SN65LVCP202: SN65LVCP202RGET VBB supply

Nidhi P Shetty

Part Number: SN65LVCP202

Tool/software:

For SN65LVCP202, I see that VBB is receiver input biasing voltage which is typically 1.6V. Also, I see that VBB is shown in internal self-biasing circuit indicating there is VBB present internally.

Could you please help me with below queries.

If VBB is internally generated, then can we leave VBB pin as No connect?
If not, what should be the external voltage, we need to connect to VBB pin
If I use AC coupled LVDS inputs, can I leave VBB as No connect?
If I use AC coupling then DC bias the input lines to say 1.8V, what should be the voltage we need to supply to VBB? What is the expected supply current in this case?

Regards

Nidhi P Shetty

over 1 year ago

0 David Waier over 1 year ago

TI__Mastermind 20901 points

Hi Nidhi,

Thank you for posting your question. Please allow for the relevant engineers to get back to you as soon as possible. Thank you for your patience.

Best,
David

0 Brian Zhou over 1 year ago in reply to David Waier

TI__Guru*** 145215 points

Nidhi P Shetty said:
If VBB is internally generated, then can we leave VBB pin as No connect?

VBB still need t be connected even if AC coupled.

Nidhi P Shetty said:
If not, what should be the external voltage, we need to connect to VBB pin

should be 1,6v

Nidhi P Shetty said:
f I use AC coupled LVDS inputs, can I leave VBB as No connect?

VBB should be conencted for ac coupled

Nidhi P Shetty said:
If I use AC coupling then DC bias the input lines to say 1.8V, what should be the voltage we need to supply to VBB? What is the expected supply current in this case?

VBB should be 1.8v if DC bias the input at 1.8v.

Regards

Brian

0 Nidhi P Shetty over 1 year ago in reply to Brian Zhou

Prodigy 20 points

Brian Zhou said:
it can be no connect if AC coupled.

I have attached my schematics for SN65LVCP202RGET. I have used AC coupling (mounted C12, C13, C14 and C15) in my design.

I have added cross marks in blue to highlight my query

1. As i have used AC coupling can I DNI R49 which disconnects VBB?

2. As I have used AC coupling can I DNI R21, R22, R23, R24, R25, R26, R27 and R28? as I do not need to provide external DC bias when AC coupled?

Brian Zhou said:
should be 1,6v

What is the current requirement for VBB when 1.8V is used as VBB?

0 Brian Zhou over 1 year ago in reply to Nidhi P Shetty

TI__Guru*** 145215 points

for 1: Vbb is needed even if for AC coupled, so R49 is still needed , ( looks I replied wrong last time.)

for 2: you can DNI R13/R14, R21, R22, R23, R24, R25, R26, R27 and R28.

Also remove external bias.

There are two 50ohm inside 1A/1B and biased by VBB, you don't need to bias externally.

Best

Brian

0 Nidhi P Shetty over 1 year ago in reply to Brian Zhou

Prodigy 20 points

Brian Zhou said:
for 1: Vbb is needed even if for AC coupled, so R49 is still needed , ( looks I replied wrong last time.)

What is the acceptable range for VBB? Whether VBB can be 1.8V if I connect SN65LVCP202RGET output to a wide common mode input acceptable device like D9LVRA2DEMRQ1? (My schematics shows 1.8V. But I still thought of double checking with you)

0 Brian Zhou over 1 year ago in reply to Nidhi P Shetty

TI__Guru*** 145215 points

Hi Nidhi:

let me check with designer to make sure.

Best

Brian

0 Nidhi P Shetty over 1 year ago in reply to Brian Zhou

Prodigy 20 points

Sure, will be waiting for your response.

Thanks

0 Brian Zhou over 1 year ago in reply to Nidhi P Shetty

TI__Guru*** 145215 points

Do you know what signal you are going to send? LVDS, LVPCEL, or CML?

Best

Brian

0 Nidhi P Shetty over 1 year ago in reply to Brian Zhou

Prodigy 20 points

We'll be using it as LVDS

0 Brian Zhou over 1 year ago in reply to Nidhi P Shetty

TI__Guru*** 145215 points

For LVDS, common mode biase shoud be 1.2vx.

you can look at this document for more detail.

AC-Coupling Between Differential LVPECL, LVDS, HSTL, and CML.pdf

Best

Brian

0 Nidhi P Shetty over 1 year ago in reply to Brian Zhou

Prodigy 20 points

I understand that LVDS common mode voltage is typically 1.2V as per the standard. But why the SN65LVCP202RGET datasheet states that VBB typical is 1.6V? Is it okay to use 1.2V when minimum VBB value is not specified in the datasheet?

0 Brian Zhou over 1 year ago in reply to Nidhi P Shetty

TI__Guru*** 145215 points

SN65LVCP202 is designed for LVCP, that's why VBB is set for 1.6v.

SInce it's LVDS for your application, then VBB should be 1.2v.

Best

Brian

0 Nidhi P Shetty over 1 year ago in reply to Brian Zhou

Prodigy 20 points

okay

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SN65LVCP202: SN65LVCP202RGET VBB supply