BQ2012SN datasheet(4/20 Pages) TI

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Voltage Thresholds

In conjunction with monitoring VSR for 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:

=−

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)

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

sociated flag is latched and remains latched, independ-

ent of VSB, until the next valid charge.

During discharge and charge, the bq2012 monitors VSR

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 VSR

≤ -250mV typical and resumes 1

2 sec-

ond after VSR > -250mV.

EMPTY Output

The EMPTY output switches to high impedance when

VSB <VEDF and remains latched until a valid charge oc-

curs.

The bq2012 also monitors VSB relative to VMCV,

2.25V. VSB falling from above VMCV resets the device.

Reset

The bq2012 recognizes a valid battery whenever VSB is

greater than 0.1V typical. VSB 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 VSS 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 VCC pins, respectively,

and their paths to VSS should be as short as possible.

A high-quality ceramic capacitor of 0.1

µf is

recommended for VCC.

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.

bq2012

TMPGG (hex)

Temperature Range

< -30°C

-30°C to -20°C

-20°C to -10°C

-10°C to 0°C

0°C to 10°C

10°C to 20°C

20°C to 30°C

30°C to 40°C

40°C to 50°C

50°C to 60°C

60°C to 70°C

70°C to 80°C

> 80°C

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