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bq2010

Gas Gauge IC

Features

Conservative and repeatable

➤

measurement of available charge
in rechargeable batteries

Designed for battery pack inte

➤

gration

120µA typical standby 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

➤ Accurate measurements across a

wide range of current (> 500:1)

➤ 16-pin narrow SOIC

1

2

General Description

The bq2010 Gas Gauge IC is intended
for battery-pack or in-system installa
tion to maintain an accurate record of
a battery's available charge. The IC

­monitors a voltage drop across a

sense resistor connected in series be
tween the negative battery terminal
and ground to determine charge and
discharge activity of the battery.

NiMH and NiCd battery self-dis
charge is estimated based on an inter
nal timer and temperature sensor.
Compensations for battery tempera
ture and rate of charge or discharge
are applied to the charge, discharge,
and self-discharge calculations to pro
vide available charge information
across a wide range of operating con­ditions. Battery capacity is automati­cally recalibrated, or “learned,” in the
course of a discharge cycle from full to
empty.

Nominal available charge may be
directly indicated using a five- or
six-segment LED display. These seg­ments are used to indicate graphi­cally the nominal available charge.

The bq2010 supports a simple
single-line bidirectional serial link to
an external processor (common
ground). The bq2010 outputs battery

­information in response to external
commands over the serial link.

The bq2010 may operate directly

­from 3 or 4 cells. With the REF out

put and an external transistor, a sim
ple, inexpensive regulator can be built
to provide V

-

number of cells.

­Internal registers include available

charge, temperature, capacity, battery

­ID, battery status, and programming

across a greater

CC

pin settings. To support subassembly
testing, the outputs may also be con

­trolled. The external processor may

also overwrite some of the bq2010
gas gauge data registers.

-

-

-

Pin Connections

1

16

2

15

3

14

4

13

5

12

6

11

7

10

8

SEG1/PROG

SEG2/PROG

SEG3/PROG

SEG4/PROG

SEG5/PROG

SEG6/PROG

4/95 D

LCOM

V

1

2

3

4

5

6

SS

16-Pin Narrow SOIC

9

PN201001.eps

V

CC

REF

NC

DQ

EMPTY

SB

DISP

SR

Pin Names

LCOM LED common output

SEG

/PROG1LED segment 1/

1

SEG

/PROG2LED segment 2/

2

SEG

/PROG3LED segment 3/

3

SEG

/PROG4LED segment 4/

4

SEG

/PROG5LED segment 5/

5

SEG

/PROG6LED segment 6/

6

program 1 input

program 2 input

program 3 input

program 4 input

program 5 input

program 6 input

1

REF Voltage reference output

NC No connect

DQ Serial communications

input/output

EMPTY Empty battery indicator

output

SB Battery sense input

DISP

Display control input

SR Sense resistor input

V

CC

V

SS

3.0–6.5V

System ground

bq2010

Pin Descriptions

LCOM

SEG
SEG

PROG
PROG

PROG
PROG

PROG

PROG

NC

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

–

1

tion with PROG

6

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

Programmed full count selection inputs

–

1

(dual function with SEG

2

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

Gas gauge rate selection inputs (dual

–

3

function with SEG

4

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

Self-discharge rate selection (dual func-

5

tion with SEG

This three-level input pin defines the
selfdischarge compensation rate shown in Ta­ble 1.

Display mode selection (dual function

6

with SEG

)

6

This three-level pin defines the display op
eration shown in Table 1.

No connect

–PROG6)

1

)

5

–SEG4)

3

–SEG2)

1

to source

CC

-

-

-

-

-

-

SR

DISP

SB

EMPTY

DQ

REF

V

CC

V

SS

Sense resistor input

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

is monitored and integrated over

S

) across the sense re

SR

ity. The SR input is tied to the high side of
the sense resistor. V
charge, and V
effective voltage drop, V
bq2010 is V

SR+VOS

SR>VSS

SR<VSS

indicates charge. The

(see Table 5).

indicates dis

, as seen by the

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

CC

pull-down resistor. DISP

floating allows the
LED display to be active during discharge or
charge if the NAC registers update at a rate
equivalent to |V
vates the display. See Table 1.

|≥4mV. DISP low acti

SRO

Secondary battery input

This input monitors the single-cell voltage
potential through a high-impedance resis­tive divider network for end-of-discharge
voltage (EDV) thresholds, maximum charge
voltage (MCV), and battery removed.

