TEXAS INSTRUMENTS bq2050 Technical data

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Features

Conservative and repeatable

➤

measurement of available capac ity in Lithium Ion rechargeable batteries

Designed for battery pack inte

➤

gration

120µA typical operating

current

Small size enables imple-

mentations in as little as square inch of PCB

Integrate within a system or as a

➤

stand-alone device

Display capacity via single-

wire serial communication port or direct drive of LEDs

➤ Measurements compensated for

current and temperature

➤ Self-discharge compensation us-

ing internal temperature sensor

➤ 16-pin narrow SOIC

bq2050

Lithium Ion Power Gauge™ IC

General Description

The bq2050 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 and rate of charge or discharge are applied to the

charge, discharge, and self-discharge calculations to provide available ca pacity information across a wide range of operating conditions. Bat tery capacity is automatically recali brated, or “learned,” in the course of a discharge cycle from full to empty.

supports a simple single-line bidi rectional serial link to an external processor (common ground). The bq2050 outputs battery information in response to external commands over the serial link.

The bq2050 may operate directly from one cell (V REF output and an external transis

tor, a simple, inexpensive regulator

> 3V). With the

BAT

can be built for systems with more than one series cell.

Internal registers include available

capacity, temperature, scaled avail able energy, battery ID, battery

status, and programming pin set

tings. To support subassembly test

ing, the outputs may also be con

trolled. The external processor may

also overwrite some of the bq2050 power gauge data registers.

Nominal available capacity may be directly indicated using a fivesegment LED display. These segments are used to graphically indicate available capacity. The bq2050

Pin Connections Pin Names

LCOM LED common output

SEG

/PROG1LED segment 1/

/PROG2LED segment 2/

SEG

/PROG3LED segment 3/

SEG

/PROG4LED segment 4/

SEG

/PROG5LED segment 5/

SEG

PROG

9/96 C

LCOM

SEG1/PROG

SEG2/PROG

SEG3/PROG

SEG4/PROG

SEG5/PROG

PROG

16-Pin Narrow SOIC

PN205001.eps

REF

N/C

RBI

DISP

program 1 input

program 2 input

program 3 input

program 4 input

program 5 input

Program 6 input

REF Voltage reference output

N/C No connect

DQ Serial communications

input/output

RBI Register backup input

SB Battery sense input

DISP

Display control input

SR Sense resistor input

3.0–6.5V

System ground

bq2050

Pin Descriptions

LCOM

SEG SEG

PROG PROG

PROG

N/C

LED common output

Open-drain output switches V current for the LEDs. The switch is off dur ing initialization to allow reading of the soft pull-up or pull-down program resistors. LCOM is also high impedance when the dis play 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 rate 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 selfdischarge and battery compensation factors as shown in Table 1.

Capacity initialization selection

This three-level pin defines the battery state of charge at reset as shown in Table 1.

No connect

–PROG6)

)

–SEG4)

–SEG2)

to source

DISP

Sense resistor input

The voltage drop (V sistor R

is monitored and integrated over

) across the sense re

time to interpret charge and discharge activ ity. The SR input is tied between the nega tive terminal of the battery and the sense re sistor. V

SR<VSS

indicates discharge, and V >VSSindicates charge. The effective voltage drop, V V

, as seen by the bq2050 is VSR+

SRO

Display control input

high disables the LED display. DISP

DISP

tied to VCCallows PROGXto connect directly to V

or VSSinstead of through a pull-up or

pull-down resistor. DISP

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 resistive divider network for end-of-discharge voltage (EDV) thresholds, and battery removed.

RBI

This pin is used to provide backup potential to the bq2050 registers during periods when V

≤ 3V. A storage capacitor or a battery

can be connected to RBI.

Serial I/O pin

This is an open-drain bidirectional pin.

