BQ24401_15 Datasheet, PDF (10/27 Pages) Texas Instruments – Programmable NiCd/NiMH Fast-Charge Management IC

bq24401
SLUS497A – SEPTEMBER 2001 – REVISED MARCH 2010
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BAT-
R_f
R_SNS
1 _SNS
Cf
2 _VSS
Power supply ground
bq24401 ground and BAT-
bq24401
Figure 6. Current-Sensing Circuit
R_SNS is sized to provide the desired fast-charge current (I_MAX).
0.05
I_MAX
=
R_SNS
(3)
If the voltage at the SNS pin is greater than V_SNSLO or less than V_SNSHI, the bq24401 switches the MOD output
high to pass charge current to the battery. When the SNS voltage is less than V_SNSLO or greater than V_SNSHI, the
bq24401 switches the MOD output low to shut off charging current to the battery. A hysteresis capacitor (C_HYS) is
required between the C_MOD pin and the SNS pin to add a healthy amount of hysteresis to the current sense
signal (see Figure 7). Typical hysteresis values are between 5 and 25 mV. The amount of hysteresis can be
calculated by examining the capacitive divider formed by C_HYS and C_f.
Hysteresis (V) = VCC
´
CHYS
(CHYS + Cf )
(4)
DC+
D3
MMSD914LT
D4
S1A
C6
47 mF
Q1
FMMT718
Q2
MMBT3904LT1
L1
47 mH
D2
ZHCS1000
R10
1 KW
D5
MMSD914LT
C9
R12
120 W
1000 PF
VCC
D6
BZT52-C5V1
R2
2 KW
D1
RED
C2
0.1 mF
C3
10 mF
C7
C4
4.7 PF
0.0022 mF
R1
C8
0.33 mF
R4
12.4 KW
U1
1
2
3
4
SNS
VSS
LED
BAT
100 KW
MOD
VCC
RC
TS
8
7
6
5
bq24401
C1
0.1 mF
R8
6.81 KW
R5
20 KW
Q3
MMBT3904LT1
R11
220 W
R6
210 KW
BAT+
C5
10 mF
THERM
R7
105 KW
BAT-
R13
1.1 KW
DC-
NOTES: 1. DC input voltage: 9–16V
2. Charge current: 1A
3. L1: 3L Global P/N PKSMD-1005-470K-1A
Figure 7. 3-Cell NiCd/NiMH 1A Charger
R3
0.05 W
10
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