MOSFET speed charging for portable devices
Eight 60V MOSFETs are designed for synchronous rectification in flyback converters, used in quick chargers for portable devices, such as smartphones. The AlphaSGT series from Alpha and Omega Semiconductor is made up of AO4262E, AO4264E, AO4268, AON6262E, AON6264E, AON6268, AON7262E and AON7264E.
They offer three levels of maximum on-resistance at 4.5V gate drive voltage, namely 6.5, 8.5 and 13.5mOhm. The MOSFETs are available in three package types, SO-8, DFN5x6, and DFN3x3.
As higher power charger circuits are being adopted to power mobile devices in a shorter time, driving the demand for higher performance MOSFETs for synchronous rectification. Rather than raise the output voltage of the charger, so that with the same output current, higher power can be delivered to the battery system, these MOSFETs directly increase the output current of the charger circuit. They use a simple circuit design by keeping high current conversion inside the charger. A 60V platform is claimed to offer better on-resistance and voltage tolerance balance. The family is optimised for low on-resistance at a lower gate drive voltage, which is normally around 4.5V for most controllers. Switching losses are dependent on the control scheme used in the charger circuit. The company’s proprietary AlphaSGT process is claimed to provide best-in-class on-resistance with very low parasitic capacitance, which ensures lower switching loss. The devices are also tuned to keep EMI suppression simple and reliable.