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| BQ24450 Datasheet, PDF (12/20 Pages) Texas Instruments – INTEGRATED CHARGE CONTROLLER FOR LEAD-ACID BATTERIES | |||
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bq24450
SLUS929 â APRIL 2009 ..................................................................................................................................................................................................... www.ti.com
External
Supply
RISNS
QEXT
DEXT ICHG
VBAT
VRLA
Battery
ISNS 1
Q6
ISNSP
3
ISNSM IFB DRVC
2
4
16
DRVE
15
+
25mV
250mV
Q1
+
RA
RT
COMP
14
VREF
RB
VFB
13
5
IN
Voltage
Reference
VIN
VREF
Q5
Q2 Q3
Q4
11 PRE-CHG RC
12 CE
VREF
8
BSTOP
0.95VREF
0.90VREF
VVFB
7
Q7
10 STAT1
RD
Q8
Charging State Logic
9
Q9
6
GND
Figure 7.
Changing the value of ITAPER for a given IMAX-CHG
In the examples above, ITAPER is 10% of IMAX-CHG, because VILIM is 250mV and VISNS is 25mV (typical values),
and the same resistor is used for both, the taper comparator and the current-loop amplifier. In most applications,
setting ITAPER to 10% of IMAX-CHG is perfectly fine. But if, for some reason, a different value of ITAPER is required, it
can be achieved, as shown in Figure 8(a) and Figure 8(b).
RISNS1 RISNS2
QEXT
RISNS1 RISNS2
QEXT
IN ISNSP
5
3
ISNSM IFB DRVC
2
4
16
IN ISNSP
5
3
IFB
4
ISNSM
2
DRVC
16
Figure 8a
IMAX-CHG = VILIM ¸ (RISNS1 + RISNS2 )
ITAPER = VISNS ¸ RISNS2
Figure 8.
Figure 8b
IMAX-CHG = VILIM ¸ RISNS1
ITAPER = VISNS ¸ (RISNS1 + RISNS2 )
12
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