DS125BR800A: question regarding impedance

Patty Chuang

Part Number: DS125BR800A

Hi Team,

my customer would like to apply DS125BR800ANJYT as SATA re-driver solution on AMD platform.

In the MB design, the MB ( host ) use 85 ohm as target impedance but the SATA impedance is 100 ohm in the spec.

Can customer use difference impedance routing on the driver input and output side? Or do you have better suggestion on this?

85 ohm impedance input and 100 ohm impedance output for SATA TX signals.
100 ohm impedance input and 85 ohm impedance output for SATA RX signals.

Thanks!

Patty Chuang

over 2 years ago

0 Nasser Mohammadi over 2 years ago

TI__Guru* 93670 points

Hi Patty,

We should use the same impedance all the way - either 85-ohm or 100-ohm. Otherwise this impedance difference will cause reflections and affect the overall signal integrity. At minimum, please ask customer to do signal integrity analyses to make sure this impedance mis-match would not cause any negative side effect for SATA specifications.

Regards,Nasser.

0 Oliver Lin over 2 years ago in reply to Nasser Mohammadi

TI__Expert 4475 points

Hi Nasser,

We got another further question, for this device will have mode pin to change mode, if customer change this pin setting, this will cause our device changing impedance from redriver internally? Or this is something no need to be considered?

Because customer might transfer SATA and PCIe signal.

0 Nasser Mohammadi over 2 years ago in reply to Oliver Lin

TI__Guru* 93670 points

Hi Oliver,

Impedance does not change based on Mode pin settings.

Regards,Nasser

0 Oliver Lin over 2 years ago in reply to Nasser Mohammadi

TI__Expert 4475 points

Hi Nasser,

If this is the case, what kind of impedance customer should implement? To fit SATA and PCIe application.

0 Nasser Mohammadi over 2 years ago in reply to Oliver Lin

TI__Guru* 93670 points

Hi Oliver,

This depends on the connectors used. Typically SATA is 100-ohm and PCIe is 85-ohm. If there is no connector or no impedance change, then customer can use 100-ohm for both SATA and PCIe. However, if there is 85-ohm connector then it is recommended to use 85-ohm impedance to match the connector.

Regards,Nasser

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DS125BR800A: question regarding impedance