Setting PMIC_BBAT Charging Voltage

[benx0aoa]

Hello,

I am adding a rechargeable coin cell to a custom carrier board, to be connected to the PMIC_BBAT pin:
https://www.digikey.com/en/products/detail/panasonic-bsg/ML-614S-FN/447506?s=N4IgTCBcDaILIBkC0A2AjAFgMoHoBiAciALoC%2BQA

In other forum posts, it is alluded to that a rechargeable battery can be used in the nano dev kit:

How to add a correct battery for RTC on Jetson Nano

Hi, we would like to add a backup battery for the RTC clock for the Jetson Nano Devkit. According to http://www.realtimes.cn/?m=common&a=down&id=13 the J45 mark can be used for that purpose. However, on page 12 it states An optional back up battery can be attached to the PMIC_BBAT module input. It is used to maintain the RTC voltage when VDD_IN is not present. This pin is connected directly to the onboard PMIC. When a backup cell is connected to the PMIC, the RTC will retain its contents and…

Is there any software setup required to use a rechargeable ML battery? The product design guide mentions that the PMIC_BBAT pin can charge a coin cell anywhere between 2.5V and 3.5V, but makes no mention of how to set the output voltage. Is any protection circuitry needed to use a rechargeable coin cell?

Thank you

[ShaneCCC]

Modify below in device tree to configure it.

			backup-battery {
 				maxim,backup-battery-charging-current = <100>;
 				maxim,backup-battery-charging-voltage = <3000000>;
 				maxim,backup-battery-output-resister = <100>;
 			};