9

LT1161

10

µF

0.2

Ω

0.02

Ω

1

µF

1161 F09b

15V

1N4744

15V

1N4744

1N4148

51

Ω

51

Ω

51

Ω

LT1161

8V TO 24V

DS1

G1

G2

DS2

+

HV

LOAD

HV

LOAD

T1

1

µF

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

circuitry.

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

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

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.

+

1

µF

LT1161

1161 TA05

IRFZ44

IRFZ44

IRFZ44

24V

INPUTS

(MAY BE PARALLELED)

GND

T1

IN1

T2

IN2

T3

IN3

T4

IN4

GND

DS1

G1

DS2

G2

DS3

G3

DS4

G4

1

2

3

4

5

6

7

8

9

10

20

19

18

17

16

15

14

13

12

11

10

µF

50V

OUTPUTS

(MAY BE PARALLELED)

15k

100k

+

Using an Extra Channel to Do Common Current Limit for Multiple/Paralleled Switches