SN65LVDT101: LVDS to LVPECL question and recommendation

Tom Schultz

Part Number: SN65LVDT101
Other Parts Discussed in Thread: SN65LVCP23

Team,

My customer has a question.

We are searching for a way to translate a 125Mbps LVDS differential signal from a POF (plastic optical fiber) transceiver (500-900mV differential output), to a LVPECL PHY input (800mV differential input minimum). These voltage ranges align with the below definitions of LVDS/LVPECL from TI’s app note. Note these are defined as single-ended.

We are interested in TI’s SN65LVDx series of parts. However, I’m confused by the voltage ranges presented in the datasheet. I might be misunderstanding single ended vs. differential, etc. Why would a part claiming to have LVPECL output, give only up to 750mV differential output?

Can you shed some light for us?

Thanks,

Tom

over 2 years ago

0 Malik Barton57 over 2 years ago

TI__Guru 64326 points

Hi Tom,

The app note mentioned shows a typical voltage swing for LVPECL. SN65LVDT101 is still outputs a valid LVPECL signal just with a lover overall swing. The key is to make sure the LVPECL receiver is compatible with the the output voltage swing from SN65LVDT101.

0 Tom Schultz over 2 years ago

TI__Expert 3945 points

Hi Malik,

From customer:

"This answer tells me that this part isn’t going to work in our application. Our LVPECL receiver requires a minimum input voltage swing of 800mVpp differential, whereas the SN65LVDT101 specifies it will output 750mVpp max.

Is there any other part you or the team can recommend for this level-shifting LVDS-LVPECL translation?"

0 Malik Barton57 over 2 years ago in reply to Tom Schultz

TI__Guru 64326 points

We have SN65LVCP23 but this device may not fit nicely in the existing customer design if only one channel is used. This is a two channel device.

0 Tom Schultz over 2 years ago in reply to Malik Barton57

TI__Expert 3945 points

Hi Malik,

The customer feels they need a higher voltage swing than what you have offered with this part… I’m afraid the min value for V_OD is still too low. The ENET PHY has a V_IDIFF of 800mVpp min. The signal they need to translate has a 500mV to 900mV Diff Output Voltage (pk-pk). I sent you a separate email with datasheet snippets for the requirements.

Please let me know if there is any TI solution which can solve this problem.

Thanks,

Tom

0 Malik Barton57 over 2 years ago in reply to Tom Schultz

TI__Guru 64326 points

Hi Tom,

I will respond in email.

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

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SN65LVDT101: LVDS to LVPECL question and recommendation