STMicroelectronics has introduced the STSR2, a smart driver IC for synchronous rectifiers that includes specialized control circuitry to let designers take advantage of the lower conduction losses offered by MOSFETs and boost the efficiency of their power converter designs.
The STSR2 smart driver IC provides two complementary high-current outputs, able to source 2A and sink 3.5A, to drive the power MOSFETs used as secondary synchronous rectifiers in high-efficiency forward topology with a low output voltage.
Suited to distribute power, telecom and computer server power supplies, the device is designed to derive a reliable synchronization from the secondary side of the transformer. An internal oscillator, coupled with a smart clock detection mechanism, maintains reliable switching operation even in light-load conditions, where false trigger pulses are common. This avoids many of the problems of using self-driven synchronous rectification.
Using a single clock input, the STSR2 provides two driving signals and automatically inserts dead time needed to prevent current shoot-through. By using two resistors, designers can control the turn-off anticipation time of the freewheeling MOSFET in order to optimize converter efficiency.
An inhibit function allows the freewheeling MOSFET to be turned off during light-load conditions. This feature makes discontinuous conduction-mode possible and prevents the freewheeling MOSFET from sinking current from the load.
The STSR2 automatically turns off the outputs when duty-cycle is lower than 13%, but a second version of the driver IC, the STSR2M, works even at very low duty-cycle values.
The STSR2 operates from a 4.5V to 5.5V supply and in the 20kHz to 750kHz frequency range. The built-in UVLO feature guarantees proper startup and avoids undesirable driving when the supply voltage drops. The STSR2 is supplied in an 8-pin small-outline (SO-8) package.
