Datasheet

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SLUS462E − SEPTEMBER 2000 − REVISED NOVEMBER 2004
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14
Charge Qualification and Preconditioning
The bq2400x starts a charge cycle when power is applied
while a battery is present. Charge qualification is based on
battery voltage and the APG/THERM input.
As shown in the block diagram, the internal LowV
comparator output prevents fast-charging a deeply
depleted battery. When set, charging current is provided
by a dedicated precharge current source. The precharge
timer limits the precharge duration. The precharge current
also minimizes heat dissipation in the pass element during
the initial stage of charge.
The APG/THERM input can also be configured to monitor
either the adapter power or the battery temperature using
a thermistor. The bq2400x suspends charge if this input is
outside the limits set by the user. Please refer to the
APG/THERM input section for additional details.
APG/THERM Input
The bq400x continuously monitors temperature or system
input voltage by measuring the voltage between the
APG/THERM (adapter power good/thermistor) and GND.
For temperature, a negative- or a positive- temperature
coefficient thermistor (NTC, PTC) and an external voltage
divider typically develop this voltage (see Figure 16). The
bq2400x compares this voltage against its internal V
TP1
and V
TP2
thresholds to determine if charging is allowed.
(See Figure 17.)
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
bq24002PWP
TEMP
PACK+
PACK−
RT1
C3
0.22 µF
+
−
Battery Pack
RT2
NTC Thermistor
Figure 16. Temperature Sensing Circuit