AM3352 Query regarding RTC time functionality feature

Manoj Agarwal

Other Parts Discussed in Thread: AM3352

We are using "RTC timer functionality but no RTC-only mode" . As per page no 6 of AM335x Schematic Checklist it is written that "any AM335x 1.8 V power supply3" to be used for VDDS_RTC connection. We understand that "any AM335x 1.8 V power supply3" means that we can use external LDO for supply 1.8V power supply to VDDS_RTC connection.

We assume that "any AM335x 1.8 V power supply3" doesn't mean that we need to use 1.8V power supply which is being driven by AM335X 1.8V supply rail.

Please confirm our understanding.

Regards

Manoj A

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Your understanding is wrong. You must use one of the AM335X 1.8V supply rails.

0 Manoj Agarwal over 9 years ago in reply to Biser Gatchev-XID

Expert 1030 points

Hi Biser,

Thanks for your reply.

I checked that starter kit schematic and found that they have used external LDO. I assumed that they are using external LDO because they are using RTC-Only mode. Please let me know if our understanding is correct.

In our case we are using RTC timer functionality so fro this mode we need to used only any AM335x 1.8 V power supply.

0 Biser Gatchev-XID over 9 years ago in reply to Manoj Agarwal

TI__Guru**** 393215 points

Yes, you are correct. The PMIC on the SK cannot provide the necessary current on VRTC in OFF mode, so an external LDO is used. This is only for supporting RTC-only mode.

0 Manoj Agarwal over 9 years ago in reply to Biser Gatchev-XID

Expert 1030 points

Hi Biser Sir,

Please also recommended which 1.8V rail of Am3352 we can connect for VDDS_RTC supply. Is there any criteria for choosing the 1.8V supply rail.

0 Biser Gatchev-XID over 9 years ago in reply to Manoj Agarwal

TI__Guru**** 393215 points

No, you can use any 1.8V rail which can support the additional load of VDDS_RTC.

0 Manoj Agarwal over 9 years ago in reply to Biser Gatchev-XID

Expert 1030 points

Hi,

Please refer attached Reset scheme for RTC timer functionality. Please check is these connection are ok for RTC timer functionality. We are using 1.8V(VDDS_RTC : VAUX1) supply. Please let me know if there is any timing requirement for RTC_PWRONRST* signals after VDDS_RTC supply. As we see in datasheet it is written 1ms when internal RTC LDO is enabled but in RTC time functionality Internal RTC LOD is disabled. So is there any timing requirement for RTC_PWRONRST* to be low until VDDS_RTC or VDD_CORE supply is up.

0 Biser Gatchev-XID over 9 years ago in reply to Manoj Agarwal

TI__Guru**** 393215 points

I can't see any attachments.

0 Manoj Agarwal over 9 years ago in reply to Biser Gatchev-XID

Expert 1030 points

Reset Scheme

0 Biser Gatchev-XID over 9 years ago in reply to Manoj Agarwal

TI__Guru**** 393215 points

You can remove the capacitor on RTC_PWRONRSTN. The open-drain buffer on WARMRSTN is unnecessary and should also be removed. Pullup resistor on WARMRSTN must be connected to the same power rail as VDDSHV6.

0 Manoj Agarwal over 9 years ago in reply to Biser Gatchev-XID

Expert 1030 points

Hi Biser Sir,

Thanks for reply. I will remove capacitor on RTC_PWRONRSTN. Regading Opendrain buffer on WARMRSTN , on power
up the nRESETOUT signal on the processor may go high, causing the SYS_RESETn signal to go HI before it should. This change reenforces the reset with the PORZn reset. This recommendation is written from beagleboard change list.

0 Biser Gatchev-XID over 9 years ago in reply to Manoj Agarwal

TI__Guru**** 393215 points

OK, I agree.

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AM3352 Query regarding RTC time functionality feature