MAX5974x Current-Mode PWM Controllers

ADI's MAX5974x provide control for wide-input-voltage, active-clamped, current-mode PWM, forward converters in Power over Ethernet (PoE) powered device (PD) applications. The MAX5974A and MAX5974C are well-suited for universal or telecom input range, while the MAX5974B and MAX5974D also accommodate low input voltage down to 10.5 V.

The devices include several features to enhance supply efficiency. The AUX driver recycles magnetizing current instead of wasting it in a dissipative clamp circuit. Programmable dead time between the AUX and main driver allows zero-voltage switching (ZVS). Under light-load conditions, the devices reduce the switching frequency (frequency foldback) to reduce switching losses.

The MAX5974A and MAX5974B feature unique circuitry to achieve output regulation without using an optocoupler, while the MAX5974C and MAX5974D utilize the traditional optocoupler feedback method. An internal error amplifier with a 1% reference is useful in nonisolated design, eliminating the need for an external shunt regulator.

The devices feature a unique feed-forward maximum duty-cycle clamp that makes the maximum clamp voltage during transient conditions independent of the line voltage, allowing the use of a power MOSFET with lower breakdown voltage. The programmable frequency dithering feature provides low-EMI, spread-spectrum operation.

The MAX5974 are available in 16-pin TQFN-EP packages and are rated for operation over the -40°C to +85°C and -40°C to +125°C temperature ranges.