MIC5021

Micrel

5-170

October 1998

Pin Description

Pin Number

Pin Name

Pin Function

1V

DD

Supply: +12V to +36V. Decouple with

≥ 10µF capacitor.

2

Input

TTL Compatible Input: Logic high turns the external MOSFET on. An

internal pull-down returns an open pin to logic low.

3C

T

Retry Timing Capacitor: Controls the off time (t

retry cycle. (Duty cycle adjustment.)

• Open = approx. 20% duty cycle.

• Capacitor to Ground = approx. 20% to < 1% duty cycle.

• Pull-up resistor = approx. 20% to approx. 75% duty cycle.

• Ground = maintained shutdown upon overcurrent condition.

4

Gnd

Circuit Ground

5

Sense +

Current Sense Comparator (+) Input: Connect to high side of sense resistor

or current sensing MOSFET sense lead. A built-in offset in conjunction with

R

6

Sense –

Current Sense Comparator (–) Input: Connect to the low side of the sense

resistor (usually the high side of the load).

7

Gate

Gate Drive: Drives the gate of an external power MOSFET. Also limits V

GS

to 15V max. to prevent Gate-to-Source damage. Will sink and source

current.

8V

BOOST

Charge Pump Boost Capacitor: A bootstrap capacitor from V

FET source pin supplies charge to quickly enhance the Gate output during

turn-on.

Pin Configuration

1

2

3

4

8

7

6

5

Input

Gnd

Gate

Sense

−

Sense

+

1

2

3

4

8

7

6

5

Gate

Sense

−

Sense

+

Input

Gnd

Block Diagram

Sense –

Sense +

6V Internal Regulator

50mV

Input

ONE-

SHOT

Gate

6V

OFF

ON

Fault

Normal

15V

Q1

CHARGE

PUMP

↓

↑

Transistor: 106

DIP Package

SOIC Package

(N)

(M)