RTC Current consumption in Xavier SOM

Autonomous Machines Jetson & Embedded Systems Jetson AGX Xavier
1

Hello
What is the current consumption on VCC_RTC pin when system is disconnected from power ?
What is the charging voltage in CV mode and charging current in CC mode ?
What is the voltage of PMIC in SOM board ?
Thanks

2

Hi,

Typical Ibbatt = 2.0uA @ 2.45V.

800ÎĽA maximum CC-CV backup battery charger.

2.5V – 3.5V adjustable backup battery setting with ± 3% Tolerance.

3

Hi,

Regarding the super cap.

In Xavier (EVB) schematic Refdes C512 P.N: XH414HG IV01E is rated to 3.3V and your answer is that it could be charged to 3.5V. Also in the “Design guide” p.82 VCC_RTC is defined as 1.65V - 5.5V

How could it be?

does the pmic is a charger or a source to a charger?

Thanks

4

Hi, 2.5V - 3.5V is the charging level range of PMIC. VCC_RTC is the supply to RTC part of Tegra, it can be supplied by backup battery or super cap, and its range is 1.65V - 5.5V.

5

I don’t understand your answer…

what would happed to each capacitors? (charge level, discharge, damage)

a 2V cap
a 3V cap
a 4V cap
a 5V cap

Thanks

6

The cap will be charged to the output charging voltage level you set in PMIC (2.5V - 3.5V).

1 Like
7

Is there a way to configure the PMIC? if so what is it?

8

Have a check the device tree. Modify the status to “okay” and voltage.
./galen/kernel-dts/common/tegra194-spmic-p2888-0001.dtsi

backup-battery {
                                backup-battery-charging-current = <100>;
                                backup-battery-charging-voltage = <3000000>;
                                backup-battery-output-resister = <100>;
                                status = "disabled";
                        };
9

Can VCC_RTC be powered from the same supply as SYS_VIN_MV, or will this conflict with the PMIC on the Xavier SOM?

10

Please do not change any settings in module.

11

The device tree I extracted from my device says “disabled” for backup-battery. I am running the developer board and the super cap is most certainly charging to the 3V default voltage at some controlled rate? So why if this is disabled does it charge the cap? I am looking to maybe swap for a rechargeable battery to get longer runtime from the RTC just want to figure out proper PMIC settings. You mention needing to set “okay” yet it seems to charge whatever is hanging on VCC_RTC?

12

It needs to set to “okay” to enable charging and rechargeable battery/cap can be charged.

13

Hi,
Is there documentation that shows the valid settings for the RTC in the device tree? For each of the below settings, what are the min and max values and what are the units:

backup-battery {
backup-battery-charging-current = <100>;
backup-battery-charging-voltage = <3000000>;
backup-battery-output-resister = <100>;
status = “disabled”;
};
Thanks

14

Also, would a LTC-7PN cell work as a backup battery? It has a max output of 3.6V. Would the voltage be too high or does that fall within the 3% tolerance (not sure if the tolerance was specified as charging voltage or input voltage)?

15

Hi bschulz,

Please open a new topic for your issue. Thanks