High-voltage low-power startup backup battery switch using low voltage devices in 28nm CMOS

This paper presents a 4.8 V tolerant circuit for reliably switching a startup load between a main power supply and a battery power supply. The circuit automatically switches the main power supply over to the battery in case the main line has been interrupted. The circuit includes a pair of back-to-back switch transistors for isolating the load from each power supply, a bias circuit for controlling the switch transistors, two independent current sources and two current subtraction units for deciding which supply to provide to the load. It consumes less than 1 μA per input and it can supply a startup circuitry up to 50 μA. The circuit has been implemented in a CMOS 28 nm technology, using only “low-voltage” devices and was successfully validated in the lab.