BQ2014_15 Datasheet, PDF (4/27 Pages) Texas Instruments – Gas Gauge IC with External Charge Control

Not Recommended For New Designs
bq2014
Voltage Thresholds
In conjunction with monitoring VSR for charge/discharge
currents, the bq2014 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:
R2 _{= N − 1}
R3
where N is the number of cells, R2 is connected to the
positive battery terminal, and R3 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 bq2014 are programmable
with the default values 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 (as defined in the
section entitled “Gas Gauge Operation”). The VSB value
is also available over the serial port.
During discharge and charge, the bq2014 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 ½ 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.
Reset
The bq2014 recognizes a valid battery whenever VSB is
greater than 0.1V typical. VSB rising from below 0.25V
or falling from above 2.25V (VMCV) resets the device. Re-
set can also be accomplished with a command over the
serial port as described in the Reset Register section.
Temperature
The bq2014 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:
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
Layout Considerations
The bq2014 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 (C2 and C3) 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 (R1, C1) should be placed as close}
as possible to the SR pin.
n _{The sense resistor (R16) should be as close as}
possible to the bq2014.
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