The TPS61391 is a 700-kHz pulse-width modulating (PWM) step-up converter with an 85-V switch FET with an input ranging from 2.5 V to 5.5 V. The switching peak current is up to 1000 mA. The TPS61391 includes accurate current mirror with two gain options selectable (1 : 5 or 4 : 5). The TPS61391 also provides high optical-power protection with an additional FET in series with the APD power path with the typical response time of 0.5 µs . It can recover automatically once the high optical releasing. The TPS61391 is available in 3 mm × 3 mm QFN package with exposed pad underneath.