AM335X RTC on backup battery

Jonathan Bouchard

Other Parts Discussed in Thread: TPS65910A

Hi,

I'm using an AM335X processor and PMIC TPS65217C on a design that requires no battery power except for the RTC that needs to keep working. I have noticed that the only power consumption indication about the RTC is the pin maximum current, which is 5mA. Is there a way to make the RTC work with less than 5mA when all other power are in shutdown mode? I would like to have the RTC on a backup battery/cap/super-cap working for more than a month.

Best regards,

Jonathan

over 12 years ago

0 Biser Gatchev-XID over 12 years ago

TI__Guru**** 393215 points

Hi Jonathan,

First of all, have you read AM335X Errata Advisory 1.0.5? For the current revision the processor RTC will not work correctly if only VDDS_RTC power is present. If possible use an external RTC or change the PMIC to TPS65910A.

Best Regards

Biser

0 Jonathan Bouchard over 12 years ago in reply to Biser Gatchev-XID

Prodigy 160 points

I have read the Errata and noticed this problem.

I would appreciate being able to power in RTC only mode with a super cap or a coin cell on the battery input of the PMIC (with the next silicon revision). I cannot use any other PMIC since I need the Wled boost and DDR3 support. Is there a way I can do this with the TPS65217C without a lithium+ battery? If so, I would like to have a current estimate of the RTC input (in the next revision) so I can calculate the value of the coin cell / super cap on the BAT input of the PMIC.

I'd like to be able to remove (DNI) the external RTC for the next rev of processor.

Best regards,

Jonathan

0 Biser Gatchev-XID over 12 years ago in reply to Jonathan Bouchard

TI__Guru**** 393215 points

Hi Jonathan,

It's way too early to have any information about parameters of Rev.2.0. They will be available only after the device has been verified. As for the 5mA current on VDDS_RTC, this is worst-case maximum. Typical VDDS_RTC currents are 0.3 - 0.4mA (http://processors.wiki.ti.com/index.php/AM335x_Power_Consumption_Summary).

Best Regards

Biser

0 Matthias Fuchs over 12 years ago in reply to Biser Gatchev-XID

Prodigy 170 points

Hi,

in the meantime, do you have any update on the VDDS_RTC current for the new chip rev? I was not sure about the current mentioned in your previous post.

Do we have 5mA with the initial revision and 0.3-0.4mA with the new? That would not be acceptable for a system that needs to keep the date/time for a couple of years.

Matthias

0 Biser Gatchev-XID over 12 years ago in reply to Matthias Fuchs

TI__Guru**** 393215 points

HI Matthias,

Not yet, the Rev.2.0 is under evaluation at the moment. The documents will be updated once this is completed. All currents mentioned above are for Rev.1.0.

0 Sebastian Pfeiffer over 12 years ago in reply to Biser Gatchev-XID

Prodigy 70 points

Hi,

i can not find any information of the AM3352A (Rev.2) RTC power consumption!

Is the REV2 to be always under evaluation?

ciao

Sebastian

0 ATULKUMAR SINGH over 12 years ago in reply to Sebastian Pfeiffer

Prodigy 140 points

Hi,

Please let me know whether the rev 2 has been released for production or not?

If it has been released then what has been added more to it as compared to rev 1 for RTC.

Thanks and regards,

ATUL KUMAR SINGH

0 Biser Gatchev-XID over 12 years ago in reply to ATULKUMAR SINGH

TI__Guru**** 393215 points

Yes, Rev.2.1 is in production now. You can see the differences from Rev.1.0 in the latest Errata document (Rev.E).

0 ATULKUMAR SINGH over 12 years ago in reply to Biser Gatchev-XID

Prodigy 140 points

Hi Biser,

Thanks for your reply.

Please let me know what about the VBACKUP pin of TPS65910A, do i need to connect the coin battery as a backup source.

So as the RTC to function properly when the system is turned off.

Also how to prevent the VDD_CORE not to get turned off for RTC to function properly.

Thanks and regards,

ATUL KUMAR SINGH

0 Biser Gatchev-XID over 12 years ago in reply to ATULKUMAR SINGH

TI__Guru**** 393215 points

the backup battery on VBACKUP provides power to the VRTC LDO when main power is disconnected. Note that VBACKUP has a battery charging function. The AM335X Rev.2.X does not need VDD_CORE to be present for the RTC to function properly.

0 ATULKUMAR SINGH over 12 years ago in reply to Biser Gatchev-XID

Prodigy 140 points

Hi Biser,

Thanks for your reply.

But my doubt was does we need battery on VBACKUP when the system is turned off for RTC to work properly.

Thanks and regards,

ATUL KUMAR SINGH

0 Biser Gatchev-XID over 12 years ago in reply to ATULKUMAR SINGH

TI__Guru**** 393215 points

If only the PMIC is turned off, but main power is present at the VCC7 input, the RTC LDO will be powered from it, and not from the VBACKUP source. Take some time and read the TPS65910A datasheet. If you have further questions about this PMIC, there is a dedicated forum for it: http://e2e.ti.com/support/power_management/pmu/f/43.aspx

0 ATULKUMAR SINGH over 12 years ago in reply to Biser Gatchev-XID

Prodigy 140 points

Hi Biser,

Thanks for your help.

0 Hannes Petermaier over 11 years ago in reply to ATULKUMAR SINGH

Prodigy 235 points

Hello guys,

the question about the current consumption in silicon rev. 2.0 upwards is not clarified yet, are there any news about this?

best regards,

Hannes

0 Biser Gatchev-XID over 11 years ago in reply to Hannes Petermaier

TI__Guru**** 393215 points

Already replied to your other post.

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AM335X RTC on backup battery