BQ2011_15 Datasheet, PDF (4/26 Pages) Texas Instruments – Gas Gauge IC for High Discharge Rates

bq2011
Register Backup
The bq2011 RBI input pin is intended to be used with a
storage capacitor to provide backup potential to the inter-
nal bq2011 registers when VCC momentarily drops below
3.0V. VCC is output on RBI when VCC is above 3.0V.
After VCC rises above 3.0V, the bq2011 checks the inter-
nal registers for data loss or corruption. If data has
changed, then the NAC and FULCNT registers are
cleared, and the LMD register is loaded with the initial
PFC.
charge display translation. The temperature range is
available over the serial port in 10°C increments as
shown below:
TMPGG (hex)
0x
1x
2x
Temperature Range
< -30°C
-30°C to -20°C
-20°C to -10°C
Voltage Thresholds
3x
-10°C to 0°C
In conjunction with monitoring VSR for charge/discharge
currents, the bq2011 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_{1 = N − 1}
RB₂
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 EDV and MCV
thresholds for the bq2011 are fixed at:
VEDV = 0.90V
VMCV = 2.00V
During discharge and charge, the bq2011 monitors VSR
for various thresholds, VSR1–VSR4. These thresholds are
used to compensate the charge and discharge rates. Ref-
er to the discharge compensation section for details.
EDV monitoring is disabled if VSR > VSR1 (50mV typical)
and resumes 1 second after VSR drops back below VSR1.
Reset
The bq2011 recognizes a valid battery whenever VSB is
greater than 0.1V typical. VSB rising from below 0.25V
resets the device. Reset can also be accomplished with a
command over the serial port as described in the Reset
Register section.
Temperature
The bq2011 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
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 bq2011 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:
n _{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 0.1µf is recommended
for VCC.
n _{The sense resistor (RS) should be as close as possible}
to the bq2011.
n _{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.
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