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TM4C129EKCPDT: Power Pin VDD3V3 abnormal when USE VBAT(3.0V) only

Part Number: TM4C129EKCPDT

Dears:

The whole equipment works normally when VBAT pin is powered by CR1220-H (3.0V) and connecting the power supply (VDD3V3/ VDD_MCU in SCH as below);

But disconnecting the power supply(VDD3V3), 1.6VDC is detected on Net VDD3V3 while  powered by CR1220-H (VBAT=3.0V) ONLY.

Below is the hardware circuit , FYI.

For software,