BQ24004 Datasheet, PDF (14/22 Pages) Texas Instruments – TWO-CELL Li-ION CHARGE MANAGEMENT IC FOR PDAs AND INTERNET APPLIANCES

bq24004
bq24005
bq24006
SLUS476B – DECEMBER 2000 – REVISED MAY 2002
www.ti.com
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
U1
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.)
1
N/C
20
N/C
2
IN
19
OUT
3
IN
18
OUT
4
VCC
17
VSENSE
5
ISNS
16
AGND
6
N/C
15
STAT2
7
14
APG/THM STAT1
8
EN
13
TMR SEL
9 _VSEL
CR ¹²
10 _GND
N/C ¹¹
PACK+
PACK–
C3
0.22 µF
TEMP
+
–
NTC Thermistor
Battery Pack
bq24005PWP
RT1
RT2
Figure 16. Temperature Sensing Circuit
14