Texas Instruments EV2012, BQ2012SN-D107TR, BQ2012SN-D107 Datasheet

1

Features

➤

Conservative and repeatable
measurement of available charge
in rechargeable batteries

➤

Charge control output

➤

Designed for battery pack inte

-

gration

-

120µA typical standby current
(self-discharge estimation mode)

-

Small size enables imple­mentations in as little as

1

2

square inch of PCB

➤ Integrate within a system or as a

stand-alone device

-

Display capacity via single­wire 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

General Description

The bq2012 Gas Gauge IC is in

­tended for battery-pack or in-system
installation to maintain an accurate
record of available battery charge.
The IC monitors a voltage drop
across a sense resistor connected in
series between the negative battery
terminal and ground to determine
charge and discharge activity of the
battery.

Self-discharge of NiMH and NiCd
batteries is estimated based on an
internal timer and temperature sen

­sor. Compensations for battery tem

­perature and rate of charge or dis­charge are applied to the charge,
discharge, and self-discharge calcu­lations to provide 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.

The bq2012 includes a charge con­trol output that, when used with
other full-charge safety termination
methods, can provide a cost-effective

means of controlling charge based
on the battery's charge state.

Nominal available charge may be di

­rectly indicated using a five- or six­segment LED display. These seg

­ments are used to graphically indi

­cate nominal available charge.

The bq2012 supports a simple
single-line bidirectional serial link to
an external processor (common
ground). The bq2012 outputs battery
information in response to external
commands over the serial link.

Internal registers include available
charge, temperature, capacity, battery
ID, battery status, and programming
pin settings. To support subassembly
testing, the outputs may also be con­trolled. The external processor may
also overwrite some of the bq2012 gas
gauge data registers.

The bq2012 may operate directly
from three or four cells. With the
REF output and an external transis­tor, a simple, inexpensive regulator
can be built to provide V

CC

across a

greater number of cells.

LCOM LED common output

SEG

1

/PROG1LED segment 1/

program 1 input

SEG

2

/PROG2LED segment 2/

program 2 input

SEG

3

/PROG3LED segment 3/

program 3 input

SEG

4

/PROG4LED segment 4/

program 4 input

SEG

5

/PROG5LED segment 5/

program 5 input

SEG

6

/PROG6LED segment 6/

program 6 input

1

PN201201.eps

16-Pin Narrow SOIC

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

LCOM

SEG1/PROG

1

SEG2/PROG

2

SEG3/PROG

3

SEG4/PROG

4

SEG5/PROG

5

SEG6/PROG

6

V

SS

V

CC

REF

CHG

DQ

EMPTY

SB

DISP

SR

REF Voltage reference output

CHG

Charge control output

DQ Serial communications

input/output

EMPTY Empty battery indicator

output

SB Battery sense input

DISP

Display control input

SR Sense resistor input

V

CC

3.0–6.5V

V

SS

System ground

Pin Connections Pin Names

bq2012

Gas Gauge IC With

Slow-Charge Control

9/96 B

Pin Descriptions

LCOM

LED common output

Open-drain output switches V

CC

to source

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.

SEG

1

–

SEG

6

LED display segment outputs (dual func

­tion with PROG

1

–PROG6)

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

PROG

1

–

PROG

2

Programmed full count selection inputs
(dual function with SEG

1

–SEG2)

These three-level input pins define the pro

­grammed full count (PFC) thresholds de

­scribed in Table 2.

PROG

3

–

PROG

4

Gas gauge rate selection inputs (dual
function with SEG

3

–SEG4)

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

PROG

5

Self-discharge rate selection (dual func­tion with SEG

5

)

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

PROG

6

Display mode selection (dual function
with SEG

6

)

This three-level pin defines the display op

­eration shown in Table 1.

CHG

Charge control output

This open-drain output becomes active low
when charging is allowed. Valid charging
conditions are described in the Charge Con

­trol section.

SR

Sense resistor input

The voltage drop (V

SR

) across the sense re

-

sistor R

S

is monitored and integrated over

time to interpret charge and discharge activ

­ity. The SR input is tied to the high side of
the sense resistor. V

SR<VSS

indicates dis

­charge, and V

SR>VSS

indicates charge. The

effective voltage drop (V

SRO

) as seen by the

bq2012 is V

SR+VOS

(see Table 5).

DISP

Display control input

DISP

high disables the LED display. DISP
tied to VCCallows PROGXto connect directly
to V

CC

or VSSinstead of through a pull-up or

pull-down resistor. DISP

floating allows the
LED display to be active during a valid
charge or during discharge if the NAC regis

-

ter is updated at a rate equivalent to V

SRO

≤

-4mV. DISP

low activates the display. See

Table 1.

SB

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.

EMPTY

Battery empty output

This open-drain output becomes high­impedance on detection of a valid end-of­discharge voltage (V

EDVF

) and is low following

the next application of a valid charge.

DQ

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.

V

CC

Supply voltage input

V

SS

Ground

2

bq2012

Functional Description

General Operation

The bq2012 determines battery capacity by monitoring
the amount of charge input to or removed from a re

­chargeable battery. The bq2012 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 is made by monitoring the voltage
across a small-value series sense resistor between the
negative battery terminal and ground. The available
battery charge is determined by monitoring this voltage
over time and correcting the measurement for the envi

­ronmental and operating conditions.

Figure 1 shows a typical battery pack application of the
bq2012 using the LED display capability as a charge­state indicator. The bq2012 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 bq2012 monitors the charge and discharge currents
as a voltage across a sense resistor (see R

S

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.

