DCM PFC controller for offline and industrial supplies
The Analog Devices LT8312IMS#PBF is a power factor controller operating in Discontinuous Conduction Mode (DCM) at a fixed 400 kHz switching frequency.
The 400 kHz fixed switching frequency is a double-edged decision point. In DCM the inductor current resets every cycle, so the core does not accumulate DC flux — that allows a smaller ferrite than a continuous-mode design at the same power. But 400 kHz pushes the switching losses in the MOSFET and the core losses in the inductor; the designer needs to select a fast-recovery diode and a MOSFET with low gate charge and low output capacitance to keep the dissipation manageable. The fixed frequency also simplifies the input EMI filter design because the fundamental and its harmonics are known — no frequency jitter to spread the noise, so the filter corner can be placed just below 400 kHz.
80 µA startup current — sizing the startup resistor
The 80 µA startup current determines the startup resistor value from the rectified DC bus to the VCC pin.
The buyer can qualify this part into a production BOM with confidence that the factory will continue to ship for the foreseeable future. If the application requires a higher temperature grade, the LT8312HMS#PBF sibling extends the operating range to 150°C while keeping the same DCM architecture and 400 kHz switching — the rest of the BOM stays unchanged.