MIC38C42/3/4/5

Micrel, Inc.

September 2007

1

M9999-091107

MIC38C42/3/4/5

BiCMOS Current-Mode PWM Controllers

General Description

The MIC38C4x are fixed frequency, high performance, cur-

rent-mode PWM controllers. Micrel’s BiCMOS devices are

pin compatible with 384x bipolar devices but feature several

improvements.

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 384x devices operating from a

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

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 efficiency, espe-

cially at lower supply voltages. The MIC38C4x also features

a trimmed oscillator discharge current and bandgap refer-

ence.

The MIC38C4x denotes 8-pin plastic DIP, SOIC, and MSOP

packages. MIC384Cx-1 denotes 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 perfomance and power dissipation.

For fast rise and fall times and higher output drive, refer to

the MIC38HC4x.

Functional Diagram

Features

• Fast 40ns output rise and 30ns output fall times

• –40°C to +85°C temperature range

meets UC284x specifications

• High-performance, low-power BiCMOS Process

• Ultralow start-up current (50µA typical)

• Low operating current (4mA typical)

• CMOS outputs with rail-to-rail swing

• ≥ 500kHz current-mode operation

• 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

T Q

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)

OUT

6 (10)

( )

pins are on MIC38C4x-1 (14-lead) versions only

*

MIC38C4x, (8-lead) versions only

†

‡

(VD)

(11)

(PGND)

(8)

35V

*

*

†

MIC38C42, MIC38C43 (96% max. duty cycle) versions only

‡

MIC38C44, MIC38C45 (50% max. duty cycle) versions only

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