AM3352: RTC stops on power-off

When RTC_XTALIN is probed during poweroff.
It shifts to HIGH once the board is powered off.
Similarly RTC_XTALOUT is going LOW when board is poweredoff.

I need information how the coin cell is connected.

Biser Gatchev-XID said:

Please describe in detail how this is connected.

1.8V from Coincell is given to VDDS_RTC (D7 on ZCZ)

Hence, I can see that VDDS_RTC is having 1.8V when the board is poweredoff or the main supply of board is removed.

Yes, the voltage is stabilized with TPS70918.

3.3V Coincell -> TPS70918 -> 1.8V to VDDS_RTC

Biser Gatchev-XID said:

What you expect is called RTC-only mode. Please check that you have the right connections: http://www.ti.com/lit/an/sprabn2/sprabn2.pdf section 2.14.

&tps {  /delete-property/ ti,pmic-shutdown-controller;  }

&rtc {
        system-power-controller;
        clocks = <&clk_32768_ck>, <&clkdiv32k_ick>;
        clock-names = "ext-clk", "int-clk";
};

or am I missing something over here?

Check the hardware connections first. See Table 2 for reference. Also check the RTC reset signal on your board.

Sure, I'll check that and get back to you.

Thanks for you quick responses.

Biser,

We use a bit different hardware configuration as compared to the one that is mentioned in the documents provided.

We use TPS65217D (RTC Only mode is not supported, as per the document), we use a Primary PMIC (regulate i/p voltage to get a fixed o/p of 5V) to control the power supplied to Secondary PMIC (TPS65217D). Hence, when we poweroff the device, we cut the complete supply of TPS65217D through gpio-poweroff. Therefore, the supply to RTC module inside the Processor is cut. Thus, RTC doesn't work on poweroff.

Now the point is, we have connected the Coincell in such a way that the VDDS_RTC stays at 1.8V even when the processor is completely powered off, I believe that this is not sufficient enough to make the RTC block of the Processor work. Can you kindly let me know, what am I missing here ?

Also, as per my understanding the RTC block of the Processor (AM3352) gets power supply from LDO1 of TPS65217D, in that case, can I directly bypass the power supply of RTC block to use my external Power supply from Coincell (Regulated 1.8V) instead of LDO1.

Biser Gatchev-XID said:

Check the RTC reset signal on your board. If it's low in power-off, the RTC will not work.

Thank you so much for your quick responses, I'd ensure the RTC Reset to be HIGH (1.8V) and give you an update.

Thanks again for the information.

Biser,

By ensuring that RTC Reset stays HIGH when the board is poweredoff, RTC works in principle.

I'd like to know, if there would be any drawbacks by always supplying 1.8V to RTC Reset. As it was mentioned in the data sheet that, RTC_PWRONRSTn should be asserted for at least 1 ms to provide enough time for the internal RTC LDO output to reach a valid level before RTC reset is released.

Since, we don't use LDO1, would that statement be applicable in our use case ?

Thanks for your patience and support.