SN75DP130: TDR of SN75DP130 EVM Failing 100 Ohm +/-10%

1859464

Part Number: SN75DP130

TDR of SN75DP130 EVM shows impedance high of 106.7 Ohm and low at 74.3 Ohm, exceeding 100 Ohm +/-10%. The low of 74.3 Ohm occurs at the SN75DP130. TDR was measured on SN75DP130 EVM output side with TDR filter risetime set to 130ps. Is this the expected impedance profile of SN75DP130 package/die ? Please refer to TDR plot in attached PDF. TDR_SN75DP130_EVM_v0.pdf

Regards,

over 5 years ago

0 JMMN over 5 years ago

TI__Guru 60865 points

Hi KT,

Can you provide schematic / layout of the area included in the TDR?

Thanks,
JMMN

0 1859464 over 5 years ago in reply to JMMN

Intellectual 575 points

Hi JMMN,

The board is TI SN75DP130 EVM. See attached PDF for snapshot of section of EVM that TDR was done on.

a. Do you need me to provide further info on schematic and layout section of TI SN75DP130 EVM ?

b. If you like, I can provide TDR of just SMA cables and test fixture so you can more easily see where TI EVM starts in TDR plot.

Regards,
KT

TI_DP130_EVM_TDR.pdf

0 JMMN over 5 years ago in reply to 1859464

TI__Guru 60865 points

Ah, I didn't see that it was on our EVM. Let me try to locate one in the lab and run TDR on it.

Thanks,
JMMN

0 1859464 over 5 years ago in reply to JMMN

Intellectual 575 points

Hi JMMN,

Were you able to replicate my TDR measurement ?

Regards,

0 JMMN over 5 years ago in reply to JMMN

TI__Guru 60865 points

KT,

Yes, it looks like the pin capacitance is causing a low side excursion in the TDR. This is an older device, so I will need to trace the history and see if I can find any more information on what platform the original compliance test was done on. The pad size / layout of this EVM may be impacting the results.

Regards,
JMMN

0 1859464 over 5 years ago in reply to JMMN

Intellectual 575 points

Hi JMMN,
On our product board with the DP130, when the TDR with DP130 populated is compared to TDR with DP130 not populated, the large capacitive low-side excursion is only there when DP130 is populated.
Regards,
KT

0 JMMN over 5 years ago in reply to 1859464

TI__Guru 60865 points

KT,

Your results match the results I am seeing in my lab where there is a low impedance point at the pin. I have not been able to locate the original TDR data that was taken on the device, but this appears to be the expected performance.

Regards,
JMMN

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SN75DP130: TDR of SN75DP130 EVM Failing 100 Ohm +/-10%