Battery empty output

This open-drain output becomes high-impedance
on detection of a valid end-of-discharge voltage
(V

) and is low following the next application

EDVF

of a valid charge.

Serial I/O pin

This is an open-drain bidirectional pin.

Voltage reference output for regulator

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

Supply voltage input

Ground

-

-

-

-

2

bq2010

y

Functional Description

General Operation

The bq2010 determines battery capacity by monitoring
the amount of charge input to or removed from a re
chargeable battery. The bq2010 measures discharge and
charge currents, estimates self-discharge, monitors the
battery for low-battery voltage thresholds, and compen
sates for temperature and charge/discharge rates. The
charge measurement derives from monitoring the voltage
across a small-value series sense resistor between the
negative battery terminal and ground. The available bat
tery charge is determined by monitoring this voltage over
time and correcting the measurement for the environ
mental and operating conditions.

bq2010

Gas Gauge IC

LCOM

SEG1/PROG

SEG2/PROG

SEG3/PROG

SEG4/PROG

SEG5/PROG

SEG6/PROG

REF

V

CC

SB

1

2

DISP

3

4

SR

5

V

SS

6

EMPTY

DQ

Figure 1 shows a typical battery pack application of the
bq2010 using the LED display capability as a charge­state indicator. The bq2010 can be configured to display
capacity in either a relative or an absolute display mode.
The relative display mode uses the last measured dis
charge capacity of the battery as the battery “full” refer

-

ence. The absolute display mode uses the programmed
full count (PFC) as the full reference, forcing each seg
ment of the display to represent a fixed amount of

-

charge. A push-button display feature is available for
momentarily enabling the LED display.

The bq2010 monitors the charge and discharge currents
as a voltage across a sense resistor (see R

­A filter between the negative battery terminal and the
SR pin may be required if the rate of change of the bat

-

in Figure 1).

S

tery current is too great.

R

1

Q1
ZVNL110A

C1

µ

0.1 F

V

CC

V

CC

RB

RB

1

2

R

S

-

-

-

-

Indicates optional.

Directly connect to VCC across 3 or 4 cells (3 to 5.6V nominal)

Charger

Load
with a resistor and a Zener diode to limit voltage during charge.
Otherwise, R1, C1, and Q1 are needed for regulation of >4 cells.
The value of R1 depends on the number of cells.

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

R-C on SR ma

be required, application-specific.

FG201001.eps

Figure 1. Battery Pack Application Diagram—LED Display

3

bq2010

Voltage Thresholds

In conjunction with monitoring VSRfor charge/discharge
currents, the bq2010 monitors the single-cell battery
potential through the SB pin. The single-cell voltage
potential is determined through a resistor/divider net
work according to the following equation:

RB

1

N

RB

2

where N is the number of cells, RB
positive battery terminal, and RB
negative battery terminal. The single-cell battery volt

1=−

is connected to the

1

is connected to the

2

age is monitored for the end-of-discharge voltage (EDV)
and for maximum cell voltage (MCV). EDV threshold
levels are used to determine when the battery has
reached an “empty” state, and the MCV threshold is used
for fault detection during charging.

Two EDV thresholds for the bq2010 are fixed at:

V

(early warning) = 1.05V

EDV1

V

(empty) = 0.95V

EDVF

If V

is below either of the two EDV thresholds, the as-

SB

sociated flag is latched and remains latched, indepen­dent of V
monitoring may be disabled under certain conditions as

, until the next valid charge. EDV

SB

described in the next paragraph.

During discharge and charge, the bq2010 monitors V
for various thresholds. These thresholds are used to

SR

compensate the charge and discharge rates. Refer to the
count compensation section for details. EDV monitoring
is disabled if V
after V

> -250mV.

SR

-250mV typical and resumes

≤

SR

1

2

second

EMPTY Output

The EMPTY output switches to high impedance when
V

SB<VEDVF

occurs. The bq2010 also monitors V

2.25V. V

and remains latched until a valid charge

relative to V

falling from above V

SB

SB

resets the device.

