Datasheet

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SLUS462E − SEPTEMBER 2000 − REVISED NOVEMBER 2004
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15
If the charger designs incorporate a thermistor, the resistor
divider RT1 and RT2 is calculated by using the following
two equations.
First, calculate RT2.
RT2 +
V
B
R
H
R
C
ƪ
1
V
C
*
1
V
H
ƫ
R
H
ǒ
V
B
V
H
* 1
Ǔ
* R
C
ǒ
V
B
V
C
* 1
Ǔ
then use the resistor value to find RT1.
RT1 +
V
B
V
C
* 1
1
RT2
)
1
R
C
Where:
V
B
= V
CR
(bias voltage)
R
H
= Resistance of the thermistor at the desired hot trip
threshold
R
C
= Resistance of the thermistor at the desired cold trip
threshold
V
H
= VP2 or the lower APG trip threshold
V
C
= VP2 or the upper APG trip threshold
RT1 = Top resistor in the divider string
RT2 = Bottom resistor in the divider string
GND
V
TP2
V
TP1
Vcc
Normal Temp Range
Temp Fault
Temp Fault
Figure 17. Temperature Threshold Figure 18. APG Sensing Circuit
U1
N/C N/C
120
IN OUT
219
IN OUT
318
V
CC
VSENSE
417
ISNS AGND
516
N/C STAT2
615
APG/THM STAT1
714
VSEL CR
912
EN TMR SEL
813
GND N/C
10 11
DC−
DC+
V
CC
bq24002PWP
R1
R2
Values of resistors R1 and R2 can be calculated using the following equation:
V
APG
+ V
CC
R2
(R1 ) R2)
where V
APG
is the voltage at the APG/THM pin.
Current Regulation
The bq2400x provides current regulation while the battery-pack voltage is less than the regulation voltage. The current
regulation loop effectively amplifies the error between a reference signal, Vilim, and the drop across the external sense
resistor, R
SNS
.