The XCZU28DR RFSoC U1 implements bitstream encryption key technology. The ZCU111 board provides the encryption key backup battery circuit shown in This Figure .
The Seiko TS518FE rechargeable 1.5V lithium button-type battery B1 is soldered to the board with the positive output connected to the XCZU28DR-2E RFSoC U1 V CC_PSBATT pin Y23. The battery supply current I BATT specification is 150 nA maximum when board power is off. B1 is charged from the UTIL_1V8 1.8V rail through a series diode with a typical forward voltage drop of 0.38V and 4.7 ΩK current limit resistor. The nominal charging voltage is 1.42V.