Datasheet
9
LT1161
1161fa
APPLICATIONS INFORMATION
WUU
U
10µF
R
S1
0.2Ω
R
S2
0.02Ω
1µF
1161 F09b
15V
1N4744
15V
1N4744
1N4148
51Ω
51Ω
51Ω
LT1161
8V TO 24V
V
+
V
+
DS1
G1
G2
DS2
HV
LOAD
HV
LOAD
T1
1µF
T2
IRF630
IRF630
HV
2N2222
–
+
1/2
LT1013
2N2222
Figure 9b. Low-Side Drivers with Two Approaches
for Source Current Sensing
Current sensing for protecting low-side drivers can be
done in several different ways. In the Figure 9a circuit, the
supply voltage for the load is assumed to be within the
supply operating range of the LT1161. This allows the load
to be returned to supply through current-sense resistor
R
S
, providing normal operation of the LT1161 protection
circuitry.
If the load cannot be returned to supply through R
S
, or the
load supply voltage is higher than the LT1161 supply, the
current sense must be moved to the source of the low-side
MOSFET. Figure 9b shows two approaches to source
sensing. On channel 1, current limit occurs when the
voltage across sense resistor R
S1
thresholds the V
BE
of the
NPN transistor, causing the LT1161 drain sense pin to be
pulled down.
The channel 2 circuit of Figure 9b uses an operational
amplifier (must common mode to ground) to level shift the
voltage across R
S2
up to the drain sense pin. This ap-
proach allows the use of a much smaller sense resistor
which could be made from PC trace material. In both
cases, the LT1161 restart timers function the same as in
high-side switch applications.
TYPICAL APPLICATIONS
U
1µF
LT1161
1161 TA05
IRFZ44
IRFZ44
IRFZ44
24V
R
S
INPUTS
(MAY BE PARALLELED)
GND
T1
IN1
T2
IN2
T3
IN3
T4
IN4
GND
V
+
DS1
G1
DS2
G2
DS3
G3
DS4
G4
V
+
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
10µF
50V
OUTPUTS
(MAY BE PARALLELED)
15k
100k
Using an Extra Channel to Do Common Current Limit for Multiple/Paralleled Switches