Texas Instruments BQ2052SN-A515TR, BQ2052SN-A515 Datasheet

Features

➤

Accurate measurement of avail

able capacity in Lithium primary batteries such as Lithium Sul

phur Dioxide and Lithium Man

ganese Dioxide

➤

Provides a low-cost battery moni

tor solution for pack integration

Complete circuit can fit less than 1 square inch of PCB space

Low operating current

Less than 100nA of data retention current

➤ Single-wire communication inter-

face (HDQ bus) for critical battery parameters

➤ Communicates remaining capac-

ity with direct drive of LEDs in 3 selectable modes

➤ Measurements automatically

compensated for discharge rate and temperature

➤ 16-pin narrow SOIC

General Description

The bq2052 Lithium Primary Gas Gauge IC is intended for bat

tery-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 with the cells to determine dis

charge activity of the battery. The bq2052 applies compensations for battery temperature and discharge rate to the available charge counter to provide available capacity infor

mation across a wide range of oper

ating conditions.

Compensated available capacity may be directly indicated using an LED display. The LED display is programmable and can be configured as two, four, or five segments. These segments are used to depict available battery capacity. The bq2052 supports a single-wire serial

communications link to an external micro-controller. The link allows the micro-controller to read and write the internal registers of the bq2052. The internal registers in

clude available battery capacity, voltage, temperature, current, and battery status. The controller may also overwrite some of the bq2052 gas gauge data registers.

The bq2052 can operate from the batteries in the pack. The REF out

put and an external FET provide a simple, inexpensive voltage regula

tor to supply power to the circuit from the cells.

Preliminary

bq2052

LCOM LED common output

SEG

/PROG1LED segment 1/

program 1 input

SEG

/PROG2LED segment 2/

program 2 input

SEG

/PROG3LED segment 3/

program 3 input

SEG

/PROG4LED segment 4/

program 4 input

SEG

/PROG5LED segment 5/

program 5 input

CP Control port

PN2052H1.eps

16-Pin Narrow SOIC

REF

PROG

HDQ

RBI

DISP

LCOM

SEG1/PROG

SEG2/PROG

SEG3/PROG

SEG4/PROG

SEG5/PROG

Pin Connections

SLUS019–MAY 1999

Gas Gauge IC

for Lithium Primary Cells

Pin Names

System ground

SR Sense resistor input

DISP

Display control input

SB Battery sense input

RBI Register backup input

HDQ Serial communications

input/output

PROG

Program 6 input

REF Voltage reference output

Supply voltage

Pin Descriptions

LCOM

LED common output

This open-drain output switches V

to 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.

SEG

–

SEG

LED display segment outputs (dual func

tion with PROG

–PROG5)

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

PROG

–

PROG

Programmed full count selections

These three-level input pins define the pro

grammed full count.

PROG

Power gauge scale selection inputs (dual function with SEG

–SEG4)

This three-level input pin defines the scale factor.

PROG

Programmed compensation factors

This three-level input pin defines the battery discharge compensation factors.

PROG

Programmed display mode

This three-level input pin defines the capac

ity indication display mode.

PROG

Programmed initial capacity state

This input defines the initial battery capac

ity indication state. When tied to V

, the bq2052 sets the available capacity to full on reset. When tied to V

, the bq2052 sets the

available capacity to zero on reset.

Ground

Sense resistor input

The voltage drop (V

) across the sense resis

tor R

is monitored and integrated over time

to interpret discharge activity. V

SR>VSS

dicates discharge. The effective voltage drop, V

SRO

, as seen by the bq2052 is VSR+VOS.

DISP

Display control input

DISP

high disables the LED display. DISP tied to VCC(no display LEDs in the circuit) allows PROG

to connect directly to VCCor

instead of through a pull-up or

pull-down resistor. DISP

low activates the

display.

Secondary battery input

This input monitors the battery cell voltage potential through a high-impedance resis

tive divider network for the end-of-discharge voltage (EDV) thresholds.

RBI

This pin is used to provide backup potential to the bq2052 registers during periods when V

≤

3V. A storage capacitor or a battery can be

connected to RBI.

HDQ

Serial communication input/output

This is the open-drain bidirectional communications port.

Control port

This open drain output may be controlled by serial port commands and its state is re

flected in the CPIN bit in FLGS1.

REF

Voltage reference output for regulator

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

Supply voltage input

bq2052

Preliminary

Functional Description

General Operation

The bq2052 determines battery capacity by monitoring the amount of charge removed from a primary battery. The bq2052 measures discharge currents and battery voltage, monitors the battery for the low battery-voltage thresholds, and compensates available capacity for tem

perature and discharge rate. The bq2052 measures ca

pacity by monitoring the voltage across a small-value se

ries sense resistor between the negative battery termi

nal and ground.

