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TRS3122E: Auto-powerdown with INVALID.

Scott Mitchell
Prodigy 20 points

Part Number: TRS3122E

Hi,

Is it possible to connect the INVALID output to FORCEON while FORCEOFF is high, to allow auto-powerdown when no cable is connected?

Thanks,

Scott

  • 0
    TI__Guru 54042 points

    Hi Scott,

    So this is actually a new use case I haven't really seen before - so we don't have a ton of examples in practice of this type of application. That being said - I really don't see an issue with it since /INVALID does not care about the states of FORCEON and /FORCEOFF. That being said though - if you have FORCEON pulled low and /FORCEOFF pulled high the device will enter auto-shutdown mode after 30s of no activity on the bus and you can usually leave /INVALID floating - that is the most common use case of this device - and other with auto-powerdown and auto-powerdown +. 

    Please let me know if you have any other questions and I will see what I can do!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Prodigy 20 points

    Hi Parker,

    Thank you for the prompt response.

    I was looking for a way to have the part automatically power down when not connected, but not have any latency when transmitting a message. If I connect FORCEOFF high and FORCEON low, then the charge pump will shut down but it will take too long to power up again if there's a transmission.

    With FORCEON connected to /INVALID, the part will only be powered-down if there's no cable connection, otherwise, it will remain powered.

    Thanks,

    Scott

  • 0 in reply to Scott Mitchell
    TI__Guru 54042 points

    Hi Scott,

    Alright - I see what you are trying to do - just to clarify I want to make sure that it is clear what will happen, from a high level, to make sure there is no confusion and for anyone who may read this thread in the future. 

    /FORCEOFF VOLTAGE ON RIN /INVALID FORCEON Device State
    HIGH -0.3V >= Vin >= 0.3V

    LOW

    (typical high to low delay  30us)

    		 LOW auto-power down -> after 30 seconds of Invalid RIN level Device Shutdown 
    HIGH 0.3V > Vin >= 2.7V Indeterminate Indeterminate Indeterminate
    HIGH -2.7V <= Vin < -0.3V Indeterminate Indeterminate Indeterminate
    HIGH Vin > 2.7V or Vin <-2.7V

    HIGH

    (typical low to high delay is 1us)

    		 HIGH Device Forced On

    So there is some risk when VIN is in-between 0.3V and 2.7V (and -0.3V and -2.7V) - under normal operating conditions it really  shouldn't be that much of an issue because normal communication won't typically cause issues on the /INVALID output. 

    Please let me know if you have any other questions and I will see what I can do.

    Best,

    Parker Dodson

  • +1 in reply to Parker Dodson
    Prodigy 20 points

    Hi Parker,

    Without a cable connected, Vin should be essentially 0V if we can take the datasheet at face value. It shows internal pull-downs on both RIN inputs. So it would appear that connecting the /INVALID output to the FORCEON input while /FORCEOFF is high, should do what I want.

    I've ordered an eval module. I'll let you know if it doesn't work as predicted.

    Thanks for your assistance,

    Scott