DS90UB948-Q1: SPI PINs(SPLK, POCI, PICO PIN) floating

Jingjing Zhao

Prodigy 80 points

Part Number: DS90UB948-Q1

Hello Experts,

In the spc, It was mentioned that If they are unused, tie to an external pulldown, like below:

May I know what's the reason of it? If the design leave them as floating, what will be happened?

Thanks a lot!

over 3 years ago

0 Ryan Fleetham over 3 years ago

TI__Expert 6585 points

Hi Jingjing,

I will check with our team and get back to you by the end of the week.

Sincerely,

Ryan

0 Jingjing Zhao over 3 years ago in reply to Ryan Fleetham

Prodigy 80 points

Hi Ryan,

Thanks a lot. Waiting your further feedback.

0 Ryan Fleetham over 3 years ago in reply to Jingjing Zhao

TI__Expert 6585 points

Hi Jingjing,

We recommend the external pulldown as a best practice. One reason for this is to help prevent a floating voltage on the pin during something like EMC testing where the weak internal pulldown may not be enough. Similarly, the external pulldown can also help prevent an unexpected voltage on the pin from being passed through the back channel depending on the configuration. Please let me know if you have any additional questions.

Sincerely,

Ryan

0 Jingjing Zhao over 3 years ago in reply to Ryan Fleetham

Prodigy 80 points

Hi Ryan,

Due to public holiday, just saw your reply. Thanks of your answer firstly.

I will check the configuration in our design.

One more question in my hands:

Besides unexpected voltage on the pin from being passed through the back channel in worst case, any other influence of DS90UB948(like wrong output of oLDI or I2C and so on..)?

Sincerely

Jingjing

+1 Ryan Fleetham over 3 years ago in reply to Jingjing Zhao

TI__Expert 6585 points

Hi Jingjing,

The impact of not using external pulldowns on the GPIO will be limited to those GPIO pins on the deserializer and any relevant backchannel GPIO on the serializer set up either intentionally or unintentionally. Other functions such as oLDI, I2C, etc. should not be impacted.

Sincerely,

Ryan

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DS90UB948-Q1: SPI PINs(SPLK, POCI, PICO PIN) floating