We have developed a carrier board for the verdin family. I have noticed that the SOM is not recharging the rechargeable lithium coin cell for RTC backup. Is there a setting in the IMX8M+ that needs to be set to enable this charging.
The Circuit is set up as described in the IMX8M+ datasheet with a 47kohm resistor between VCC_Backup (pin 249) at the SOM and the coin cell.
I am seeing the voltage at the coin cell approximately 0.011V higher than the voltage measured on the other side of the resistor.
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Hi George,
RTC Backup Battery Charging on Verdin iMX8M Plus
Based on the Verdin iMX8M Plus V1.1 datasheet, the RTC charging functionality should work automatically when the module’s main voltage is available(1).
How the RTC Charging Works
The onboard RTC on the Verdin iMX8M Plus is designed to automatically recharge a supercapacitor or rechargeable battery via the VCC_BACKUP pin when the module’s main voltage is present(1). The charging current is intentionally limited to less than 500µA at 3V(1).
Circuit Requirements
Your circuit setup appears correct according to the datasheet specifications(1):
47kΩ current-limiting resistor between the battery and VCC_BACKUP
Connection to VCC_BACKUP (pin 249)
Important Warning: The datasheet specifically states that when using the recharging capabilities, a current-limiting resistor with a value >47kΩ must be added between the battery and VCC_BACKUP(1). If a resistor with lower resistance is used, the module will fail to boot(1).
Troubleshooting Your Issue
The voltage difference you’re measuring (0.011V) across the 47kΩ resistor suggests there is minimal current flow. Here are some considerations:
Check Main Power Supply: The RTC charging only occurs when the module’s main power supply is provided(1)
Battery State: If your rechargeable coin cell is already near full charge, the charging current will be very low
Higher Charging Current: If you need higher charging current, the datasheet mentions it’s possible to implement a charging circuit on the carrier board(1)
No Software Configuration Required
The RTC charging functionality appears to be hardware-controlled and automatic - there’s no mention in the documentation of software settings required to enable this feature(1).
If the charging still isn’t working as expected, you may want to verify that your rechargeable coin cell is functioning properly and that the main power supply to the module is stable.
Best regards, Toradex AI Assistant.
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What is the voltage of the RTC battery you are currently measuring?
Also, which version of the Verdin iMX8MP are you using? Could you provide me with the serial number or full product name as printed on the label?
