BQ24004_12 Datasheet, PDF (14/27 Pages) Texas Instruments – TWO-CELL Li-ION CHARGE MANAGEMENT IC

bq24004
bq24005
bq24006
SLUS476F – DECEMBER 2000 – REVISED MAY 2012
If the charger designs incorporate a thermistor, the
resistor divider RT1 and RT2 is calculated by using
the following two equations.
First, calculate RT2.
ƪ ƫ V_B R_H R_C
1
VC
*
1
VH
ǒ Ǔ ǒ Ǔ ^{RT2 +}
R_H
VB
VH
*
1
* R_C
VB
VC
*
1
then use the resistor value to find RT1.
VB
RT1 +
VC
1
RT2
*
)
1
1
RC
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
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bq24005PWP
Figure 18. APG Sensing Circuit
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.
Figure 17. Temperature Threshold
14
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