DS90UB925Q-Q1: EMI Issue

Jim CHEN

Expert 4795 points

Part Number: DS90UB925Q-Q1

Dear Team,

My customer met an EMI issue on DS90UB925. This affect their GPS function.

So far they would like to know if they can add 39pF cap on DOUT+/- as below figure to solve this problem.

Please help to confirm. Thanks.

over 8 years ago

0 Palaniappan Manickam over 8 years ago

TI__Genius 10475 points

Hello,
What standard are they trying to meet - is this radiation or immunity test? What is their PCLK freq? Do you have measurement data to show what freq band is this seen at?
These are some general EMI/EMC guidelines that can prove to be helpful resources for your customer:
www.ti.com/.../snaa204.pdf
www.ti.com/.../snaa205.pdf
www.ti.com/.../slyt719.pdf

0 Jim CHEN over 8 years ago in reply to Palaniappan Manickam

TI__Expert 4795 points

Hi Palaniappan,

This is for immunity test. So far FPDlink interferes their GPS signal, and GPS's frequency is at about 1.5GHz.
I am trying to get the PCLK freq information from the customer.
Could you tell me how calculate the frequency of FPDlink signal?

0 Steven(Shenzhen) Shi over 8 years ago in reply to Jim CHEN

TI__Mastermind 30515 points

Jim,
Definitely, the filtering capacitor 39pf is helpful to reduce the EMI. To resolve this EMI issue, TI would recommend to optimize the diff. signals layout and grounding to mitigate the EM inference. as one drawback for this filtering capacitor, the high speed SI would be impacted. If you can't optimize the layout, can you try smaller capacitor (such as 10pf) in this application to balance the SI impact?

best regards,
Steven

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DS90UB925Q-Q1: EMI Issue