AM335x with TPS65910

Daisuke Maeda

Guru 19835 points

Other Parts Discussed in Thread: TPS65910A, TPS65910, AM3354

AM335x VDDS_RTC power is supplied from TPS65910A31 VRTC.
When AM335x is RTC-Only mode, TPS65910A31 is Back-up mode.
Is TPS65910A31 available in this case?

For TPS65910A and TPS65910A3, VRTC power mode in OFF state is Low power mode.
Is not their VRTC available for AM335x VDDS_RTC?
If it is not available, what is the reason?
Does it have a problem that VRTC power mode in OFF state is Low power mode?

Best regards,

Daisuke

over 11 years ago

0 Biser Gatchev-XID over 11 years ago

TI__Guru**** 393215 points

Hi Daisuke,

If you check the TPS65910A User Guide (http://www.ti.com/lit/ug/swcu093b/swcu093b.pdf) Table 1, Figure 1 and Figure 2, you will see from the TPS65910A and TPS65910A3 connection diagram shows an external regulator that should supply VDDS_RTC in OFF mode. This is because the VRTC LDO low-power mode provides less than 0.1mA, which isn't enough for the AM335X VDDS_RTC supply. This external regulator can be an LDO, it doesn't have to be a Buck regulator.

On the other hand, TPS65910A31 in OFF mode provides VRTC LDO full-power of 20mA and can supply directly VDDS_RTC.

Best Regards

Biser

0 Daisuke Maeda over 11 years ago in reply to Biser Gatchev-XID

Guru 19835 points

Hi Biser,

Thank you for your reply.

Biser Gatchev-XID said:

On the other hand, TPS65910A31 in OFF mode provides VRTC LDO full-power of 20mA and can supply directly VDDS_RTC.

In above case, can TPS65910A31 in Backup state supply VDDS_RTC when Am335x is RTC-Only mode?

Best regards,

Daisuke

0 Biser Gatchev-XID over 11 years ago in reply to Daisuke Maeda

TI__Guru**** 393215 points

Hi Daisuke,

Yes, it can.

Best Regards

Biser

0 Daisuke Maeda over 11 years ago in reply to Biser Gatchev-XID

Guru 19835 points

Hi Biser,

Thank you for your reply.

I recommend that AM335x is used with TPS65910A31 to our customer.

Best regards,

Daisuke

0 Daisuke Maeda over 11 years ago in reply to Biser Gatchev-XID

Guru 19835 points

Hi Biser,

When TPS65910A31 is Back-up mode, VRTC LDO is 0.1 mA (IOUTmax).
Is this enough for the AM335X VDDS_RTC supply?

http://www.ti.com/lit/ds/symlink/tps65910a3.pdf
VRTC LDO (Page 12)

A digital clock source can be provided on OSC1_IN
Is TPS65910A31 CLK32KOUT available for RTC_XTALIN (OSC1_IN), if an accurate clock is not needed by the system?

http://processors.wiki.ti.com/index.php/AM335x_Schematic_Checklist#If_RTC_internal_oscillator_is_not_used...

Best regards,

Daisuke

0 Biser Gatchev-XID over 11 years ago in reply to Daisuke Maeda

TI__Guru**** 393215 points

Hi Daisuke,

No, 0.1mA is not enough for VDDS_RTC supply.

Typical consumption values for VDDS_RTC are 0.3 - 0.4mA (http://processors.wiki.ti.com/index.php/AM335x_Power_Consumption_Summary), with worst-case maximum of 5mA (AM335X Datasheet).

However please note that when TPS65910A31 is in Back-up mode, VRTC LDO is in Full power mode.

When TPS65910A or TPS65910A3 is in Back-up mode, VRTC LDO is in Low power mode. That's why an external LDO providing VDDS_RTC has to be used in designs with TPS65910A or TPS65910A3.

For 32kHz clock please check the 32-kHz RTC CLOCK section of DETAILED DESCRIPTION in the TPS65910A datasheet. In summary - you are correct.

Don't forget to take into consideration also AM335X Errata Advisory 1.0.5.

Best Regards

Biser

0 Daisuke Maeda over 11 years ago in reply to Biser Gatchev-XID

Guru 19835 points

Hi Biser,

Thank you for your reply.

When TPS65910A31 is in Backup state, the VRTC regulator is in backup mode which is 0.1 mA.

http://www.ti.com/lit/ds/symlink/tps65910a3.pdf
STATE-MACHINE (Page 41)

Is this enough for the AM335X VDDS_RTC supply?
Only when AM335x is in RTC-Only mode, can it supply AM335X VDDS_RTC?

Biser Gatchev-XID said:

Don't forget to take into consideration also AM335X Errata Advisory 1.0.5.

