October 1998

5-177

MIC5021

Micrel

5

Remote Overcurrent Limiting Reset

In circuit breaker applications where the MIC5021 maintains

an off condition after an overcurrent condition is sensed, the

C

Input

Gnd

Gate

Sense

Sense

TTL Input

N-Channel

Power

MOSFET

+12V to +20V

MIC5021

1

2

3

4

8

7

6

5

10µF

0.01

µF

74HC04

(example)

2N3904

Q1

10k to

100k

Retry (H)

Maintained (L)

Figure 11. Remote Control Circuit

Switching Q1 on pulls C

output off when an overcurrent is sensed. Switching Q1 off

causes C

20

µs and continues to retry until the overcurrent condition is

removed.

For demonstration purposes, a 680

Ω load resistor and 3Ω

sense resistor will produce an overcurrent condition when the

load’s supply (V+) is approximately 12V or greater.

Low-Temperature Operation

As the temperature of the MIC5021AJB (extended tempera-

ture range version—no longer available) approaches –55

°C,

the driver’s off-state, gate-output offset from ground in-

creases. If the operating environment of the MIC5021AJB

includes low temperatures (–40

°C to –55°C), add an external

2.2M

Ω resistor as shown in Figures 12a or 12b. This assures

that the

driver’s gate-to-source voltage is far below the

external MOSFET’s gate threshold voltage, forcing the

MOSFET fully off.

Input

Gnd

Gate

Sense

Sense

TTL Input

+12V to +36V

MIC5021AJB

1

2

3

4

8

7

6

5

10µF

2.7

nF

2.2M

add resistor for

–40

°C to –55°C

operation

Figure 12a. Gate-to-Source Pull Down

The gate-to-source configuration (refer to Figure 12a) is

appropriate for resistive and inductive loads.

This also

causes the smallest decrease in gate output voltage.

Input

Gnd

Gate

Sense

Sense

TTL Input

+12V to +36V

MIC5021AJB

1

2

3

4

8

7

6

5

10µF

2.7

nF

2.2M

add resistor for

–40

°C to –55°C

operation

Figure 12b. Gate-to-Ground Pull Down

The gate-to-ground configuration (refer to Figure 12b) is

appropriate for resistive, inductive, or capacitive loads. This

configuration will decrease the gate output voltage slightly

more than the circuit shown in Figure 12a.