6pin synchronous rectification controllers add adaptive logic
STMicroelectronics has launched two secondary-side synchronous rectification (SR) controllers for flyback converters in a smaller 6pin package.
The smaller footprint of the SRK1000A and SRK1000B controllers and 300kHz switching frequency reduce the size of battery chargers, quick chargers, external power adapters and USB power-delivery outlets.
The controllers are designed for fast turn-on with minimum delay by using adaptive turn-off logic. This maximizes the synchronous-rectification MOSFET conduction time and minimizes the effects of parasitic inductance in the circuit without the need to add external components, improving the efficiency and reducing the 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 behavior. 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.
The synchronous rectification controllers are suitable for applications with output voltage up to 19V, and capable of maintaining regulation down to 2V output in CCM. They 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 package, priced from $0.26 for orders of 1000 pieces.
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