bq2057, bq2057C
bq2057T, bq2057W
SLUS025F − MAY 2001 − REVISED JULY 2002
APPLICATION INFORMATION
Q1
SI6475DQ
PACK+
C2
0.1
µF
PACK−
U1
bq2057
CC
SNS
VCC
VSS
R4
511
Ω
C1
0.1
µF
U2
R5
1 kΩ
COMP
BAT
TS
STAT
RT2
TEMP
RT1
NTC
Battery
Pack
D1
DC+
RSNS
0.2
Ω
R2
1 kΩ
R3
1 kΩ
CMD67−
22SRUC
GND
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:
V
R
SNS
+
I
(SNS)
(1)
O(REG)
Where I
O(REG)
is the desired charging current.
10
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