BQ2011K datasheet(4/20 Pages) TI

4 / 20 page

ternal bq2011K registers when VCC momentarily drops be-

low 3.0V. VCC is output on RBI when VCC is above 3.0V.

After VCC rises above 3.0V, the bq2011K checks the internal

registers for data loss or corruption. If data has changed,

then the NAC register is cleared, and the LMD register is

loaded with the initial PFC.

Voltage Thresholds

In conjunction with monitoring VSR for charge/discharge

currents, the bq2011K monitors the single-cell battery po-

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

tial 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). The EDV thresh-

old level is used to determine when the battery has

reached an “empty” state, and the MCV threshold is used

for fault detection during charging. The MCV threshold

for the bq2011K is fixed at:

VMCV = 2.00V

The EDV threshold varies as a function of discharge cur-

rent as follows:

Reset

Reset can be accomplished with a command over the se-

rial port as described on page 13.

Temperature

The bq2011K 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 bq2011K 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 bq2011K.

The R-C on the SR pin should be located as close as

possible to the SR pin. The maximum R should not

exceed 20K.

Gas Gauge Operation

The operational overview diagram in Figure 2 illus-

trates the operation of the bq2011K. The bq2011K accu-

mulates a measure of charge and discharge currents, as

well as an estimation of self-discharge. Charge currents

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

bq2011K

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

VSRO (mV)

VEDV (V)

010

<≤

SRO

1.160

<≤

SRO

1.124

<≤

SRO

1.060

<≤

SRO

0.960

SRO > 60

0 (OVLD)

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