Datasheet

 
 
SLUS025F − MAY 2001 − REVISED JULY 2002
12
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APPLICATION INFORMATION
Figure 7. Optional Voltage Divider for
Nonstandard Regulation Voltage,
(High-Side Current Sensing)
SNS
BAT
VCC
TS
COMP
CC
VSS
STAT
bq2057
DC+
DC−
BAT+
BAT−
R
SNS
R
B1
R
B2
SNS
BAT
VCC
TS
COMP
CC
VSS
STAT
bq2057
DC+
DC−
BAT+
BAT−
R
B1
R
B2
R
SNS
Figure 8. Optional Voltage Divider for
Nonstandard Regulation Voltage,
(Low-Side Current Sensing)
charge termination and recharge
The bq2057 monitors the charging current during the voltage-regulation phase. The bq2057 declares a done
condition and terminates charge when the current tapers off to the charge termination threshold, I
(TERM)
. A new
charge cycle begins when the battery voltage falls below the V
(RCH)
threshold.
battery temperature monitoring
The bq2057 continuously monitors temperature by measuring the voltage between the TS and VSS pins. A
negative- or a positive-temperature coefficient thermistor (NTC, PTC) and an external voltage divider typically
develop this voltage. (See Figure 9.) The bq2057 compares this voltage against its internal V
(TS1)
and V
(TS2)
thresholds to determine if charging is allowed. (See Figure 10.) The temperature sensing circuit is immune to
any fluctuation in V
CC
, since both the external voltage divider and the internal thresholds (V
(TS1)
and V
(TS2)
)
are referenced to VCC.
The resistor values of R
(T1)
and R
(T2)
are calculated by the following equations:
For NTC Thermistors
R
T1
+
5 R
TH
R
TC
3
ǒ
R
TC
* R
TH
Ǔ
R
T2
+
5 R
TH
R
TC
ƪ
ǒ
2 R
TC
Ǔ
–
ǒ
7 R
TH
Ǔ
ƫ
(3)
(4)