LP8733: Power down sequence mismatch with AM64x

Koichiro Tashiro

Part Number: LP8733
Other Parts Discussed in Thread: AM6412, TPS745

Hi,

My customer is using LP873364 for AM6412 power supply as it is recommended solution in below document.
https://www.ti.com/jp/lit/an/slda059/slda059.pdf?ts=1690441858442&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252Fja-jp%252FAM6421%253FkeyMatch%253DAM6421%2526tisearch%253Dsearch-everything%2526usecase%253DGPN

But they found there is power-down sequence mismatch between AM64x and LP873364.

Here is LP873364 power down sequence. All power rails are off simultaneously.
https://www.ti.com/lit/ug/snvu810/snvu810.pdf?ts=1641848546273

On the other hand, AM64x power down sequence requires VDD_CORE needs to be shut of last if VDD_CORE=0.75V.
https://www.ti.com/lit/ds/symlink/am6421.pdf?ts=1690442004964&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252Fja-jp%252FAM6421%253FkeyMatch%253DAM6421%2526tisearch%253Dsearch-everything%2526usecase%253DGPN

Q1) Why there is such mismatch even LP873364 is recommended for AM64x?
Q2) What is consequence if above power-down violation is applied to AM64x?
(device reliability issue, etc.)

Thanks and regards,
Koichiro Tashiro

over 1 year ago

0 James Steenbock over 1 year ago

TI__Mastermind 19860 points

Hi Koichiro,

The gray box indicates that the VDD_CORE signal can go low only at the edges of that window. The dashed line boxes indicate that the signal can go low at any time in that window.

Using this notation, it looks like VDD_CORE can be shut down at the same time as the other rails and still be a valid sequence, which lines up with our LP873364 recommendation.

Regards,

James

0 Koichiro Tashiro over 1 year ago in reply to James Steenbock

TI__Mastermind 22340 points

Hi James,

Please see below note#5 just after Figure 7-6 in AM64x datasheet.
There is timing requirement between VDD_CORE(0.75V) and VDDR_CORE.

VDDR_CORE is supplied from TPS745 and timing is controlled by LP873364 GPO2.
As GPO2 goes low before 0.75V BUCK0(VDD_CORE) shut down, above requirement is always met, correct?

Thanks and regards,
Koichiro Tashiro

+1 James Steenbock over 1 year ago in reply to Koichiro Tashiro

TI__Mastermind 19860 points

Hi Koichiro,

Yes, the requirement specified above would be met by the GPO2 timing shown in the power sequence.

Koichiro Tashiro said:
What is consequence if above power-down violation is applied to AM64x?

This question would best be answered by the AM64x support team. I would recommend asking this specific question in a new thread and tagging the AM64x as the main part.

Regards,

James

0 Koichiro Tashiro over 1 year ago in reply to James Steenbock

TI__Mastermind 22340 points

Hi James,

Thanks I understood.
I will ask the remaining question to AM64x support.

Thanks and regards,
Koichiro Tashiro

Power management

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LP8733: Power down sequence mismatch with AM64x