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SN65C1167: Powering Up/Down Behaviour

Thomas Baumgartner
Prodigy 10 points
Part Number: SN65C1167
Other Parts Discussed in Thread: LM809

Hello,

i have the problem of data inconsistensy at powering up and down the transceiver.

My question is therefore: Can the Receiver-Enable Input-Pin (and correspondingly the High Impedance State of the Receivers Output) be used safely when Vcc is in the range of 1.5V ... 4.5V?

Thank you in advance,

Best regards,

Thomas Baumgartner

  • 0
    TI__Guru 53252 points

    Hi Thomas,

    We don't guarantee operation outside of rec. operating range - so VCC = 4.5V to 5.5V. Outside of that range and the device may exhibit unexpected behavior. 

    That being said - to avoid damage on the /RE pin (as you are holding it high) - it should be pulled up to VCC through a resistor so that the /RE pin doesn't every have a value of VCC + 0.5V (after that an input diode will shunt current to the VCC rail and can cause damage to the internal of the transceiver) - this will be the most advisable way to keep R high-Z during power up and power down.

    What are the issues that you are seeing with the application however? Is the R output sending out a signal during power up/down? 

    Please let me know as I want to better understand the specific issue you are seeing to see if there could be another culprit for the issue itself.

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Prodigy 10 points

    Hello,

    first of all - thanks for your promt reply.

    The /RE pin is tied to Vcc (without a resistor) at the moment.

    The SN65C1167 is used for Gate Drive Signals of a half bridge module (it is connected further to your isolator ISO7841FDWW(R)).

    When powering up or down the system, which is consisting of the SN65C1167 and the isolator, the SN65C1167 has undefined output levels (which are also changing, like random oscillations) and - since the isolator starts working at latest with Vcc>2.25V the half bridge receives wrong switching commands until Vcc reaches approximately 4V and the SN65C1167 starts working regulary.

    Therefore the idea was, to hold the /RE pin down using a Power-Good Indicator IC (something like your LM809/810).

    My other option is using this Power-Good Indicator IC and a And-Gate which starts working before 1.75V (lowest voltage where the isolator may work) and put this gate inbetween the SN65C1167 and the isolator.

    But maybe i just missed a simple and effective solution Slight smile

    Best regards,

    Thomas Baumgartner

  • 0 in reply to Thomas Baumgartner
    TI__Guru 53252 points

    Hi Thomas,

    I think based on the issue that you are seeing the problem can be explained by the lower operating voltage during the powering procedures - it sounds like the logic and receiver thresholds aren't working as they would during 4.5V to 5.5V operation (the device working at ~4V makes sense w.r.t. to our ratings). I don't think there is damage necessarily as nothing you have done seems to indicate a damage causing scenario but more that the device internals are not being biased properly to work as intended when the supply voltage is too low. 

    With that being said I do think the AND gate would be the best solution as it should prevent the glitchy data from propagating past the gate during power-up / power down. As the transceiver itself may have some issues under 4.5V with respect to functional operation  but the AND gate could potentially hlep prevent that. 

    Please let me know if you have any other questions!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Prodigy 10 points

    Hello,

    thank you for your information - i will resolve my issue using a AND-Gate.

    Best regards,

    Thomas