Figure 1 shows a typical battery pack application of the bq2052 using the LED display capability as a charge-state indicator. The bq2052 displays capacity with two, four, or five LEDs using the programmed full count (PFC) as the battery’s “full” reference. The bq2052 has a push-button input for momentarily enabling the LED display.

Measurements

The bq2052 uses a voltage-to-frequency converter (VFC) for discharge measurement and an analog-to-digital con

verter (ADC) for battery voltage measurement.

Discharge Counting

The VFC measures the discharge flow of the battery by monitoring a small value sense resistor between the SR pin and V

as shown in Figure 1. The bq2052 detects “discharge” activity when the potential at the SR input, V

SRO

, is positive. The bq2052 integrates the signal over

time using an internal counter. The fundamental rate of the counter is 3.125µVh. The VFC measures signals up to 0.5V in magnitude.

Digital Magnitude Filter

The bq2052 has a digital filter to eliminate discharge counting below a set threshold. The minimum discharge threshold, V

SRD

, for the bq2052 is 250µV.

Preliminary

bq2052

FG205201.eps

PROG6

HDQ

SEG

DISP

REF

bq2052

Gas Gauge IC

LCOM

RBI

0.1µF

Q1 ZVNL110A

100K

Load

Indicates optional.

2. VCC can connect directly to two lithium primary cells (6.0V nominal and should not exceed 6.5V). Otherwise, R1, C1, and Q1 are needed for regulation of > 2 cells.

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

4. R-C on SR is required.

To µC

H or L

5. 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.

Notes:

Figure 1. Application Diagram—5-Segment LED Display

Voltage Monitoring and Thresholds

In conjunction with monitoring the SR input for dis

charge currents, the bq2052 monitors the battery poten

tial through the SB pin. The voltage at the SB pin, V

, is developed through a high impedance resistor network connect across the battery. The bq2052 monitors the voltage at the SB pin and reports the voltage in the VSB register (address = 0bh).

The bq2052 compares the V

reading to two end-of-discharge voltage (EDV) thresholds. The EDV threshold levels are used to determine when the battery has reached an “empty” state. The EDV thresholds for the bq2052 are programmable with the default values fixed at:

EDV1 (first) = 0.76V

EDVF (final) = EDV1 - 0.10V = 0.66V

If V

is below either of the two EDV thresholds for 8 consecutive samples over a 4 second period, the bq2052 sets the associated flag in the FLGS1 register (address = 01h). Once set, the EDV flags remain set, independent of V

Temperature

The bq2052 has an internal temperature sensor to mea

sure temperature. The bq2052 determines the tempera

ture and stores it in the TEMP register (address = 02h). The bq2052 uses temperature to adapt remaining capac

ity for the battery’s discharge efficiency.

Gas Gauge Operation

General

The operational overview diagram in Figure 2 illustrates the operation of the bq2052. The bq2052 accumulates a measure of discharge currents and calculates available capacity. The bq2052 compensates available capacity for discharge rate and temperature and provides the information in the Compensated Available Capacity (CAC) registers (address = 0eh–0fh). The main counter, Discharge Count Register (DCR) (address = 2eh), represents the cumulative amount of charge removed from the battery. Battery discharging increments the DCR register.

bq2052

Preliminary

FG2052.eps

Efficiency

Factor

Discharge

Current

Rate and

Temperature

Compensated

Available Capacity

(CAC)

Complete

Data Set

Full Nominal

Available Charge

(FNAC)

Discharge

Count

(DCR)

Inputs

Main Counters

Outputs

Chip-Controlled

Available Charge

LED Display

Serial Port

–

Figure 2. Operational Overview

Symbol Parameter Typical Maximum Units Notes

INL

Integrated non-linearity error

Add 0.1% per °C above or below 25°C and 1% per volt above or below 4.25V.

INR

Integrated nonrepeatability error

Measurement repeatability given similar operating conditions.

Table 1. bq2052 Current-Sensing Errors

Main Gas-Gauge Registers

Programmed Full Count

The PFC register stores the user-specified battery full capacity. The 8-bit PFC registers stores the full capacity in mVh scaled as shown in Table 2.

Full Nominal Available Capacity

The FNAC register stores the full capacity reference of the battery. It can be programmed to initialize to PFC or zero. The 8-bit FNAC register stores data scaled to the same units as PFC. The bq2052 does not update FNAC during the course of operation; therefore, if it is programmed to 0 on initialization, it must be written to full using the serial port.

Discharge Count Register

The DCR is the main gas gauging register and contains the cumulative amount of discharge counted by the bq2052. The 16-bit register stores data scaled to the same units as PFC.

