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ST unveils ultra-economical synchronous-rectification controllers

STMicroelectronics has unveiled the SRK1000A and SRK1000B, secondary-side synchronous-rectification (SR) controllers for flyback converters.

These devices provide high efficiency and low power consumption and introduce a more affordable and smaller-footprint option for battery chargers, quick chargers, adapters, and USB power-delivery outlets.

Designed for fast turn-on with minimum delay, and with innovative adaptive turn-off logic, the devices maximise synchronous-rectification MOSFET conduction time while reducing the effects of parasitic inductance in the circuit without the need to add external components, leading to improved system efficiency and a reduced bill of materials.

The SRK1000A and SRK1000B are both able to manage a wide range of flyback controllers including quasi-resonant (QR) and mixed CCM/DCM fixed frequency operation up to 300kHz, simplifying system design. Both devices allow programmable blanking time after turn-on (TON), via resistor selection, to prevent noise from inducing spurious behaviour. The SRK1000A has a 2μs fixed blanking time after turn-off (TOFF), while the corresponding value for the SRK1000B is 3μs.

The devices both offer an efficient low power mode at light load, entering a low-consumption sleep mode when synchronous rectification is no longer beneficial. This is managed either by detecting primary-side controller burst-mode operation, or when the SR MOSFET conduction becomes lower than the programmed minimum TON. The device quiescent current in this low consumption mode is only 160μA.

Suitable for applications with output voltage up to 19V, and capable of maintaining regulation down to 2V output in CCM, the SRK1000A and SRK1000B have a wide supply-voltage range of 4.5V to 32V, with a drain-source voltage rating of 100V. The output can sink up to 1A and source up to 0.6A to control the gate of the external N-channel synchronous-rectification MOSFET.

The SRK1000A are SRK1000B are both available in a 2.9mm x 2.8mm 6-pin SOT23-6L packages.

Author
Neil Tyler

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