Current-mode PWM controller with active-clamp architecture and spread spectrum operation

Maxim has unveiled the MAX5974A/MAX5974B/MAX5974C/MAX5974D, 25W to 50W active-clamped, self-driven syncchronous rectification forward converters in continuous-conduction mode. Maxim says that the device's active-clamp topology delivers and efficiency of better than 90% efficiency, thus reducing power consumption in synchronous forward/flyback power supplies targeting IEEE 802.3af/at power devices (PDs). These converters are targeted for applications such as PoE PDs namely IP phones, IP cameras, and wireless LAN access nodes. The MAX5974 is also well-suited for universal and telecom input ranges.

The MAX5974A/MAX5974C versions are well suited for universal rectified offline (85V to 265V) or telecom (36V to 72V) input voltages.
The MAX5974B/MAX5974D also accommodate input voltages as low as 10.5V (e.g., wall adapters).

The MAX5974A/MAX5974B contain an internal sample-and-hold error amplifier that regulates the output voltage through a coupled inductor. This feedback configuration saves space and cost by eliminating the need for a shunt regulator, optocoupler, and tertiary winding for the bias circuit. Applications requiring optocoupler feedback can use the MAX5974C/MAX5974D, which have a continuously connected feedback input.

The device's switching frequency is adjustable from 100kHz to 600kHz and is trimmed to provide ±8% accuracy. This allows designers to optimize the magnetics and filter elements used in the circuit to meet EMI requirements. The duty cycle can be programmed up to 80% of the maximum duty-cycle limit.

Additional features include an enable input to shutdown the device and programmable soft-start to eliminate output-voltage overshoot. The MAX5974A/MAX5974C have an internal bootstrap ULVO with high hysteresis that requires 20V for startup; the MAX5974B/MAX5947D require 10V for startup.

Package: 3mm x 3mm, 16-pin TQFN

Operating temperature range: -40°C to +85°C package.

Price: starts at US$1.07