The MAX8540/MAX8541 pulse-width-modulated (PWM) controllers for forward/flyback isolated DC-to-DC converters provide maximum flexibility to power-supply designers 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 protection (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 voltage to limit the maximum volt-seconds applied to the transformer primary. The MAX8540EEE allows the user to select the value of slope compensation to further optimize 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 drivers 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 MAX8540EEE 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.
Feature
- 200kHz to 1MHz Adjustable Switching Frequency
- Synchronization to External Clock
- Programmable, Constant Maximum Volt-Second Simplifies Transformer Design
- Programmable Hiccup/Skip Cycles or Latch-Mode Protection
- Clean Startups with High-Capacitance Loads
- Programmable Under/Overvoltage Protection
- Current-Mode, Adjustable Slope Compensation (MAX8540)
- Voltage-Mode, Adjustable Ramp Magnitude (MAX8541)
- 10mA, 5V Regulator
- 75mV to 1.25mV Adjustable Current Limit Reduces External Components
- Internal Gate Driver for Low-Power Applications
- External Gate Driver for High-Power Applications
Applications
- Cell Phone Base Stations
- High-Performance Offline AC/DC Converters
- Isolated DC-to-DC Modules (Bricks)
- Telecom and Network Systems
