DS90UB947-Q1: There is 31MHz signal during EMC testing.

Lian Wu

Part Number: DS90UB947-Q1
Other Parts Discussed in Thread: DS90UB948-Q1

Dears:

There is infotainment system to have a EMC testing and they found there are a 31MHz signal between DS90UB947-Q1 and DS90UB948-Q1.

I have checked schematic and Layout requirements with customer, I didn't find any issues.

The EMC test standard is Ford standard.

Pls. kindly help to give some advice, thanks!

over 6 years ago

0 Palaniappan Manickam over 6 years ago

TI__Genius 10475 points

Hello,
We received your question and we will need some additional information. The Apps engineer will respond back.

0 Steven(Shenzhen) Shi over 6 years ago in reply to Palaniappan Manickam

TI__Mastermind 30515 points

Lian,
do you have the plot for this EMC test? also, what is the PCLK in this case? or can you have 31M clock source in the system design? thanks.

best regards,
Steven

0 Lian Wu over 6 years ago in reply to Steven(Shenzhen) Shi

Genius 5250 points

Dear Steven:
There is only 124MHz clock from DS90UB947 providing to Sun's 827.
Other information I will check with customer.
Thanks!

Best regards
Luck Wu

0 Lian Wu over 6 years ago in reply to Steven(Shenzhen) Shi

Genius 5250 points

Hi Steven:
We didn't have the plot for the EMC test.
Could you give some advice about it?

0 Steven(Shenzhen) Shi over 6 years ago in reply to Lian Wu

TI__Mastermind 30515 points

Hi, Lian,
1. please help check the board XO and processor's ref. clock? does it have 31MHz freq.?
2. for FPD-Link, please help:
a. 100Ω (±10% total) differential coupled traces (priority)
b. Minimized intra-pair skew (secondary)
c. Small-size (0402 or smaller) AC-coupling capacitors to minimize pad discontinuity
d. For short traces to connector (<50mm): no vias, place signal pair together on surface layer)
e. For longer traces to connector (>50mm): bury trace in inner signal layer
f. 45-degree corners ok, rounded corners best, no asymmetric meanders
g. Continuous ground plane underneath traces to connector
h. Avoid crossing polarity using vias

thanks.

best regard,
Steven

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DS90UB947-Q1: There is 31MHz signal during EMC testing.