• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 3 answers
  • Subscribers 33 subscribers
  • Views 432 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DS160PR421: Unused RX input, PD pin stuck to GND

michel counson
Prodigy 50 points
Part Number: DS160PR421
Other Parts Discussed in Thread: DS160PR410

Hello,

For cost reason and easy supply management (single part to buy), we intend to use the DS160PR421 even where we do not need the mux function.

What to do with the unused inputs in this case?

Keep the pins unconnected?

These pins are internally biased due to the AC coupling, but is it allow and better to connect these pins to GND?

In the other hand, we will configure all the DS160PR410 through I2C to have a maximum flexibility (14 components managed with two I2C buses).

 Can you confirm that the PD pin from all DS160PR410 can be permanently connected to GND?

The component does not need at least one high pulse on PD pin to always start up correctly (Rx detect state machine reset is in any case available through I2C Reg 0x0D bit3)?

Could you also confirm that we have no possibility to put some channels/all channels in standby through I2C (available on 75lvpe5421 but not on DS160PR421)?

 

Thank you for your help.

 

Regards

 

Michel Counson

 

  • 0
    TI__Mastermind 20901 points

    Hi Michel,

    • Please note the following previous thread regarding termination of un-used inputs (same logic applies for the DS160PR421): https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1059336/ds160pr822-unused-rx-and-tx-pins 
    • The DS160PR410 has two Power Down pins (PWDN1, PWDN2) to control the power down or power up of the 2-channel banks of the device independently. The PWDN pins on this device can be pulled low always; when the device is powered on in this case, the RX Detect state machine will perform depending on the RX_DET pin state. The RX Detect state machine can be reset through each channel's Register 0xD[3].
    • While I do not believe the power-down register is public in the programming guide, over-writing the desired channel's Channel Register offset 0x5 with 0x80 should power down individual channels. To power them back on, write 0x7F to this channel register.

    Best,
    David

  • 0
    Prodigy 50 points

    Hello,

    Sorry for my typo, all my questions including the question about the PD pin are for the DS160PR421.

    Concerning the way to manage the unused inputs, we have 14 ICs with 4 unused pairs per ICs that means adding 112 resistors and 112 capacitors and degrading the PCB layout?

    The inputs seems already terminated on 50R inside the component, could you explain what will be the improvement expected by adding these resistors and capacitors?

    If direct connect to GND is allowed, this will make better shielding between inputs from different channels.

    Any comments will be welcome.

    Thank you for your help.

    Regards.

    Michel Counson

  • 0 in reply to michel counson
    TI__Mastermind 20901 points

    Hi Michel,

    Thanks for clarifying the part number.

    The termination suggestion is specifically an AC termination, as these signals are AC coupled. These pins can possibly create resonance and cross-talk if not AC terminated. If these outputs are tied directly to GND, any resonance or noise in the GND plane could cause unexpected Common-Mode voltage changes, or potentially damage to the part.

    Best,
    David

  • 0 in reply to David Waier
    Prodigy 50 points

    Hello,

    Thank you for all your responses and comments.

    Could you update your answers regarding the PD pin and particularly your remark about the register 05 taking into account that my question concerns the DS160PR421 (typo in my initial request).

     

    Concerning the way to manage the unused inputs, it will be very difficult for us to place all these additional components without degrading our PCB layout.

    We must be sure that by placing all these additional components, the overall integrity of the useful signals will not ultimately be worse.

     

    Do you have access and could you share a little more details about the DS160PR421 input circuitry?

    The 50R terminations are directly connected to the internal 2V5 global power line or to a dedicated global reference voltage or to an individual reference voltage per differential input?

    These 50R terminations seems to be replaced by a fairly high impedance (20K?) during reset or power down, is it correct?

     

    When an input is not selected, what about termination/biasing of these unused differential inputs?

    • If the DC single ended impedance is still 50R, we could consider that keeping the pad unconnected is not a real problem  (the unused pad won’t really radiate noise to adjacent pins). If we really think it’s better not to leave these pins unconnected, why not connect the 2 pins from a pair together and just put a 1n 0201 capacitor to GND?
    • If the DC single ended impedance is very high when an input is not selected is it really a problem if we connect these pins to GND (if it's not risky to do that, it's the simplest solution regarding the PCB design)?

     

    Please let me know what you think about that.

    Thank you for your support

    Best regards

    Michel Counson

     

  • 0 in reply to michel counson
    TI__Mastermind 20901 points

    Hi Michel,

    Thank you for your response - I understand the concern about additional passive component placement. Please see Nasser's follow-up comments via email as well and we can continue the conversation there as needed.

    Best,
    David

  • 0 in reply to David Waier
    TI__Mastermind 20901 points

    Hi Michel,

    We will continue to follow-up offline. I will close this case to keep communication concentrated to email.

    Best,
    David