STMicroelectronics STACF01A/STACF01B Flyback Controller ICs

STMicroelectronics STACF01A/STACF01B Active Clamp Flyback Controller ICs drive and control active clamp flyback converters with non-complementary driving of the active clamp (high-side, HS) switch. It is intended explicitly for high-performance AC-DC adapters with GaN HEMTS rated up to 100W and beyond, aimed at high efficiency and power density. The ICs seamlessly change operating mode with loading conditions to optimize efficiency under an extremely wide range of loads: variable frequency with frequency foldback at heavy-medium load, bottom-clamped, load-proportional frequency at light load, burst mode at very light, and no-load.

An automatic adjustment mechanism ensures the reverse primary current needed to achieve ZVS is correctly set for any input/output voltage combination. These ICs can achieve output voltage regulation from the secondary side via optocoupler-based feedback. The ICs are provided with an embedded high-voltage startup circuit that implements the line voltage monitoring system. The STMicroelectronics STACF01A also discharges the X capacitors when the converter gets disconnected from the AC power line. The STACF01B is intended for DC inputs, like SMPS with PFC in front or supplied by a DC bus.

The ICs incorporate two low-side, low-power drivers intended to drive the inputs of an external high-voltage half-bridge driver IC or a SiP such as one of the MasterGaN families. These also provide an extensive set of protection features against primary and secondary side faults (two-level overcurrent, overpower, overload, short circuit, brownout, output overvoltage). A general protection input (active low latch type and active high auto restart) helps implement an external OTP, an external input OVP, or general-purpose protection.

Features

Non-complementary control of active clamp flyback converter
Multimode operation optimizes efficiency over a very wide load range
Up to 500kHz operating frequency with programmable deadtime
Automatic reverse current control for ZVS of low-side switch
ZCD circuit for demagnetization instant detection and OVP setting
Embedded high-voltage startup and active x-cap discharge circuit

Integrated buck-boost regulator for a wide output voltage range
Very low quiescent current enables ultra-low no-load input power
Full set of protection features
Interface with PFC controller
Dual low-side driver and enable for easy pairing with MasterGaN family, other types of GaN power IC, or half-bridge driver IC