19-2830; Rev 0; 4/03
Synchronizable, High-Frequency Current- and
Voltage-Mode PWM Controllers for Isolated Supplies
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 9Ω 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
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
Isolated DC-to-DC Modules (Bricks)
Cellular Base Stations
Telecom and Network Systems
High-Performance Off-Line AC/DC Converters
Functional Diagrams and Typical Operating Circuit appear
at end of data sheet.
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
o Clean Startups with High-Capacitance Loads
o Programmable Under/Overvoltage Protection
o Current-Mode, Adjustable Slope Compensation
o Voltage-Mode, Adjustable Ramp Magnitude
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
-40°C to +85°C
-40°C to +85°C
Pin Configurations continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
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.