VDD_RTC Function on TX1 SOM

Reading the datasheet it appears that the TX1 SOM has an on-board PMIC MAX77620. I am assuming this is a Maxim part but cannot locate a datasheet anywhere for it. Can you provide it?

Reading from the datasheet for the TX1 SOM it sounds like the RTC pin has battery charging capability using the MAX77260. It mentions it can be set from 2.5V to 3.5V and 50uA to 800uA. I plan to use a Rechargeable Lithium Manganese cell size ML-614 on our own custom board but need some details from the MAX77620 to finalize this.

MAX77620 datesheet should get directly from MAXIM.

Backup Battery Charger in MAX77620 below can be programmable:
output voltage range: typ 2.5/3/3.3/3.5(V)
Constant Current Limit: 50/100/200/400/600/800(uA)
Output Resistance: 0.1/1/3/6(Kohm)

I have looked all over MAXIM site and cannot find the datasheet. Are there registry setting that can be controlled over to the SOM for voltage and current, that is really all we need to know. I have been going through the TX1 datasheet and I am not finding anything specific of how that can be programmed in. Can you point me in the right direction.

Better check how to config this in code.
TX1 soc control PMU by I2C, and here is the MAX77620 BBAT register info.


I suspect you’d need to sign an NDA with Maxim in order to get MAX77620 datasheet and other documentation.

Yes, confirm with Maxim the NDA is needed to request the full datasheet.
Below is Maxim technical support link, customer can submit request from below website.
Once MAXIM got this kind request, they will coordinate the NDA signature, and provide MAX77620 documents.


I see this code in the device tree.

backup-battery {
				maxim,backup-battery-charging-current = <0x64>;
				maxim,backup-battery-output-resister = <0x64>;
				maxim,backup-battery-charging-voltage = <0x2dc6c0>;

Is this configuration used? If so which driver file in the kernel sources uses this?

I am trying to figure out how to increase the charging current for VDD_RTC.

Check the file below.



Thanks. I am looking at max77620.c, I don’t see any code setting the backup-battery-charging-current. Or anything setting the CNFGBBC registers.

But strangely, I was able affect the battery charging by changing the values in that device tree. Although it worked in the wrong direction. I am trying to increase the battery charging current, but setting maxim,backup-battery-charging-current to 0x320 turned it off.


Try this patch for the backup battery.
0001-mfd-max77620-Add-DT-binding-details-for-backup-batte.patch.txt (3.62 KB)
0002-mfd-max77620-Add-configurations-of-backup-battery.patch.txt (5.86 KB)


Thanks @ShaneCCC!

Also, would you happen to know if this module is already built into the kernel or could I just insmodit without recompiling the kernel?


I think it’s built into the kernel. And you won’t need patch for next release.

OK. I’ll try to patch and flash. By next release you mean L4T 28.2?

@ShanceCCC. Thanks for your patch. It works for me. :)