Micrel, Inc.

MIC5018

April 2006

5

M9999-042406

(408) 955-1690

Functional Diagram

CHA RG E

PUMP

EN

VS

CTL

R2

15k

R1 2k

GND

G

MIC5018

+2.7V to +9V

On

Off

I1

20µA

D1

16V

D2

35V

Q1

Q2

Q3

D3 16V

Functional Diagram with External Components

(High-Side Driver Configuration)

Functional Description

Refer to the functional diagram.

The MIC5018 is a noninverting device. Applying a logic

high signal to CTL (control input) produces gate drive

output. The G (gate) output is used to turn on an

external N-channel MOSFET.

Supply

VS (supply) is rated for +2.7V to +9V. An external

capacitor is recommended to decouple noise.

Control

CTL (control) is a TTL compatible input. CTL must be

forced high or low by an external signal. A floating input

may cause unpredictable operation.

A high input turns on Q2, which sinks the output of

current source I1, making the input of the first inverter

low. The inverter output becomes high enabling the

charge pump.

Charge Pump

The charge pump is enabled when CTL is logic high.

The charge pump consists of an oscillator and voltage

quadrupler (4×). Output voltage is limited to 16V by a

zener diode. The charge pump output voltage will be

approximately:

The oscillator operates from approximately 70kHz to

approximately 100kHz depending upon the supply

voltage and temperature.

Gate Output

The charge pump output is connected directly to the G

(gate) output. The charge pump is active only when CTL

is high. When CTL is low, Q3 is turned on by the second

inverter and discharges the gate of the external

MOSFET to force it off.

If CTL is high, and the voltage applied to VS drops to

zero, the gate output will be floating (unpredictable).

ESD Protection

D1 and D2 clamp positive and negative ESD voltages.

R1 isolates the gate of Q2 from sudden changes on the

CTL input. Q1 turns on if the emitter (CTL input) is

forced below ground to provide additional input

protection. Zener D3 also clamps ESD voltages for the

gate (G) output.