during discharge independent of NAC and could continue increasing after NAC has decremented to 0. Prior to NAC = 0 (empty battery), both discharge and self-discharge increment the DCR. After NAC = 0, only discharge increments the DCR. The DCR resets to 0 when NAC = LMD. The DCR does not roll over but stops counting when it reaches FFh.

The DCR value becomes the new LMD value on the first charge after a valid discharge to V the following conditions are met:

■

No valid charge initiations (charges greater than 2 NAC updates where V during the period between NAC = LMD and EDV1.

■

The self-discharge is less than 6% of NAC.

■

The temperature is≥0°C when the EDV1 level

SRO>VSRQ

is reached during discharge.

■

VDQ is set

The valid discharge flag (VDQ) indicates whether the present discharge is valid for LMD update. If the DCR update value is less than 0.94 ∗ LMD, LMD will only be modified by 0.94 ∗ LMD. This prevents invalid DCR values from corrupting LMD.

5. Scaled Available Energy (SAE):

SAE is useful in determining the available energy within the battery, and may provide a more useful capacity reference in battery chemistries with sloped voltage profiles during discharge. SAE may be converted to an mWh value using the following formula:

if all

EDV1

) occurred

E(mWh) =

(SAEH SAEL)∗+ ∗256

12. ∗∗

SCALE (R + R )

B1 B2

SB2

∗

where RB1,RB2, and RSare resistor values in ohms, as shown in Figure 1. SCALE is the selected scale from Table 2.

6. Compensated Available Capacity (CACT)

CACT counts similarly to NAC, but contains the available capacity compensated for discharge rate and temperature.

Charge Counting

Charge activity is detected based on a positive voltage

on the SR input. If charge activity is detected, the bq2050H increments NAC at a rate proportional to V and, if enabled, activates an LED display.

The bq2050H counts charge activity when the voltage at theSRinput(V threshold (V has been updated twice without discharging or reaching

SRQ

) exceeds the minimum charge

SRO

). A valid charge is detected when NAC

the digital magnitude filter time-out. Once a valid charge is detected, charge counting continues until V including offset, falls below V

SRQ

Discharge Counting

Discharge activity is detected based on a negative voltage on the SR input. All discharge counts where V is less than the minimum discharge threshold (V cause the NAC register to decrement and the DCR to increment.

Self-Discharge Counting

The bq2050H continuously decrements NAC and incre ments DCR for self-discharge based on time and tempera ture.

Charge/Discharge Current

The bq2050H current-scale registers, VSRH and VSRL, can be used to determine the battery charge or dis charge current. See the Current Scale Register descrip tion for details.

Count Compensations

Compensated Available Capacity

Compensated Available Capacity compensation is based on the rate of discharge, temperature, and negative electrode type. Tables 3A and 3B outline the correction factor typically used for graphite-anode Li-Ion batteries, and Tables 4A and 4B outline the factors typically used for coke-anode Li-Ion batteries. The compensation factor is applied to NAC to derive the CACD and CACT values.

SRO

SRD

)

bq2050H

Table 3A. Graphite Anode

Approximate Discharge

Rate

0.5C 0

0.5C

≥

Table 3B. Graphite Anode

Temperature

10°C 0

≥

0°C to 10°C

-20°C to 0°C

-20°C

≤

Table 4A. Coke Anode

Approximate Discharge

Rate

0.5C 0

0.5C

≥

Table 4B. Coke Anode

Temperature

10°C 0

≥

0°C to 10°C

-20°C to 0°C

-20°C

≤

Available Capacity

Reduction

0.05 ∗ LMD

Available Capacity

Reduction

0.05 ∗ LMD

0.15 ∗ LMD

0.37 ∗ LMD

Available Capacity

Reduction

0.10 ∗ LMD

Available Capacity

Reduction

0.10 ∗ LMD

0.30 ∗ LMD

0.60 ∗ LMD

Charge Compensation

The bq2050H also monitors temperature during charge. If the temperature is <0°C, NAC will only increment up to 0.94 * LMD, inhibiting VDQ from being set. This keeps a “learn” cycle from occurring when the battery is charged at very low temperatures. If the temperature rises above 0°C, NAC will be allowed to count up to NAC = LMD.

Self-Discharge Compensation

The self-discharge compensation is programmed for a nominal rate of

NAC is reduced for a battery within the 20–30°C tem perature range. This rate varies across 8 ranges from <10°C to >70°C, as shown in Table 5.

∗ NAC per day. This is the rate that

512

Table 5. Self-Discharge Compensation

Typical Rate

Temperature Range

< 10°C

10–20°C

20–30°C

30–40°C

40–50°C

50–60°C

60–70°C

> 70°C

Self-discharge may be disabled by connecting PROG

PROG

= Z or L

NAC

2048

1024

512

256

128

=H.

Digital Magnitude Filter

The bq2050H has a digital filter to eliminate charge and discharge counting below a set threshold. The minimum charge (V

) and discharge (V

SRQ

) threshold for the

SRD

bq2050H is 250µV.

Pack Protection Supervision

The CACD value is the available charge compensated for the rate of discharge. At high discharge rates, CACD is reduced. The reduction is maintained until a valid charge is detected. The CACT value is the available charge compensated for the rate of discharge and tem perature. The CACT value is used to drive the LED dis play.

The bq2050H can monitor the charge FET in a Li-Ion pack protector circuit as shown in Figure 3. If the bat tery voltage is too high or the temperature is out of the 0—60°C range, the bq2050H disables the charge FET with the CFC output, which turns off the charge to the pack.

The PSTAT input is used to monitor the protector state. If PSTAT is above 2.5V, bit 5 of FLGS1 is set to 1. If PSTAT is below 0.5V, bit 5 of FLGS1 is cleared to zero. Using this input, the system can monitor the state of the charge con

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