Our customer may use TPS65910A31 Built-in RTC.

http://e2e.ti.com/support/power_management/pmu/f/43/t/224114.aspx

Best regards,

Daisuke

0 Biser Gatchev-XID over 11 years ago in reply to Daisuke Maeda

TI__Guru**** 393215 points

Hi Daisuke,

According to the TPS65910A User Guide, Table 1 ( 7220.tps65910a user guide.pdf) VRTC LDO is in full power mode when TPS65910A31 is in OFF mode.

Best Regards

Biser

0 Daisuke Maeda over 11 years ago in reply to Biser Gatchev-XID

Guru 19835 points

Hi Biser,

Thank you for your reply.

Backup state is not OFF state.
For Backup state please check the section below in the TPS65910 datasheet.

http://www.ti.com/lit/ds/symlink/tps65910a3.pdf
STATE-MACHINE (Page 41)

Best regards,

Daisuke

0 Biser Gatchev-XID over 11 years ago in reply to Daisuke Maeda

TI__Guru**** 393215 points

Hi Daisuke,

I understand what you mean. In this case VRTC LDO will not have enough power to supply the AM335X VDDS_RTC. An external 1.8V LDO should be used for VDDS_RTC.

Best Regards

Biser

0 Daisuke Maeda over 11 years ago in reply to Biser Gatchev-XID

Guru 19835 points

Hi Biser,

Thank you for your reply.

I understood that TPS65910A31 VRTC LDO Back-up mode is not available for AM335x RTC-Only mode.

Best regards,

Daisuke

0 Daisuke Maeda over 11 years ago in reply to Biser Gatchev-XID

Guru 19835 points

Hi Biser,

If AM335x RTC is not used, when TPS65910A31 VRTC LDO is in Back-up mode, can it supply AM335X VDDS_RTC?

Because our customer may use TPS65910A31 Built-in RTC.

Best regards,

Daisuke

0 Biser Gatchev-XID over 11 years ago in reply to Daisuke Maeda

TI__Guru**** 393215 points

Hi Daisuke,

VRTC LDO in Back-up mode provides only up to 0.1mA. VDDS_RTC typical consumption is 0.3 - 0.4mA. Whether the AM335x RTC is used or not, I don't know if VDDS_RTC consumption will get so low, that 0.1mA from VRTC LDO will be enough to supply it.

Best Regards

Biser

0 Daisuke Maeda over 11 years ago in reply to Biser Gatchev-XID

Guru 19835 points

Hi Biser,

Thank you for your reply.

I understand that VRTC LDO in the backup mode is not available to supply AM335X VDDS_RTC.

Best regards,

Daisuke

0 Vishy Canadam over 11 years ago in reply to Daisuke Maeda

Prodigy 140 points

Hi Biser,

I have a question related to this topic.

We will be using AM3354 with TPS65910A3. We will be using the RTC functionality of AM3354 when the system is fully powered. We don't need backup functionality at all (on AM3354 or TPS65910A3).

1) Can I connect VRTC from TPS65910A3 to VDDS_RTC pin of AM3354 ? (and not use an external LDO)

2) Can I leave the VBACKUP pin on TPS65910A3 unconnected ?

3) Can I leave the RTC_XTALIN, RTC_XTALOUT, and VSS_RTC pins on AM3354 unconnected (or tied to GND) ? (no 32K xtal...we can use the internal RC osc instead)

Best regards

Vishy

0 peaves over 11 years ago in reply to Vishy Canadam

TI__Guru 55265 points

I'm not the best person to answer your questions related to TPS65910A3, but wanted to discuss your plans to use the AM335x RTC without an external crystal.

Do you realize the internal RC32K oscillator does not provide an accurate clock output frequency? This RC based clock source varies over the range of 16KHz to 60KHz.

Regards,
Paul

0 Vishy Canadam over 11 years ago in reply to peaves

Prodigy 140 points

Thanks Paul. I do know that the RC32K is not accurate and we are ok with that. AM3354 is not our main processor in the design. In any case, I will leave the external OSC as a stuffing option.

Thanks

Vishy

PS : I hope somebody gets back to me on the other questions.

0 Biser Gatchev-XID over 11 years ago in reply to Vishy Canadam

TI__Guru**** 393215 points

Hi Vishy,

Vishy Canadam said:

1) Can I connect VRTC from TPS65910A3 to VDDS_RTC pin of AM3354 ? (and not use an external LDO)

2) Can I leave the VBACKUP pin on TPS65910A3 unconnected ?

I understand from your post that you don't plan to implement low-power modes. If this is true the answer to both questions above is "yes".

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