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MIC4416BM4

IttyBitty™ Low-Side MOSFET Driver

Master Instrument Corporation 

MIC4416/4417

Functional Diagram

VSUPPLY

VS

Micrel, Inc.

VSWITCHED

0.3mA

0.6mA

D1

D4

Q2

R1

CTL

2k

Q1

MIC4417

INVERTING

Q3

G

Logic-Level

Input

D2

D3 D5

35V

MIC4416

Q4

NONINVERTING

GND

Functional Diagram with External Components

Functional Description

Refer to the functional diagram.

The MIC4416 is a noninverting driver. A logic high on the CTL

(control) input produces gate drive output. The MIC4417 is

an inverting driver. A logic low on the 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 +4.5V to +18V. External capacitors

are 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 will cause

unpredictable operation.

A high input turns on Q1, which sinks the output of the 0.3mA

and the 0.6mA current source, forcing the input of the first

inverter low.

Hysteresis

The control threshold voltage, when CTL is rising, is slightly

higher than the control threshold voltage when CTL is falling.

When CTL is low, Q2 is on, which applies the additional

0.6mA current source to Q1. Forcing CTL high turns on Q1

which must sink 0.9mA from the two current sources. The

higher current through Q1 causes a larger drain-to-source

voltage drop across Q1. A slightly higher control voltage is

required to pull the input of the first inverter down to its

threshold.

Q2 turns off after the first inverter output goes high. This

reduces the current through Q1 to 0.3mA. The lower current

reduces the drain-to-source voltage drop across Q1. A

slightly lower control voltage will pull the input of the first

inverter up to its threshold.

Drivers

The second (optional) inverter permits the driver to be manu-

factured in inverting and noninverting versions.

The last inverter functions as a driver for the output MOSFETs

Q3 and Q4.

Gate Output

G (gate) is designed to drive a capacitive load. VG (gate

output voltage) is either approximately the supply voltage or

approximately ground, depending on the logic state applied

to CTL.

If CTL is high, and VS (supply) drops to zero, the gate output

will be floating (unpredictable).

ESD Protection

D1 protects VS from negative ESD voltages. D2 and D3

clamp positive and negative ESD voltages applied to CTL.

R1 isolates the gate of Q1 from sudden changes on the CTL

input. D4 and D5 prevent Q1’s gate voltage from exceeding

the supply voltage or going below ground.

May 2005

7

MIC4416/4417

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