REF

Voltage reference output for regulator

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

Supply voltage input

Ground

bq2050

Functional Description

General Operation

The bq2050 determines battery capacity by monitor ing the amount of current input to or removed from a rechargeable battery. The bq2050 measures dis charge and charge currents, measures battery volt age, estimates self-discharge, monitors the battery for low battery voltage thresholds, and compensates for temperature and charge/discharge rates. The cur rent measurement is made by monitoring the voltage across a small-value series sense resistor between the negative battery terminal and ground. The estimate of scaled available energy is made using the remaining average battery voltage during the discharge cycle and the remaining nominal available charge. The

bq2050

Power Gauge IC

LCOM

SEG1/PROG

SEG2/PROG

SEG3/PROG

SEG4/PROG

SEG5/PROG

PROG

PSTAT

REF

DISP

RBI

scaled available energy measurement is corrected for the environmental and operating conditions.

Figure 1 shows a typical battery pack application of the bq2050 using the LED display capability as a chargestate indicator. The bq2050 is configured to display ca

pacity 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 bq2050 monitors the charge and discharge currents

as a voltage across a sense resistor (see R

in Figure 1).

A filter between the negative battery terminal and the SR pin may be required if the rate of change of the bat tery current is too great.

Q1 ZVNL110A

0.1 F V

Indicates optional.

Directly connect to VCC across 1 cell (V

Otherwise, R1, C1, and Q1 are needed for regulation of > 1 cell.

Programming resistors (6 max.) and ESD-protection diodes are not shown.

R-C on SR may be required, application-specific.

A series Zener may be used to limit discharge current at low voltages

ns using 3 or more cells.

in desi

BAT

> 3V).

Charger

Load

FG205001.eps

Figure 1. Battery Pack Application Diagram—LED Display

bq2050

Voltage Thresholds

In conjunction with monitoring VSRfor charge/discharge currents, the bq2050 monitors the battery potential through the SB pin. The voltage is determined through a resistor-divider network per the following equation:

RB1 RB2

2N=−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). EDV threshold levels are used to determine when the battery has reached an “empty” state.

Two EDV thresholds for the bq2050 are programmable with the default values fixed at:

EDV1 (early warning) = 1.52V

EDVF (empty) = 1.47V

If V

is below either of the two EDV thresholds, the as

sociated flag is latched and remains latched, independent of V

, until the next valid charge. The VSBvalue is

also available over the serial port.

During discharge and charge, the bq2050 monitors V

for various thresholds used to compensate the charge and discharge rates. Refer to the count compensation section for details. EDV monitoring is disabled if the discharge rate is greater than 2C (typical) and resumes

second after the rate falls below 2C.

RBI Input

The RBI input pin is intended to be used with a storage ca pacitor or external supply to provide backup potential to the internal bq2050 registers when V

drops below 3.0V. V

is output on RBI when VCCis above 3.0V. A diode is re quired to isolate the external supply.

Reset

The bq2050 can be reset either by removing VCCand grounding the RBI pin for 15 seconds or by writing 0x80 to register 0x39.

Temperature

The bq2050 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 bq2050 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 bq2050.

pins. VOS(the offset voltage at the SR

and SB pins,

should be as

bq2050

Gas Gauge Operation

The operational overview diagram in Figure 2 illustrates the operation of the bq2050. The bq2050 accumulates a measure of charge and discharge currents, as well as an estimation of self-discharge. Charge and discharge cur rents are temperature and rate compensated, whereas self-discharge is only temperature compensated.

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 (DCR) 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 bq2050 adapts its capacity determination based on the actual conditions of discharge.

Inputs

Charge Current

Rate and

Temperature

Compensation

The battery's initial capacity is equal to the Pro grammed Full Count (PFC) shown in Table 2. Until LMD is updated, NAC counts up to but not beyond this threshold during subsequent charges. This approach al lows the gas gauge to be charger-independent and com patible 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 (DCR) representing a discharge from full to below EDV1. A qualified discharge is necessary for a capac ity 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

Rate and

Temperature

Compensation

Self-Discharge

Timer

Temperature

Compensation

or bat

Main Counters

and Capacity

Reference (LMD)

Outputs

Nominal

Available

Charge

(NAC)

Temperature

Translation

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)

FG205002.eps

bq2050

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

The initial LMD and gas gauge rate values are pro grammed by using PROG

–PROG4. The bq2050 is

configured for a given application by selecting a 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 the bq2050 “learns” a new capacity reference.

