
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
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
M
Synchronizable, High-Frequency Current- and
Voltage-Mode PWM Controllers for Isolated Supplies
________________________________________________________________
Maxim Integrated Products
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.
1
Ordering Information
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
REF
V
CC
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
EVAVAILABLE
PART
TEMP RANGE
-40
°
C to +85
°
C
-40
°
C to +85
°
C
PIN-PACKAGE
16 QSOP
16 QSOP
MAX8540
EEE
MAX8541
EEE
Functional Diagrams and Typical Operating Circuit appear
at end of data sheet.
Pin Configurations continued at end of data sheet.