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DS125BR820: DS160PR410, output state when no input signal

Taketo Sato
Genius 10325 points
Part Number: DS125BR820
Other Parts Discussed in Thread: DS160PR410

Hello team,

I have question on (1) DS125BR820 and (2) DS160PR410.

In case input pins(such INA_0+/INA_0-, RX0P/RX0N) are open, what state will be seen on output pins(such OUTA_0+/OUTA_0-, TX0P/TX0N)?

If there is a setting method to fix the output state during input is open, please let me know.

If (1) and (2) behave differently during open input, it would be helpful if you could answer above in each cases.

The background of the question is that input has AC coupling capacitor and I would like to consider a way to fix output state when there is no input signal.

Best regards,

  • 0
    TI__Mastermind 24998 points

    Hi Sato-san,

    Can you clarify the issue that is occurring as a result of the output state while there is no input signal?

    For both devices, I expect some DC bias to VCC on the output while the device is powered with no input signal. This bias cannot be changed with any device settings.

    Measuring the output directly during this state is recommended to confirm the biasing point.

    Thank you,

    Evan

  • 0 in reply to Evan Mayhew
    TI__Genius 10325 points

    Hello Evan-san,

    Thank you for your comment.

    I understand output should be fixed state when there is no input and we cannot control the state.

    Could you confirm which Low or High will be seen on output?

    Evan Mayhew said:
    Can you clarify the issue that is occurring as a result of the output state while there is no input signal?

    If output state fluctuates it may interfere resulting in noise so want to avoid it by making the output state fixed.

    Best regards,

  • 0 in reply to Taketo Sato
    TI__Mastermind 24998 points

    Hi Sato-san,

    I expect the output to be pulled to VCC after power-up with no signal, and have no fluctuation afterwards.

    Please allow me some time to see if we have an EVM on-hand I can use to confirm this.

    Thank you,

    Evan

  • 0 in reply to Evan Mayhew
    TI__Genius 10325 points

    Hello Evan-san,

    Thank you for your help.

    If it takes time to prepare EVM, it is helpful if you could confirm this with design or system team.

    Best regards,

  • +1 in reply to Taketo Sato
    TI__Mastermind 24998 points

    Hi Sato-san,

    I was mistaken, there may be concern of fluctuation on the output for either device while powered with no input signal due to the AC coupling.

    For DS125BR820, there is register "PWDN Channels (0x01)" that can be used to disable individual channel output drivers. There is also a pin control option for this setting on pin 25, although the register control may allow for more flexibility.

    For DS160PR410, pins PWDN1 and PWDN2 can be used to disable each channel output driver.

    I was not able to observe any noise on the output while testing comparable parts with the channel output driver disabled.  

    Thank you,

    Evan

  • 0 in reply to Evan Mayhew
    TI__Genius 10325 points

    Hello Evan-san,

    For DS160PR410, what output state will be seen regardless of input signal in case disabling output driver by PWDNx pin?

    Is it the spec of VTX-IDLE-DIFF-AC-p, min 0mV, max 10mV?

    Best regards,

  • +1 in reply to Taketo Sato
    TI__Mastermind 24998 points

    Hi Sato-san,

    Yes, VTX-IDLE-DIFF-AC-p is the correct spec to reference for AC output fluctuation while the output driver is disabled.

    Thank you,

    Evan