DS90UB954-Q1: How to select AC coupling capacitor

Tomoaki Yoshida91

Genius 5255 points

Part Number: DS90UB954-Q1

Hi team,

I have a question for AC coupling capacitor.

I will select the AC coupling capacitor with reference to the data sheet table. 228 Design Parameters.

In addition, 8.2.2 Detailed Design Procedure has the following description.

"For 2G operation or back channel frequency of ≤ 10 Mbps, the higher value AC-coupling capacitors 100 nF /47 nF are recommended."

In other words, does it mean that a small capacitor of 33 nF is recommended for fast communication at 4 Gbps?

We are considering the following usecase:

The forward channel datarate of 4Gbps and back channel frequency of 50Mbps

In this case, should we choose 33 nF / 15 nF?

Best regards,

Tomoaki Yoshida

over 7 years ago

0 Charley Cai over 7 years ago

TI__Genius 12866 points

The forward channel datarate of 4Gbps and back channel frequency of 50Mbps
Yes, in this case you shoud choose 33nF/ 15nF.

Best Regards,
Charley Cai

0 Tomoaki Yoshida91 over 7 years ago in reply to Charley Cai

Genius 5255 points

Hi Charley-san,

Tnank you for your support.

I have an additional question.

In the case of FC 4 Gbps and BC 50 Mbps, must it be an AC coupling capacitor of 100 nF / 47 nF?

I think that because the capacitor is large, the band width is insufficient and the Eye quality deteriorates.

In order to ensure communication quality, it should be 33 nF / 15 nF, but I think that communication can be made according to conditions even at 100 nF / 47 nF.

Is this recognition correct?

Best reagrad,

Tomoaki Yoshida

0 Charley Cai over 7 years ago in reply to Tomoaki Yoshida91

TI__Genius 12866 points

Yes, the device can functional with 100nF/47nF. The deterioration is not significant.

Best Regards,
Charley Cai

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DS90UB954-Q1: How to select AC coupling capacitor