Datasheet

Voltage Thresholds
In conjunction with monitoring V
SR
for charge/discharge
currents, the bq2010 monitors the single-cell battery
potential through the SB pin. The single-cell voltage
potential is determined through a resistor/divider net
-
work according to 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 bq2010 are fixed at:
V
EDV1
(early warning) = 1.05V
V
EDVF
(empty) = 0.95V
If V
SB
is below either of the two EDV thresholds, the as-
sociated flag is latched and remains latched, indepen-
dent of V
SB
, until the next valid charge. EDV
monitoring may be disabled under certain conditions as
described in the next paragraph.
During discharge and charge, the bq2010 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
second
after V
SR
> -250mV.
EMPTY Output
The EMPTY output switches to high impedance when
V
SB
<V
EDVF
and remains latched until a valid charge
occurs. The bq2010 also monitors V
SB
relative to V
MCV
,
2.25V. V
SB
falling from above V
MCV
resets the device.
Reset
The bq2010 recognizes a valid battery whenever V
SB
is
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 Reset Register section.
Temperature
The bq2010 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 bq2010 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
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 0.1
µ
f is
recommended for V
CC
.
n
The sense resistor capacitor should be placed as close
as possible to the SR pin.
n
The sense resistor (R
SNS
) should be as close as
possible to the bq2010.
4
bq2010
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