Description

This reference design automatically provides back-up voltages to an E-Meter during a power interruption. While the input voltage is between 10 V to 12 V: two buck controllers (TPS62147: TPS62173) generate 3.9 V at 2 A and 5 V at 150 mA. An optional synchronous boost generates 3.3 V at 50 mA. A discrete charge circuit charges a supercapacitor with a constant current up to an adjustable voltage of 2.7 V. When the input voltage fails: a synchronous boost takes over and boosts the supercap voltage to 3.9 V. The supercap capacitance and voltage defines the energy: which is available for the backup. The design enables a stable backup output of 3.9 V at 200 mA for about 70 s until the output voltage drops.