Datasheet

BAT-
Powersupplyground
bq24401groundandBAT-
SNS
R
f
C
f
1
2
bq24401
V
SS
R
SNS
MAX
SNS
0.05
I =
R
C
HYS
Hysteresis (V) = V
CC
(C + C )
HYS f
´
BAT+
Q1
FMMT718
D2
ZHCS1000
L1
47 Hm
C9
1000PF
R12
120 W
Q2
MMBT3904LT1
C6
47 Fm
D5
MMSD914LT
D3
MMSD914LT
D4
S1A
DC-
R10
1KW
D1
RED
R2
2KW
C3
10 Fm
D6
BZT52-C5V1
R1
100KW
RC
6
LED
3
BAT
4
VSS
2
TS
5
VCC
7
SNS
1
MOD
8
U1
bq24401
C4
0.0022 Fm
R4
12.4KW
VCC
C7
4.7PF
C8
0.33 Fm
Q3
MMBT3904LT1
R11
220 W
R6
210KW
C5
10 Fm
BAT-
THERM
R7
105KW
R5
20KW
C1
0.1 Fm
R8
6.81KW
C2
0.1 Fm
NOTES: 1. DCinputvoltage:9–16V
3.L1:3L GlobalP/NPKSMD-1005-470K-1A
2.Chargecurrent:1A
R13
1.1KW
R3
0.05 W
DC+
bq24401
SLUS497A –SEPTEMBER 2001–REVISED MARCH 2010 www.ti.com
Figure 6. Current-Sensing Circuit
R
SNS
is sized to provide the desired fast-charge current (I
MAX
).
(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
.
(4)
Figure 7. 3-Cell NiCd/NiMH 1A Charger
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