Datasheet

 
 
SLUS025F − MAY 2001 − REVISED JULY 2002
10
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APPLICATION INFORMATION
CC
SNS
VCC
VSS
COMP
BAT
TS
STAT
bq2057
D1
U2
R3
1 kΩ
R
T2
R
T1
TEMP
PACK−
PACK+
C2
0.1 µF
NTC
Battery
Pack
DC+
R
SNS
0.2 Ω
CMD67−
22SRUC
R5
1 kΩ
R2
1 kΩ
R4
511 Ω
C1
0.1 µF
Q1
SI6475DQ
GND
U1
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:
R
SNS
+
V
(SNS)
I
O(REG)
Where I
O(REG)
is the desired charging current.
(1)