STMicroelectronics RK1000A and SRK1000B synchronous-rectification controllers

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STMicroelectronics’ SRK1000A and SRK1000B secondary-side synchronous-rectification (SR) controllers for flyback converters, featuring high efficiency and low power consumption, offer a small-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 are said to maximise synchronous-rectification MOSFET conduction time and minimise 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. They are available in a 2.9 x 2.8 mm 6-pin SOT23-6L package.

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 300 kHz, simplifying system design. Both devices allow programmable blanking time after turn-on (T_ON), via resistor selection, to prevent noise from inducing spurious behaviour. The SRK1000A has a 2 μs fixed blanking time after turn-off (T_OFF), while the corresponding value for the SRK1000B is 3 μs.

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 T_ON. The device quiescent current in this low-consumption mode is 160 μA.

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

For more information: www.st.com/srk1000a-pr.