BQ2050H_15 Datasheet, PDF (4/30 Pages) Texas Instruments – Low-Cost Lithium Ion Power Gauge™ IC

Not Recommended For New Designs
bq2050H
Voltage Thresholds
In conjunction with monitoring V_SR for charge/discharge
currents, the bq2050H monitors the battery potential
through the SB pin. The voltage is determined through
a resistor-divider network per the following equation:
RB1 _{= 4N − 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)
thresholds. The EDV threshold levels are used to deter-
mine when the battery has reached an “empty” state.
The EDV thresholds for the bq2050H are programmable
with the default values fixed at:
EDV1 (first) = 0.76V
EDVF (final) = EDV1-0.025V = 0.735V
If V_SB is below either of the two EDV thresholds, the as-
sociated flag is latched and remains latched, independ-
ent of V_SB, until the next valid charge. The V_SB value is
also available over the serial port.
During discharge and charge, the bq2050H monitors
V_SR for various thresholds used to compensate the
charge counter. EDV monitoring is disabled if the dis-
charge rate is greater than 2C (OVLD Flag = 1) and re-
sumes ¹² second after the rate falls below 2C.
RBI Input
The RBI input pin is intended to be used with a storage
capacitor or external supply to provide backup potential
to the internal bq2050H registers when V_CC drops below
3.0V. V_CC is output on RBI when V_CC is above 3.0V. If us-
ing an external supply (such as the bottom series cell) as
the backup source, an external diode is required for isola-
tion.
Reset
The bq2050H can be reset by removing V_CC and ground-
ing the RBI pin for 15 seconds or by commands over the
serial port. The serial port reset command sequence re-
quires writing 00h to register PPFC (address = 1Eh) and
then writing 00h to register LMD (address = 05h).
Temperature
The bq2050H internally determines the temperature in
10°C steps centered from approximately -35°C to +85°C.
The temperature steps are used to adapt charge and dis-
charge rate compensations, self-discharge counting, and
available charge display translation. The temperature
range is available over the serial port in 10°C incre-
ments as shown in the following table:
TMP (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 bq2050H 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:
I The capacitors (C1 and C2) should be placed as
close as possible to the V_CC and SB 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.
I The sense-resistor capacitor should be placed as close
as possible to the SR pin.
I The sense resistor (R_S) should be as close as possible to
the bq2050H.
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