MAX8540

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

Both controllers MAX8540 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 of MAX8540  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 MAX8540 allows the user to select the value of slope compensation to further optimize magnetics design. The MAX8541 features useradjustable ramp magnitude for the PWM comparator.

A cycle-by-cycle current-limit function of MAX8540 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 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 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.