SN65CML100: What should be VBB value when termination IC has 3.3 Voltage reference

Atharva U

Intellectual 400 points

Part Number: SN65CML100

Trying to use SN65CML100 in my design.

Using Lattice FPGA to drive true LVDS signals and need to convert them to HDMI physical layer compatible (CML)

On terminal side Chip which converts from HDMI (TMDS) to TTL logic for my RGB display, here is the snapshot of AC specs

I wanted to run through TI experts and understand if my design for SN65CML100 is okay ?

have to not completely understood how to set output CML Voltage bias required by HDMI to TTL IC on SN65CML100

Can you please help ?

over 2 years ago

0 Ikechukwu Anyiam over 2 years ago

TI__Mastermind 35130 points

Hi Atharva,

Vbb should be left unconnected, and the outputs should be terminated with 50-ohm to Vtt as shown in Figure 3 in the datasheet for LVDS to CML translation.

Regards,

I.K.

0 Atharva U over 2 years ago in reply to Ikechukwu Anyiam

Intellectual 400 points

Thanks I.K. for your response.

Understood about VBB supply not being connected.

But 50ohm terminations should ideally available on terminating IC, is my assumption wrong.

In any case, I will have them available on termination if required.

Thanks again

0 David (ASIC) Liu over 2 years ago in reply to Atharva U

TI__Guru*** 139705 points

Hi,

Please check to see if the termination IC has internal 50ohm termination to VTT. If not, then you need to add the external termination.

Thanks

David

0 Atharva U over 2 years ago in reply to David (ASIC) Liu

Intellectual 400 points

Hello,

Little bit confused about one thing.

If all terminations are external to IC, not sure what exactly it is doing apart from making input output independent of DC bias.

Is this chip acting as repeater/redriver of the signal as well ?

Thanks

ATharva

0 Ikechukwu Anyiam over 2 years ago in reply to Atharva U

TI__Mastermind 35130 points

As the outputs are biased by a constant current source, termination is required to generate the differential swing (reference Output Electrical Characteristics table in the datasheet).

Regards,

I.K.

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SN65CML100: What should be VBB value when termination IC has 3.3 Voltage reference