ESP32-P4: How to connect VDD_BAT

On the ESP32-P4, the VDD_BAT pin is an analog power supply pin powering the real-time clock (RTC) and some other low-power analog components of the chip when the main power supply is off.

You must not let the VDD_BAT pin float. If you do not intend to use a battery to power the RTC, you should connect the VDD_BAT pin to the 3.3V supply connected to the VDD_ANA pin.

Connect the VDD_BAT pin to a 3.3V power supply. The permissible voltage range for this pin is from 2.5V to 3.6V (absolute maximum rating of 3.6V). Supplying a higher voltage than 3.6V may destroy the chip.

You can just connect VDD_BAT to the same 3.3V power supply as VDD_LDO and VDD_DCDCC, however, isolating the VDD_BAT and VDD_ANA using a small ferrite bead will increase stability & performance (keep in min)

You may connect a battery (e.g. a 3V coin cell) to the VDD_BAT pin to power the RTC when the main power supply is off, but you must prevent the voltage from exceeding 3.6V! Therefore, you can NOT connect a 3.7V Li-Ion or Li-Po battery directly to the VDD_BAT pin, as this will destroy the chip (since the fully charged voltage of a 3.7V Li-Ion or Li-Po battery is about 4.2V). See the Espressif docs on ESP32-P4 battery backup solutions for more details on how to connect a battery.

You must connect a 100nF and a 10µF decoupling capacitor as close as possible to the VDD_BAT pin and connect between the 3.3V supply and the ground plane.

Source: ESP32-P4 hardware design guide