• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 33 subscribers
  • Views 1026 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.

SN65HVS885 without supply

Jottm
Prodigy 100 points
Other Parts Discussed in Thread: SN65HVS885

We want to use the SN65HVS885 for 12V to 24V digital inputs. In our application we cannot make sure that there is always the 5V supply present when there is a voltage on the digital input pins.

What currents on the inputs have to be expected when the IC has no supply, and to which pins do the currents flow?

Are there any other hints when using the ic in this configuration?

  • 0
    TI__Guru 62920 points
    Hi Joerg,

    There shouldn't be a risk of device damage in this case (as the absolute maximum ratings are specified independently from the supply voltage), but as for the exact currents I am not sure. I will see if i can set this test up in our lab this week to see what typical behavior can be expected.

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Prodigy 100 points

    Hi Max,

    thank you, that sounds good. I am waiting for your results.

    Regards,

    Joerg

  • 0 in reply to Jottm
    TI__Guru 62920 points
    Hi Joerg,

    Sorry for the delay in getting back to you. I was able to run the test today. I used the EVM board; the schematic can be found in the User's Guide here:

    www.ti.com/.../slau275.pdf

    This board uses input resistances (R0:7) of 1.2 kOhms on each input pin. I applied 24 V to the input side of each resistor (i.e., at JMP1) and measured the input current with an ammeter. The board was grounded, but no VCC rail was connected. The input current was about 76 uA for each pin.

    Please let me know if you would like any further testing performed under different conditions (e.g., different input resistor values, etc.).

    Best regards,
    Max
  • 0 in reply to Miguel Robertson
    Prodigy 100 points

    Hello Max,

    thank you for doing the test.

    Can you confirm that the current into the input does not flow to the VCC or one of the logic pins and "backpower" other parts of the circuit? We have 16 inputs in our application so the 75uA per channel might add up to a significant current.

    Best regards

    Joerg

  • 0 in reply to Jottm
    TI__Guru 62920 points
    Joerg,

    I revisited the same set up as before, but this time connected +24 V to every input of the device. The total input current was still about 75 uA per pin. I probed each other pin (including VCC) with a multimeter, and each one had a voltage that was less than 1 mV.

    Max