Reg.AM3359 and TPS65910AA1RSL

Ibram sahibu

Other Parts Discussed in Thread: AM3359

Hi,

I am facing some issue in our customzed boards design where we use AM3359 Silicon Rev 2.1 with TPS65910AA1RSL. I have also discussed the following issue with TI rep on the same subject in Sitara forum. I am posting it again here.

VDDS_RTC of AM3359 is getting powered from VRTC(pin29)of PMIC. The board was working fine few days but suddenly PMIC became non functioning. I took the measurement on that pin it is about 1.4V instead of 1.8V. AM3359 is unable to provide PMIC_Power_Enable signal to PMIC.

When I gave 1.8V externally to that pin, It is back to working. So I have following queries:

1. what is the best to solve this problem? I am also aware that external LDO is suggested.

2.How it should be done? do we have to short external LDO output and VRTC output of PMIC together?

please help me clear this doubts.

Regards,

Ibram

over 9 years ago

0 Kevin LaRosa over 9 years ago

TI__Genius 17380 points

The best solution is definitely to add the external LDO to provide the VDDS_RTC to the AM3359. The VRTC pin of the TPS65910AA1RSL is intended for internal use only. In this case you do not need to short the external LDO output and the VRTC output of the PMIC together, just leave the VRTC connected to the cap and connect the LDO output to the VDDS_RTC pin.

Thanks,

Kevin LaRosa

0 Ibram sahibu over 9 years ago in reply to Kevin LaRosa

Intellectual 600 points

Hi Kevin,

If we do like that , will RTC values be retained in the processor as we are using AM3359's RTC.

Regards,

Ibram

0 Ibram sahibu over 9 years ago in reply to Ibram sahibu

Intellectual 600 points

Hi Kevin,

Have you got any updates?

Regards,

Ibram

0 Puneet Sehgal over 9 years ago in reply to Ibram sahibu

TI__Expert 6090 points

As soon as the RTC LDO that powers RTC of the processor is on, this will keep the RTC alive.

So the external LDO has to be always on LDO.

0 Ibram sahibu over 9 years ago in reply to Puneet Sehgal

Intellectual 600 points

Hi,

you mean we have to short both PMIC's RTC LDO and External LDO together?

Regards,

Ibram

0 Puneet Sehgal over 9 years ago in reply to Ibram sahibu

TI__Expert 6090 points

No, I mean to say just add a cap on VRTC on pmic and leave it. Used external LDO and connect it to RTC of processor.

NO connection from PMIC VRTC LDO to any where except a cap.

0 Ibram sahibu over 9 years ago in reply to Puneet Sehgal

Intellectual 600 points

Hi Puneet,

Thanks for your response.

Just wondering how RTC values are retained in the processor? please explain me because battery back up is available only for PMIC.

when board power is off, then input to the External LDO is also OFF.

Regards,

Ibram

0 Puneet Sehgal over 9 years ago in reply to Ibram sahibu

TI__Expert 6090 points

ibram,

Unfortunately i have limited expertise on processor. I'll contact our prcessor expert who can help you from here.

0 kshin over 9 years ago in reply to Ibram sahibu

TI__Genius 16690 points

The RTC information cannot be maintained when the external LDO is turned off. If you need a coin cell battery back feature, I recommend to use the RTC in PMIC.

0 Ibram sahibu over 9 years ago in reply to kshin

Intellectual 600 points

Hi,

I have tested the board by connecting External LDO and it was working fine. Then i read the datasheet of AM3359, I came to know that there is a internal LDO(1.1V) in it and i think that helps to maintain RTC value when the Board is in RTC only mode.

correct me if i am wrong?

Regards,

Ibram

0 kshin over 9 years ago in reply to Ibram sahibu

TI__Genius 16690 points

The internal LDO in RTC power domain is to generate 1.1V core power from 1.8V power supply required for IO in RTC power domain and requires 1.8V +/-5% (1.710 V to 1.890V) power supply as input. So, you still need the external LDO unless you already have the 1.8V +/-5% power supply on your system.

0 Ibram sahibu over 9 years ago in reply to kshin

Intellectual 600 points

Hi,

Sitara forum suggest to use connect External Battery to be connected to external LDO which powers the RTC domain.

Now My question is, do we need External Battery connected to be VBACKUP(Pin27) of PMIC? If not how to handle with that pin?

Regards,

Ibram

0 Puneet Sehgal over 9 years ago in reply to Ibram sahibu

TI__Expert 6090 points

ibram,

Do you want the PMIC RTC to be running when the system is in low power mode ?

0 Ibram sahibu over 9 years ago in reply to Puneet Sehgal

Intellectual 600 points

No, we are not using PMIC RTC.

Regards,

Ibram

0 Puneet Sehgal over 9 years ago in reply to Ibram sahibu

TI__Expert 6090 points

please connect it to VCC5 , if you can not using it.

0 Ibram sahibu over 9 years ago in reply to Puneet Sehgal

Intellectual 600 points

Hi Puneet,

In our design VCC1 to VCC7 shorted and supplied with 5V. Connecting Vbackup(pin27) to VCC5 means we are shorting with other domain also. Is this meant in the previous post?

Regards,

Ibram