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DS90LV049: How to reverse output state from "H" to "L" in Fail-safe status

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Replies: 3

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Part Number: DS90LV049

Hi support team.

My customer is considering to use DS90LV049.

They want to get output state "L" in fail-safe status(Input open or short).

Please tell me how to reverse output state from "H" to "L" in faile-safe status.  

We think we can do if we pulled up RIN- to VCC and pulled down RIN+ to GND, is that correct?

We assume pull-up and down resistor are 3-5kohm.

Best regards.

Higa 

  • It is possible to reverse the polarity of the output failsafe using external bias resistance.  The actual values may need to be lower since they also need to overcome the internal bias of the LV049 to try to output a logic "1" in failsafe mode.

    Regards,

    Lee

  • In reply to Lee Sledjeski:

    Hi Lee-san

    Thanks for your quickly reply.

    I think that worst case of the internal bias current of the LV049 is ±12uA.

    I  estimate the value of pulled-up and pulled-down resistor are less than 1kohm, is it correct?

    (Please refer to the attached .docx file)

    I would appreciate it if I could get your more advice.

    Best regards.

    HIgaReverse output polarity in Falesafe mode.docx

  • In reply to higa daisuke:

    Hi Daisuke-san

    The value of the resistors would be greater than 1K ohm.  With 1K ohm resistors the current in the resistor combination of 1K - 100 - 1K would be ~ 1.5mA.  This current would create a 150mV offset across the RIN+/- pins.  I think this is more offset voltage than needed.  I think 2.2K ohm resistors would be enough to do a good job. 

    Regards,

    Lee

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