DP83825I: Power up sequence

Oba

Part Number: DP83825I
Other Parts Discussed in Thread: TL5209, DP83825EVM

Hello,

My customer has a question for power-up sequence of DP83825.
They will use 3.3V for both VDDA3V3 and VDDIO and want to use the same power source.

But the datasheet says “DP83825I needs VDDA3V3 after VDDIO is fully ramped.” On P 94.
From this description, VDDA3V3 and VDDIO can’t be simply tied if VDDIO=3.3V.

But DP83825EVM uses the same power source, TL5209 output, for both VDDA3V3 and VDDIO if internal power supply is used.

Also the below is from the datasheet and the T2 specifies VDDIO to AVDD delay. The MIN is not specified.

Then this is just a confirmation.

If VDDIO = 3.3V, is simply tying VDDA3V3 and VDDIO really NOT accepted?

Regards,

Oba

over 2 years ago

0 David Creger over 2 years ago

TI__Mastermind 21146 points

Hi Oba,

You can assume T2 has a minimum of 0ms. The requirement is that VDDIO must be fully ramped before VDDA3V3 starts.

This is not taken care of on the EVM, which may still work fine, but not ensure the most robustness over time. Please follow the above recommendation for your use case.

Thanks,

David

0 Oba over 2 years ago in reply to David Creger

TI__Genius 16415 points

Hello David,

Thanks for your reply.

OK, I understand that a load switch or somthing must be put on VDDA3V3 rail.
The figure 1 on the datasheet must be like the below (I added a red line to make clear that the start point of "T2" is hte end point of "T1").
Do you agree with it?

I have an additional question for not DP83825, but DP83826.
According to DP83826 datasheet, it seems that VDDA3V3 and 3.3V VDDIO can be simply tied. Is this understanding correct?
Is the power design different between DP83825 and DP83826?

Regards,
Oba

0 David Creger over 2 years ago in reply to Oba

TI__Mastermind 21146 points

Hi Oba,

I agree with the red line in your image, yes.

I will get back to you about your 826 question later this week.

Thanks,

David

0 David Creger over 2 years ago in reply to David Creger

TI__Mastermind 21146 points

Hi Oba,

The supply sequencing requirement was fixed on the DP83826, so it is different than the DP83825, yes.

Thanks,

David

0 Oba over 2 years ago in reply to David Creger

TI__Genius 16415 points

Hello David,

Thanks for your reply.
So VDDA3V3 and 3.3V VDDIO can be simply tied in DP83826. Correct?

Regards,
Oba

+1 David Creger over 2 years ago in reply to Oba

TI__Mastermind 21146 points

Correct.

-David

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DP83825I: Power up sequence