BQ2057DGKR Datasheet, PDF (10/24 Pages) Texas Instruments – ADVANCED LINEAR CHARGE MANAGEMENT IC FOR SINGLE AND TWO CELL LITHIUM-POLYMER

bq2057, bq2057C
bq2057T, bq2057W
SLUS025F − MAY 2001 − REVISED JULY 2002
APPLICATION INFORMATION
DC+
GND
RSNS
D1
0.2 Ω
C1
0.1 µF
Q1
SI6475DQ
R2
1 kΩ
U1
bq2057
CC
COMP
SNS
VCC
VSS
BAT
TS
STAT
R4
511 Ω
R5
1 kΩ
R3
1 kΩ
PACK+
C2
0.1 µF
PACK−
RT1
TEMP
RT2
U2
CMD67−
22SRUC
Battery
Pack
NTC
Figure 4. 0.5-A Charger Using P-Channel MOSFET
current regulation phase
The bq2057 regulates current while the battery-pack voltage is less than the regulation voltage, V_O(REG). The
bq2057 monitors charge current at the SNS input by the voltage drop across a sense-resistor, R_SNS, in series
with the battery pack. In high-side current sensing configuration (Figure 5), R_SNS is between the VCC and SNS
pins, and in low-side sensing (Figure 6) the R_SNS is between VSS (battery negative) and SNS (charger ground)
pins. Charge-current feedback, applied through pin SNS, maintains a voltage of V_(SNS) across the current sense
resistor. The following formula calculates the value of the sense resistor:
RSNS
+
V(SNS)
IO(REG)
(1)
Where I_O(REG) is the desired charging current.
10
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