TUSB8020B: Power-Up Timing Requirements of VDD33 and VDD

Dice-K

Part Number: TUSB8020B

Hi support team,

According to section "7.6 Power-Up Timing Requirements", I understand that VDD33 rising after VDD is a timing violation.
"VDD33 stable before VDD stable."

However, according to section "8.3.5 Power-Up and Reset", it says that there is no timing requirement for VDD and VDD33.
"The TUSB8020B does not have specific power sequencing requirements with respect to the VDD or VDD33 power rails."
Does this mean that if the 4 bullet points are met, it's okay for VDD to rise first?

Regards,
Dice-K

over 2 years ago

0 David (ASIC) Liu over 2 years ago

TI__Guru**** 176991 points

Dice-K

Please see this e2e FAQ, https://e2e.ti.com/support/interface-group/interface/f/interface-forum/994526/faq-tusb8041-what-are-the-power-up-and-reset-timing-requirements-for-the-usb-hub/3673793. Does this help answering your question?

Thanks

David

0 Dice-K over 2 years ago in reply to David (ASIC) Liu

Mastermind 7470 points

Hi David,
Thank you for your reply.

Is the following thinking correct?

The order of VDD and VDD33 does not matter as long as 3ms is secured from the rise of both VDD and VDD33 to the rise of GRSTZ.

Best regards,
Dice-K

0 David (ASIC) Liu over 2 years ago in reply to Dice-K

TI__Guru**** 176991 points

Dice-K

The order of VDD and VDD33 does not matter as long as 3ms is secured from the rise of both VDD and VDD33 to the rise of GRSTZ if 3.3V and 1.1V ramp simultaneously (or within us).

Thanks

David

0 Dice-K over 2 years ago in reply to David (ASIC) Liu

Mastermind 7470 points

Hi David,
Thank you for your reply.

Is the following thinking correct?

It's a problem that VDD is faster than VDD33 by more than 1µs.

Best regards,
Dice-K

0 David (ASIC) Liu over 2 years ago in reply to Dice-K

TI__Guru**** 176991 points

Dice-K

Where did you get the 1us timing spec?

Thanks

David

0 Dice-K over 2 years ago in reply to David (ASIC) Liu

Mastermind 7470 points

Hi David,
Thank you for your reply.

From your previous answer.

"(or within us)"

Best regards,
Dice-K

0 David (ASIC) Liu over 2 years ago in reply to Dice-K

TI__Guru**** 176991 points

Dice-K

The datasheet never made the timing particularly clear. To make sure the hub gets proper reset,

If implementing passive reset circuitry, VDD33 must come up before or at the same time as VDD
If implementing active reset circuitry, then power sequence between VDD33 and VDD does not matter

Thanks

David

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TUSB8020B: Power-Up Timing Requirements of VDD33 and VDD