AM3359 Built in RTC Operation from Coin Cell

Paul Joseph

Other Parts Discussed in Thread: BQ32000, TPS65910, TPS65910A

Can you advise if there is an option to run the RTC from a seperate coin cell whne main power is off and therefore retain the date/time.

From the errata, Advisory 1.0.5 regarding clock gating I am not sure if this is possible, please advise if the RTC/Coin cell combination is possible or if an external PMU with an integrated RTC is required. Thank you.

over 14 years ago

0 *** Liu over 14 years ago

Prodigy 140 points

Maybe you can use TPS65910 or external RTC IC like BQ32000.

0 *** Liu over 14 years ago

Prodigy 140 points

see below:

http://e2e.ti.com/support/power_management/pmu/f/200/p/166378/683702.aspx#683702

0 kshin over 14 years ago

TI__Genius 16690 points

AM335x RTC information cannot be maintained in the RTC-only mode (only RTC power domain is active and the rest of power supplies are turned off) with ES1.0 silicon due to the silicon issue described in the advisory 1.0.5.

These can be options after the issue is fixed in ES2.0.

Option1: Coin cell + 1.8 V output LDO

AM335x RTC power supply VDDS_RTC (1.8V) can be powered by external 1.8 V output LDO powered by coin cell. The external LDO is required for providing regulated 1.8 V throughout coin cell battery lifetime.

Option2: Supercap + 1.8V output LDO

AM335x RTC power supply VDDS_RTC (1.8V) can be powered by external 1.8 V output LDO powered by supercap. The external LDO is required for providing regulated 1.8 V. The supercap can be charged while power source is available.

Option3: PMIC with coin cell/supercap backup feature

PMIC switches the power source for RTC power supply from main battery to coin cell or supercap when main battery power is not available. This will make coin cell battery lifetime longer if coin cell is used for the backup battery. TPS65910A has this feature.

0 Yegor Yefremov over 13 years ago in reply to kshin

Expert 2380 points

Where can I find a driver for tps65910a RTC?

So far I was trying to get some values via i2c-tools, but the stuff I write won't be taken and can't see RTC working:

i2cset -y -f -m 0x21 1 0x2d 0x10 0x21 b

i2cget -f -y 1 0x2d 0x10 b -- always gives 0

Any idea?

0 Michael Williamson over 13 years ago in reply to Yegor Yefremov

Expert 2005 points

The TPS65910A settings appear to disable the RTC (See the extra user guide for the OMAP3 EEPROM settings) by default.

You need to take the PMIC out of power down mode using

i2cset -f -y 1 0x2d 0x3F 0x30 b

That will startup the PMIC RTC circuitry (the defaults for the "A" version of the part are 0x70 for DEVCTRL_REG, and you can't appear to modify the key ones....

-Mike

0 Yegor Yefremov over 13 years ago in reply to Michael Williamson

Expert 2380 points

Thanks for the answer. I got it running and now have another problem: http://e2e.ti.com/support/dsp/sitara_arm174_microprocessors/f/791/t/225987.aspx. Could you please sched light on this?

Yegor

0 reto hermann over 13 years ago in reply to kshin

Intellectual 740 points

Hi,

is there any information about the current consumption (VDDS_RTC supply) of the AM335x processsor (silicon rev. 2.0) when it is operated in RTC only mode? I'm trying to calculate the battery lifetime for the configuration that you have suggested in your post (external LDO).

Best regards

Reto

0 Biser Gatchev-XID over 13 years ago in reply to reto hermann

TI__Guru**** 393215 points

Hi Reto,

Not yet.

Please in the future try to post your questions on new threads. Otherwise they may be easily be overlooked by forum support personnel (mistaken as answers to other people's questions).

Processors

Processors forum

AM3359 Built in RTC Operation from Coin Cell