DS90CR485 PRE-pin pull-up voltage

masahiko shimizu

Other Parts Discussed in Thread: DS90CR485

My customer is using DS90CR485.
I think PRE-pin pull-up max voltage is Vcc level from P11 of datasheet.
But my customer desgined that pull-up voltage is 3.3V.
Because my customer thinks that this pin has Vcc3v tolerant.

In case of 3.3V pull-up voltage at PRE-pin, What influence does it have on a PRE- EMPHASIS function?

Thanks
Shimizu

over 9 years ago

0 Mike Wolfe over 9 years ago

TI__Expert 3050 points

Hi Shimizu-san,

If the customer would like to have 3.3V tolernat I/O they need to tie pin 79 to 3.3V Vcc. I have attached the schematic for the old EVM, CLINK3V48BT-133.

2577.CLINK48BT-133 PCB SCH.pdf

Mike Wolfe

DPS APPS / SVA

0 masahiko shimizu over 9 years ago in reply to Mike Wolfe

Guru 11235 points

Hi Mike-san

Than you for your support.

They tied pin 79 to 3.3V.

In case of 3.3V pull-up voltage at PRE-pin, What influence does it have on a PRE- EMPHASIS function?

Datasheet suggest max pull-up voltage of PRE-pin is Vcc. Max Vcc is 2.62.

Thanks

Shimizu

0 masahiko shimizu over 9 years ago in reply to masahiko shimizu

Guru 11235 points

Hi Mike-san

Thank you for your support.

My customer has tied 79-pin to 3.3V.

But P11 of datasheet suggests that "Pre-emphasis strength is set via a DC voltage level applied from min to max (0.75V to VCC) at the “PRE” pin".

Max Vcc is 2.62V from datasheet.

When 3.3V pull-up is supplied at PRE-pin, should I think PRE-pin is pulled up by 2.62V as Pre-emphasis function?

Is it possible that PRE-pin is supplied by 3.3V pull-up?

Thanks

Shimizu

0 Mike Wolfe over 9 years ago in reply to masahiko shimizu

TI__Expert 3050 points

Hi Shimizu-san,

I was not able to find an answer to this question in the product archives. We will test this on the bench and get back to you soon.

Mike Wolfe

DPS APPS / SVA

0 masahiko shimizu over 9 years ago in reply to Mike Wolfe

Guru 11235 points

Hi Mike-san

Thank you for your support.

Any update on this?

Thanks

Shimizu

0 Mike Wolfe over 9 years ago in reply to masahiko shimizu

TI__Expert 3050 points

Hi Shimizu-san,

We have located the necessary materials to test this on the bench. We should have a reply for you today, or tomorrow at the latest.

Mike Wolfe

DPS APS / SVA

0 Michael Lu (Santa Clara) over 9 years ago in reply to masahiko shimizu

TI__Mastermind 29635 points

Hi Shimizu-san,

I worked with Mike to test the DS90CR485 on the bench using the CLINK3V48BT-133 eval board.

Yes, I verified that if you choose to make the pre-emphasis pin 3V tolerant, the pre-emphasis pin can be supplied by a 3.3V pull-up for pre-emphasis function.

On the bench, at maximum pre-emphasis (minimal R_pre pull-up), the waveform is identical when R_pre is tied to 3.3V when VCC3 pin = 3.3V and when R_pre is tied to 2.5V when VCC3 pin is tied to 2.5V.

If VCC3 pin 79 = 3.3V, the pre-emphasis pin is 3.3V tolerant as well. If VCC3 pin 79 = 2.5V, the pre-emphasis pin is 2.5 V tolerant (i.e. 0.75 V to Vcc you referred to in the datasheet).

Thanks,

Michael

0 masahiko shimizu over 9 years ago in reply to Michael Lu (Santa Clara)

Guru 11235 points

Hi Michael-san, Mike-san

Thank you for your support.

I understood your information.

It was a great help.

Thanks

Shimizu

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DS90CR485 PRE-pin pull-up voltage