MCV

MCV

Reset

The bq2010 recognizes a valid battery whenever VSBis
greater than 0.1V typical. V
or falling from above 2.25V resets the device. Reset can

rising from below 0.25V

SB

also be accomplished with a command over the serial
port as described in the Reset Register section.

Temperature

The bq2010 internally determines the temperature in
10°C steps centered from -35°C to +85°C. The tempera
ture steps are used to adapt charge and discharge rate
compensations, self-discharge counting, and available

charge display translation. The temperature range is
available over the serial port in 10°C increments as
shown below:

-

TMPGG (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 bq2010 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:

n

The capacitors (SB and VCC) should be placed as
close as possible to the SB and V
and their paths to V
A high-quality ceramic capacitor of 0.1µf is
recommended for V

n

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

-

n

The sense resistor (R
possible to the bq2010.

pins. VOS(the offset voltage at the SR

SS

pins, respectively,

should be as short as possible.

SS

.

CC

) should be as close as

SNS

CC

4

Gas Gauge Operation

The operational overview diagram in Figure 2 illustrates
the operation of the bq2010. The bq2010 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 Charge (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
bq2010 adapts its capacity determination based on the
actual conditions of discharge.

The battery's initial capacity is equal to the Programmed
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 allows the gas gauge to
be charger-independent and compatible with any type of
charge regime.

bq2010

Last Measured Discharge (LMD) or learned

1.

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 ca
pacity transfer from the DCR to the LMD register.
The LMD also serves as the 100% reference thresh
old used by the relative display mode.

Programmed Full Count (PFC) or initial bat

2.

tery capacity:

The initial LMD and gas gauge rate values are pro
grammed by using PROG
provides the 100% reference for the absolute dis

–PROG4. The PFC also

1

play mode. The bq2010 is configured for a given ap
plication by selecting a PFC value from Table 2.
The correct PFC may be determined by multiplying
the rated battery capacity in mAh by the sense re
sistor value:

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

PFC (mVh)

Selecting a PFC slightly less than the rated capac­ity for absolute mode provides capacity above the
full reference for much of the battery's life.

CC

or bat

-

-

-

-

-

-

-

-

Inputs

Main Counters

and Capacity

Reference (LMD)

Outputs

Charge
Current

Rate and

Rate and

Temperature

Temperature

Compensation

Compensation

+

Chip-Controlled

Available Charge

Nominal

Available

Charge

(NAC)

Temperature

Translation

LED Display

Discharge

Current

Rate and

Temperature

Compensation

--

<

Discharged

Last

Measured

(LMD)

Serial

Port

Qualified
Transfer

Temperature Step,
Other Data

Figure 2. Operational Overview

5

Self-Discharge

Timer

Temperature

Compensation

+

+

Discharge

Count

Register

(DCR)

FG201002.eps

bq2010

Example: Selecting a PFC Value

Given:

Sense resistor = 0.1

Ω

Number of cells = 6
Capacity = 2200mAh, NiCd battery
Current range = 50mA to 2A
Absolute display mode
Serial port only
Self-discharge =
Voltage drop over sense resistor = 5mV to 200mV

C

64

Therefore:

2200mAh*0.1Ω= 220mVh

Table 1. bq2010 Programming

Pin

Connection

H Disabled

Z

L

Note: PROG5and PROG6states are independent.

PROG

NAC

NAC

5

64

47

Self-Discharge Rate

PROG

Display Mode

Absolute

NAC = PFC on reset

Absolute

NAC = 0 on reset

Relative

NAC = 0 on reset

Table 2. bq2010 Programmed Full Count mVh Selections

Select:

PFC = 33792 counts or 211mVh
PROG

= float

1

PROG

= float

2

PROG

= float

3

PROG

= low

4

PROG

= float

5

PROG

= float

6

The initial full battery capacity is 211mVh
(2110mAh) until the bq2010 “learns” a new capac
ity with a qualified discharge from full to EDV1.

6

DISP

Display State

LED disabled

LED-enabled on discharge or charge

when equivalent |V

SRO

|≥4mV

LED on

-

Pro-

grammed

PROG

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

-- -

Full

x

Count

(PFC)

Scale =

1/80

PROG

= L PROG4= Z

4

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

VSR equivalent to 2

counts/sec. (nom.)

90 45 22.5 11.25 5.6 2.8 mV

6