General Description

The MAX8540/MAX8541 pulse-width-modulated (PWM)

controllers for forward/flyback isolated DC-to-DC convert-

ers provide maximum flexibility to power-supply design-

ers and reduce external component count. These

controllers allow common PC board layout for current-

mode (MAX8540) and voltage-mode (MAX8541) designs.

Both controllers feature adjustable switching frequency

and external synchronization from 200kHz to 1MHz.

Active-high and active-low enable, undervoltage pro-

tection (UVP), and overvoltage protection (OVP) reduce

external component count.

Maximum duty cycle is adjustable, and the feed-forward

function scales the maximum duty cycle with input volt-

age to limit the maximum volt-seconds applied to the

transformer primary. The MAX8540 allows the user to

select the value of slope compensation to further opti-

mize magnetics design. The MAX8541 features user-

adjustable ramp magnitude for the PWM comparator.

A cycle-by-cycle current-limit function controls the peak

primary current during overload and short circuit. Both

controllers can be set to latch off or to hiccup when a

short circuit is detected. The number of current-limited

cycles to initiate the hiccup mode and number of

cycles skipped are user selectable to allow startup with

high-capacitance loads and protect the converter

against sustained short circuits.

The MAX8540/MAX8541 feature 9

Ω internal gate dri-

vers for low-power applications and are compatible

with external gate drivers for high-power applications.

Both devices are available in the space-saving 16-pin

QSOP package.

The MAX8541 EV kit evaluates the MAX8540 and the

MAX8541 to speed designs. Design examples are also

available in application notes: 50W Voltage-Mode

Forward Converter Design with the MAX8541 and 50W

Current-Mode Forward Converter Design with the

MAX8540.

Applications

Isolated DC-to-DC Modules (Bricks)

Cellular Base Stations

Telecom and Network Systems

High-Performance Off-Line AC/DC Converters

Features

o 200kHz to 1MHz Adjustable Switching Frequency

o Synchronization to External Clock

o Programmable, Constant Maximum Volt-Second

Simplifies Transformer Design

o Programmable Hiccup/Skip Cycles or Latch-Mode

Protection

o Clean Startups with High-Capacitance Loads

o Programmable Under/Overvoltage Protection

o Current-Mode, Adjustable Slope Compensation

(MAX8540)

o Voltage-Mode, Adjustable Ramp Magnitude

(MAX8541)

o 10mA, 5V Regulator

o 75mV to 1.25mV Adjustable Current Limit

Reduces External Components

o Internal Gate Driver for Low-Power Applications

o External Gate Driver for High-Power Applications

Synchronizable, High-Frequency Current- and

Voltage-Mode PWM Controllers for Isolated Supplies

________________________________________________________________ Maxim Integrated Products

1

Ordering Information

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

REF

DRV

GND

SKTON

CS

SKTOFF

ILIM

OPTO

TOP VIEW

MAX8540EEE

QSOP

OV

UV

MAXDTY

FREQ/SYNC

SS

EN

SCOMP

Pin Configurations

19-2830; Rev 0; 4/03

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

EVALUATION

KIT

AVAILABLE

PART

TEMP RANGE

PIN-PACKAGE

MAX8540EEE

-40

°C to +85°C

16 QSOP

MAX8541EEE

-40

°C to +85°C

16 QSOP

Functional Diagrams and Typical Operating Circuit appear

at end of data sheet.

Pin Configurations continued at end of data sheet.