Question about TSB81BA3D TPA and TPB Voltage output levels

Mitchell Kary

Other Parts Discussed in Thread: SN65CML100

Hello,

The data sheet for the TSB81BA3D indicates a VOD output level for TPA and TPB of 265mV max into 56 ohms.

I actually measure a VOD on both TPA and TPB of about 740mV pk-pk when I have an active 1394B S800 connection between two TSB81BA3D ports. I am working on a design where I want to interface the TPB pins to an optical transceiver whose minimum differential voltage requirement is 400mV.

Based on my measurements, I should be ok, but based on the repeater data sheet I would probably want to use a (SN65CML100) buffer to the optical part.

Can you please advise me on the VOD output levels?

Thanks,

Mitch

I have a design for a 1394B optical repeater using the TSB8BA3D with the TPB +/- pins terminated as shown in the data sheet driving the Tx pins of the AC coupled 100 ohm terminated optical transceiver.

over 10 years ago

0 Elias Villegas M. over 10 years ago

TI__Guru* 76130 points

Hello,

I've just looked at the datasheet and it specifies VOD= 700mV TYP.

Where are you seeing 265mV?

Also note that the TSB81BA3D is not recommended for new designs, we recommend the TBS81BA3E

Regards.

0 Mitchell Kary over 10 years ago in reply to Elias Villegas M.

Intellectual 630 points

Elias,

Its funny because I had always thought it was 700mV, but for some reason, I was checking a few things on my design and looked at the section below and didn't see the other reference to VOD earlier in the specification.

One other question for you:

I am interfacing TPB to a fiber module that is AC coupled and has a 100 ohm termination across its TX+/- pins. I was planning on changing the TI recommended termination network for TPB port to use 49.9 ohm instead of 56 ohm. Do you agree with that change?

Thanks.

Mitch

0 Mitchell Kary over 10 years ago in reply to Mitchell Kary

Intellectual 630 points

On the previous post, my paste of the specification excerpt didn't go through.

The section with the VOD of 265mV was on page 14 of specification SLLS783A.

0 Elias Villegas M. over 10 years ago in reply to Mitchell Kary

TI__Guru* 76130 points

Hello,

You can use 49.9 ohm.

Regards.

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Question about TSB81BA3D TPA and TPB Voltage output levels