Compensated Available Capacity

The CAC registers contain the current available capac

ity of the battery. The data stored in CAC represents the amount of remaining capacity of the battery compen

sated for rate and temperature use conditions. Tables 3, 4, and, 5 outline the options for typical efficiency com

pensation factors for lithium primary batteries. The bq2052 applies the efficiency factors to FNAC to derive CAC.

The bq2052 applies the compensation according to the formula:

CAC = [F

∗ FNAC] - DCR

Where F

is the calculated efficiency compensation factor, FNAC = Full Nominal Available Capacity and DCR = Discharge Count Register.

The bq2052 calculates an F

based on the battery discharge rate and temperature. The discharge rate portion of the F

compensation is a “peak hold” function; therefore, the bq2052 latches the highest discharge rate it has measured and uses the highest rate to calculate F

throughout the complete discharge cycle. The highest discharge rate measured by the bq2052 is stored in MRATE (address = 12h).

The bq2052 does not latch the temperature portion of an F

calculation. Therefore, CAC may increase or de

crease during the course of a complete discharge cycle if a temperature shift causes a change in the calculated F

value.

Programming the bq2052

The bq2052 is programmed with the PROG

1–6

pins. During power-up or initialization, the bq2052 reads the state of these six three-level inputs and latches in the programmable configuration settings.

Preliminary

bq2052

PROG

Programmed

Full Count

(PFC)

PROG

Units12 H Z L

-- -

SCALE =

1/40

SCALE =

1/80

SCALE =

1/160

mVh/ count

H H 48128 1203 602 301 mVh

H Z 46080 1152 576 288 mVh

H L 43264 1082 541 271 mVh

Z H 39936 998 499 250 mVh

Z Z 38400 960 480 240 mVh

Z L 36096 902 451 226 mVh

L H 31744 794 397 199 mVh

L Z 28928 723 362 181 mVh

L L 26112 653 327 164 mVh

Table 2. bq2052 Programmed Full Count mVh

Programmable Configuration Settings

Design Capacity

The battery’s rated design capacity or Programmed Full Count (PFC) is programmed with the PROG

–PROG

pins as shown in Table 2, and represents the battery’s full reference.

The correct PFC may be determined by multiplying the rated battery capacity in mAh by the sense resistor value:

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

Selecting a PFC slightly less than the rated capacity provides a conservative capacity reference. The bq2052 stores the selected PFC in the PFC register (address = 10h).

Discharge Rate and Temperature Compensation

The discharge rate and temperature compensations are se

lected using the PROG

pin. The level of PROG4on power-up or initialization determines which compensation table the bq2052 uses for the discharge cycle. The following tables illustrate the calculated efficiency compensation factors at selected discharge rates and temperatures.

Table 3. Discharge Efficiency Factor Table

PROG4 = Z

TEMP

Discharge Rage

0 C/80 C/25 C/10 C/5 C/3

-20 97 99 96 92 85 81

-10 98 98 97 94 89 85 0 989897949087

21 99 99 98 96 92 89 55 99 99 98 96 93 90 70 99 99 98 96 93 90

Table 4. Discharge Efficiency Factor Table

PROG4 = L

TEMP

Discharge Rage

0 C/80 C/25 C/10 C/5 C/3

-20 87 85 80 70 53 50

-10 93 91 88 80 68 51 0 969491857460

21 99 97 95 89 81 68 55 100 99 97 92 85 74 70 101 100 98 93 86 76

Table 5. Discharge Efficiency Factor Table

PROG4 = H

TEMP

Discharge Rage

0 C/80 C/25 C/10 C/5 C/3

-20 92 93 92 88 83 75

-10 98 98 97 93 89 81 0 100 100 99 96 91 84

21 104 104 102 99 95 88 55 106 106 105 100 97 90 70 107 107 105 101 98 91

Display Mode

The display mode is selected using the PROG5pin. The three options include a two, four, or five segment display mode as described in Tables 7, 8, and 9.

Initial Capacity Setting

The PFC value is copied to the FNAC register if PROG

is programmed high, otherwise FNAC defaults to 0. FNAC may be written to the desired full capacity to initialize the pack manually.

Programming Example

Given:

Sense resistor = 0.05mΩ Number of cells=5inseries Capacity = 7000mAh, Chemistry = LiSO

Discharge current range = 250mA to 2A Voltage drop over sense resistor = 12.5mV to 100mV Display mode = 5 segment bar graph display

Therefore:

7000mAh*0.05 = 350mVh

Select:

PFC = 26112 counts or 327mVh PROG

= low

PROG

= low

PROG

= float

PROG

= float, high, or low depending on desired com

pensation factors PROG

= float selects five segment display

PROG

= high sets FNAC to PFC

With these selections, the full battery capacity is 327mVh (6540mAh).

bq2052

Preliminary

+ 12 hidden pages