7.1 Overview

The TPS61390 is a fully integrated boost converter with an 85-V FET to convert a low input voltage to a higher voltage for biasing the APD. The TPS61390 supports an input voltage ranging from 2.5 V to 5.5 V. The device operates at a 700 kHz pulse-width modulation (PWM) crossing the whole load range.

The device can accurately mirror the APD current ranging from 0.5 uA to 2 mA. There are two ratio options for the current proportional to APD current: the MON1 (4 : 5) and MON2 (1 : 5). By connecting a resistor from the mirror output (MON1 or MON2) to GND, the current flowing through the APD is converted into the voltage crossing the resistor from MON1 / MON2 to GND.

With the sample / hold circuitry built-in and triggered by an external sampling clock, the current mirror signal (voltage) is transferred and stored on the holdup capacitor, the voltage on the holdup capacitor is then passed over to the output of an operational amplifier. An external ADC can sense the voltage of the output of the operational amplifier to measure the optical intensity.

Additionally, a high power optical protection is integrated by clamping the pre-set current limit (program by the I_SHORT resistor). The response time of the high optical power is typically 0.5 µs. The device could recovery automatically when the high optical power is removed.

The device comes in a 3-mm × 3-mm QFN package with the operating junction temperature covering from –40°C to 125°C.