Example: Selecting a PFC Value

Given:

Sense resistor = 0.05

Ω

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

Current range = 50mA to 1A Relative display mode Serial port only Self-discharge = Voltage drop over sense resistor = 2.5mV to 50mV

NAC

per day @ 25°C

512

Nominal discharge voltage = 3.6V

Therefore:

1000mAh*0.05Ω= 50mVh

Table 1. bq2050 Programming

Connection

H Table 4/Disabled PFC LEDs disabled

Z Table 4/

L Table 3/

Note: PROG5and PROG6states are independent.

PROG5Compensation/

Self-Discharge

NAC

512

NAC

512

PROG

NAC on Reset

Display State

0 LEDs on when charging

0 LEDs on for 4 sec.

DISP

Table 2. bq2050 Programmed Full Count mVh Selections

Pro-

grammed

PROG

Full

Count

1 2 PROG3 = H PROG3 = Z PROG3 = L PROG3 = H PROG3 = Z PROG3 = L

-- -

(PFC)

SCALE =

1/80

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

VSR equivalent to 2

counts/sec. (nom.)

90 45 22.5 11.25 5.6 2.8 mV

PROG

= L PROG4= Z

SCALE =

1/160

SCALE =

1/320

SCALE =

1/640

SCALE =

1/1280

SCALE =

1/2560

Units

mVh/ count

bq2050

Select:

PFC = 30720 counts or 48mVh

= float

PROG

= low

PROG

= high

PROG

= float

PROG

= float

PROG

= float

The initial full battery capacity is 48mVh (960mAh) until the bq2050 “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 FFFFh.

The DCR value becomes the new LMD value on the first charge after a valid discharge to V

EDV1

No valid charge initiations (charges greater than 256 NAC counts, where V

SRO>VSRQ

) occurred dur ing the period between NAC = LMD and EDV1 de tected.

The self-discharge count is not more than 4096 counts (8% to 18% of PFC, specific percentage threshold determined by PFC).

The temperature is≥0°C when the EDV1 level is reached during discharge.

The valid discharge flag (VDQ) indicates whether the present discharge is valid for LMD update.

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 a mWh value using the following formula:

E(mWh) =

(* *SAEH SAEL)256 +

24.)∗∗+

SCALE (R R

B1 B2

∗

SB2

where RB1,RB2and RSare resistor values in ohms. SCALE is the selected scale from Table 2. SAEH and SAEL are digital values read via DQ.

6. Compensated Available Capacity (CAC)

CAC counts similar to NAC, but contains the avail

able capacity compensated for discharge rate and temperature.

Charge Counting

Charge activity is detected based on a positive voltage on the V bq2050 increments NAC at a rate proportional to V if enabled, activates an LED display. Charge actions in

input. If charge activity is detected, the

and,

crement the NAC after compensation for temperature.

The bq2050 determines charge activity sustained at a continuous rate equivalent to V

SRO>VSRQ

. A valid charge equates to sustained charge activity greater than 256 NAC counts. Once a valid charge is detected, charge counting continues until V below V

SRQ

is 210µV, and is described in the

SRQ

SRO(VSR+VOS

) falls

Digital Magnitude Filter section.

Discharge Counting

Discharge activity is detected based on a negative voltage on the V

if:

cause the NAC register to decrement and the DCR to increment. V

input. All discharge counts where V

is -200µV, and is described in the

SRD

SRO<VSRD

Digital Magnitude Filter section.

Self-Discharge Estimation

The bq2050 continuously decrements NAC and increments DCR for self-discharge based on time and temperature. The self-discharge count rate is programmed to be a nominal

NAC per day or disabled. This is the rate for a bat

512

tery whose temperature is between 20°–30°C. The NAC

Count Compensations

Discharge Compensation

Corrections for the rate of discharge, temperature, and anode type are made by adjusting an internal compensation factor. This factor is based on the measured rate of discharge of the battery. Tables 3A and 3B outline the correction factor typi cally 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 CAC and is based on discharge rate and temperature.

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TEXAS INSTRUMENTS bq2050 Technical data

Specifications and Main Features

Frequently Asked Questions

User Manual