3

bq2012

FG201201.eps

SEG6/PROG

6

SEG5/PROG

5

SEG4/PROG

4

SEG3/PROG

3

SEG2/PROG

2

SEG1/PROG

1

SR

DISP

SB

V

CC

REF

bq2012

Gas Gauge IC

LCOM

V

SS

EMPTY

DQ

V

CC

C1

0.1 F

Q1
ZVNL110A

R

1

R

S

RB

1

RB

2

Load

Charger

Indicates optional.

Directly connect to VCC across 3 or 4 cells (3 to 4.8V nominal,should not
exceed 6.5V) 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 may be required (application-specific), where the R
should not exceed 100k.

V

CC

CHG

1M

Figure 1. Battery Pack Application Diagram—LED Display

Voltage Thresholds

In conjunction with monitoring VSRfor charge/discharge
currents, the bq2012 monitors the single-cell battery po

-

tential through the SB pin. The single-cell voltage po

­tential is determined through a resistor/divider network
per the following equation:

RB
RB

N

1

2

1=−

where N is the number of cells, RB

1

is connected to the

positive battery terminal, and RB

2

is connected to the

negative battery terminal. The single-cell battery volt

­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 bq2012 are fixed at:

EDV1 (early warning) = 1.05V

EDVF (empty) = 0.95V

If V

SB

is below either of the two EDV thresholds, the as­sociated flag is latched and remains latched, independ­ent of V

SB

, until the next valid charge.

During discharge and charge, the bq2012 monitors V

SR

for various thresholds. These thresholds are used to
compensate the charge and discharge rates. Refer to the
count compensation section for details. EDV monitoring
is disabled if V

SR

≤

-250mV typical and resumes

1

2

sec-

ond after V

SR

> -250mV.

EMPTY Output

The EMPTY output switches to high impedance when
V

SB<VEDF

and remains latched until a valid charge oc

-

curs. The bq2012 also monitors V

SB

relative to V

MCV

,

2.25V. V

SB

falling from above V

MCV

resets the device.

Reset

The bq2012 recognizes a valid battery whenever VSBis
greater than 0.1V typical. V

SB

rising from below 0.25V
or falling from above 2.25V resets the device. Reset can
also be accomplished with a command over the serial
port as described in the Register Reset section.

Temperature

The bq2012 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:

Layout Considerations

The bq2012 measures the voltage differential between
the SR and V

SS

pins. VOS(the offset voltage at the SR
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 (SB and VCC) should be placed as
close as possible to the SB and V

CC

pins, respectively,

and their paths to V

SS

should be as short as possible.
A high-quality ceramic capacitor of 0.1µf is
recommended for V

CC

.

■

The sense resistor (RS) should be as close as possible
to the bq2012.

■

The R-C on the SR pin should be located as close as
possible to the SR pin. The maximum R should not
exceed 100K.

4

bq2012

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

Gas Gauge Operation

The operational overview diagram in Figure 2 illustrates
the operation of the bq2012. The bq2012 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
bq2012 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.

1. Last Measured Discharge (LMD) or learned
battery capacity:

LMD is the last measured discharge capacity of the
battery. On initialization (application of V

CC

or bat

­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.

2. Programmed Full Count (PFC) or initial bat

­tery capacity:

The initial LMD and gas gauge rate values are pro

­grammed by using PROG

1

–PROG4. The PFC also

provides the 100% reference for the absolute dis

­play mode. The bq2012 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.

5

bq2012

FG201002.eps

Rate and

Temperature

Compensation

Temperature

Compensation

Charge
Current

Discharge

Current

Self-Discharge

Timer

Temperature

Translation

Nominal

Available

Charge

(NAC)

Last

Measured

Discharged

(LMD)

Discharge

Count

Register

(DCR)

<

Qualified
Transfer

+

Rate and

Temperature

Compensation

Rate and

Temperature

Compensation

Temperature Step,
Other Data

+

--

+

Inputs

Main Counters

and Capacity

Reference (LMD)

Outputs

Serial

Port

Chip-Controlled

Available Charge

LED Display

Figure 2. Operational Overview

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 =

C

64

Voltage drop over sense resistor = 5mV to 200mV

Therefore:

2200mAh*0.1Ω= 220mVh

Select:

PFC = 33792 counts or 211mVh
PROG

1

= float

PROG

2

= float

PROG

3

= float

PROG

4

= low

PROG

5

= float

PROG

6

= float

The initial full battery capacity is 211mVh
(2110mAh) until the bq2012 “learns” a new capac

­ity with a qualified discharge from full to EDV1.

6

bq2012

PROG

x

Programmed

Full

Count

(PFC)

PROG

4

= L PROG4= Z

Units

1 2 PROG

3

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

-- -

Scale =

1/80

Scale =

1/160

Scale =

1/320

Scale =

1/640

Scale =

1/1280

Scale =

1/2560

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

V

SR

is equivalent to 2

counts/sec. (nom.)

90 45 22.5 11.25 5.56 2.8 mV

Table 2. bq2012 Programmed Full Count mVh Selections

Pin

Connection

PROG

5

Self-Discharge Rate

PROG

6

Display Mode

DISP

Display State

H Self-discharge disabled NAC = PFC on reset LED disabled

Z

NAC

64

Absolute

LED enabled on discharge when

V

SRO

< -4mV or during a valid charge

L

NAC

47

Relative LED on

Note: PROG5and PROG6states are independent.

Table 1. bq2012 Programming