ADS8664: Regarding the power-up sequence

Masanori Tachibana

Part Number: ADS8664

Hello support team,

I have a question regarding the power-up sequence of ADS8664.

Is there any regulation concerning the sequence at power on?
For example, which of AVDD and DVDD needs to be powered-up first?

Best regards,
M. Tachibana

over 9 years ago

0 ReedKacz over 9 years ago

TI__Expert 3687 points

Hello,

The power up sequence of the ADS8664 is not explicitly defined in the datasheet.

The datasheet references a TI Design that uses another SAR from the same family, TIDA-00164, and in this design the AVDD and DVDD supplies are tied together.

I recommend having AVDD and DVDD come on at the same time to avoid any power sequencing issues.

Please let me know if you have any follow-up questions.

Thanks,

Reed Kaczmarek

0 Masanori Tachibana over 9 years ago in reply to ReedKacz

Genius 5350 points

Hello Kaczmarek-san,

Thank you for your reply.

In case of AVDD = 5 V, DVDD = 3.3 V, AVDD and DVDD can not be connected.
So they can not be powered-up completely at the same time.
In this case, how should it be done?

Best regards,
M. Tachibana

0 ReedKacz over 9 years ago in reply to Masanori Tachibana

TI__Expert 3687 points

Hello,

I would recommend bringing the AVDD up first if having them sequence together is not an option. My reasoning is because the electrical characteristics table shows the DVDD should not exceed AVDD. See image below:

Thank you,

Reed Kaczmarek

0 Masanori Tachibana over 9 years ago in reply to ReedKacz

Genius 5350 points

Hello Kaczmarek-san,

Thank you for your prompt reply.

I understood that AVDD should be powered-up earlier than DVDD.
Thank you for teaching me.
Your advice was very helpful for me.

Best regards,
M. Tachibana

0 Masanori Tachibana over 8 years ago in reply to Masanori Tachibana

Genius 5350 points

Hello Kaczmarek-san,

If DVDD powers up earlier than AVDD, what kind of problems can be considered?
Could you teach me?

Best regards,
M. Tachibana

0 ReedKacz over 8 years ago in reply to Masanori Tachibana

TI__Expert 3687 points

Hello,

Power sequencing is necessary to ensure certain internal circuits are powered up in the proper order. With this device, since the power sequencing is not directly specified in the datasheet, it leads you to believe that it is not overly critical for the ADS8664. By ensuring that AVDD is turned on either simultaneously or before DVDD, then the ADS8664 will operate properly. Some general problems that can be seen due to improper power sequencing are improper internal circuit biasing, improper digital communication, or device improper operation.

Thank you,
Reed

0 Masanori Tachibana over 8 years ago in reply to ReedKacz

Genius 5350 points

Hello Reed-san,

Thank you for your reply.

Could you teach me about the more specific problems when DVDD starts before AVDD?
Aren't they known more concretely since the power on sequence is not overly critical?

Best regards,
M. Tachibana

0 Cynthia over 8 years ago in reply to Masanori Tachibana

TI__Mastermind 25070 points

Hello,

Since this is not a recommended condition, these conditions are not looked at deeply; there is no risk analysis on this.
At worst case, if you are worried about violating this condition during start up, be sure to not run the device until both power supplies have settled.

Regards,
Cynthia

0 Masanori Tachibana over 8 years ago in reply to Cynthia

Genius 5350 points

Hello Cynthia-san,

I understood.
Thanks for your advice.

Best regards,
M. Tachibana

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ADS8664: Regarding the power-up sequence