MIC38HC42/3/4/5

Micrel, Inc.

April 2005

1

M9999-042205

MIC38HC42/3/4/5

BiCMOS 1A Current-Mode PWM Controllers

General Description

The MIC38HC4x family are fixed frequency current-mode

PWM controllers with 1A drive current capability. Micrel’s

BiCMOS devices are pin-compatible with 384x bipolar de-

vices. Their high output drive, with fast rise and fall times,

combined with low startup current make it an ideal PWM

controller where high efficiency is required.

Undervoltage lockout circuitry allows the ’42 and ’44 versions

to start up at 14.5V and operate down to 9V, and the ’43 and

’45 versions start at 8.4V with operation down to 7.6V. All

versions operate up to 20V.

When compared to bipolar UC384x devices operating from a

15V supply, start-up current has been reduced to 50µA

typical and operating current has been reduced to 4.0 mA

typical. Decreased output rise and fall times drive larger

MOSFETs, and rail-to-rail output capability increases effi-

ciency, especially at lower supply voltages. The MIC38HC4x

also features a trimmed oscillator discharge current and

bandgap reference.

MIC38HC4x-1 is available in 14-pin plastic DIP and SOIC

packages. 8-pin devices feature small size, while 14-pin

devices separate the analog and power connections for

improved performance and power dissipation.

Functional Diagram

Features

• Fast 20ns output rise and 15ns output fall times

• –40°C to +85°C temperature range

exceeds UC284x specifications

•High-performance, low-power BiCMOS Process

•Ultralow start-up current (50µA typical)

• Low operating current (4mA typical)

•High output drive (1A peak current, HC version)

• CMOS outputs with rail-to-rail swing

• Current-mode operation up to 500kHz

•Trimmed 5V bandgap reference

•Pin-for-pin compatible with UC3842/3843/3844/3845(A)

•Trimmed oscillator discharge current

• UVLO with hysteresis

• Low cross-conduction currents

Applications

• Current-mode, off-line, switched-mode power supplies

• Current-mode, dc-to-dc converters.

•Step-down “buck” regulators

•Step-up “boost” regulators

•Flyback, isolated regulators

• Forward converters

• Synchronous FET converters

TQ

S

R

Q

R

2R

Oscillator

UVLO

5V

Reference

VDD

7 (12)

VREF

8 (14)

RT/CT

4 (7)

FB

2 (3)

2.5V

COMP

1 (1)

GND*(AGND)

5

(9)

ISNS

3 (5)

(VD)

(11)

OUT

6 (10)

(PGND)

(8)

( ) pins are on MIC38HC4x-1 (14-lead) versions only

* MIC38HC4x (8-lead) versions only

†

MIC38HC42, MIC38HC43 (96% max. duty cycle) versions only

‡

MIC38HC44, MIC38HC45 (50% max. duty cycle) versions only

†

‡

35V

*

*

Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com