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Description:
BQ2011SN Gas Gauge IC for High Discharge Rates
Prototype PCB
Part No.:   BQ2011SN
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Description:   Gas Gauge IC for High Discharge Rates
File Size :   195 K    
Page : 21 Pages
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Maker   TI [ TEXAS INSTRUMENTS ]http://www.ti.com
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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 V
CC
momentarily drops below
3.0V. V
CC
is output on RBI when V
CC
is above 3.0V.
After V
CC
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
3x
4x
5x
6x
7x
8x
9x
Ax
Bx
Cx
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
Voltage Thresholds
In conjunction with monitoring V
SR
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
RB
2
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). 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:
V
EDV
= 0.90V
V
MCV
= 2.00V
During discharge and charge, the bq2011 monitors V
SR
for various thresholds, V
SR1
–V
SR4
. 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 V
SR
> V
SR1
(50mV typical)
and resumes 1 second after V
SR
drops back below V
SR1
.
Layout Considerations
The bq2011 measures the voltage differential between
the SR and V
SS
pins. V
OS
(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
Reset
The bq2011 recognizes a valid battery whenever V
SB
is
greater than 0.1V typical. V
SB
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.
The capacitors (SB and V
CC
) 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 (R
S
) should be as close as possible
to the bq2011.
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.
n
Temperature
n
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
4
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