DS90CF386: the method of termination for unused pin

Yusuke Mukuno

Part Number: DS90CF386

Hi Expert,

Please tell me about the method of termination for unused pin .
Conditions:
-There is power supply to the device.
・ Input Low to / PDWN
・ There is no transmitter connection, only the terminal 100Ω connecting each +/- input

1. The LVDS input pins of RxIN0 to RxIN3 and RxCLKIN will float, is that OK?

2. According to the specifications "7.1 Overview", the following is stated, so if you set / PWRDWN to Low, customer understand that it is okay even if there is no valid data input.
"These devices feature a PWR DWN pin to put the device into low power mode when there is no active input data."
At this time, RxOUT0 ~ 27 seem to be Low, what is the value of pull-down resistance ?

3. Does the power consumption in the power down mode typ = 140uA include the current when the input is floating or the output pin is pulled down?

4. When only the device power at the transmitter is shutdown, is there a possibility that the leakage will come from the receiver to transmitter?
Also, if the / PWRDWN = Low is set at that time, will the leakage be eliminated?

Thanks

Muk

over 5 years ago

0 Bryan Kahler over 5 years ago

TI__Mastermind 25955 points

Hi Muk,

Thank you for all of these great questions. To help me better aim the answers, could you please give me a more of an idea of the application you're currently designing with and the problems you're currently facing? Are you experiencing current leakage issues or higher than expected current consumption in power down mode?

There are some great resources available for designing in LVDS. This guide is older, but comprehensive: http://www.ti.com/lit/ug/snla187/snla187.pdf

Also, the interconnect design-in guidelines for this device may be of use: http://www.ti.com/lit/an/snla002/snla002.pdf

Sincerely,
Bryan Kahler

0 Yusuke Mukuno over 5 years ago in reply to Bryan Kahler

TI__Expert 7395 points

Hi Bryan-san,

No, they don't have any issue. it is just question for their design.

Could you please answer for each questions?

Thanks

Muk

0 Bryan Kahler over 5 years ago in reply to Yusuke Mukuno

TI__Mastermind 25955 points

Hi Muk,

Glad to hear you aren't currently experiencing any issues with the device. Please let us know if you run into any questions when you're able to evaluate the part on the bench.

With respect to:

This is answered in detail with respect to serializer and deseralizer in this collateral, given above: http://www.ti.com/lit/an/snla002/snla002.pdf

Still working on the other questions with systems and design. Expect an update by Tuesday.

Sincerely,
Bryan Kahler

0 Yusuke Mukuno over 5 years ago in reply to Bryan Kahler

TI__Expert 7395 points

Hi Bryan-san,

Do you have any update?

Thanks

Muk

0 Bryan Kahler over 5 years ago in reply to Yusuke Mukuno

TI__Mastermind 25955 points

Hi Muk,

Here are the answers to the remaining questions:

1) Unused LVDS inputs can be left open (but terminated with 100ohm) since there’s failsafe bias circuitry

3) Powerdown current is based on floating inputs

4) No, LVDS inputs are tri-stated under power up and down conditions

Sincerely,
Bryan Kahler

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DS90CF386: the method of termination for unused pin