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PCF8574A: Output not latching HIGH

MARK FRANKLIN
Prodigy 30 points
Part Number: PCF8574A
Other Parts Discussed in Thread: PCF8574

IS the 2005 waiver still in affect?

  • 0
    TI__Mastermind 42233 points

    Hi Mark,

    I did a quick google search and have since changed my answer. I believe this has been fixed and updated in the datasheet: 

    The waiver should no longer apply. Data hold time can be a minimum of 0ns. 

    Are you seeing otherwise? 

    Do you have waveforms to show what issue you are dealing with here (OUTPUT not latching HIGH)? 

    Regards,

    Tyler

  • 0
    Prodigy 30 points

    Thank you kindly for the prompt response.  The PCF8574A does not function as expected on a prototype PCB.  The PCF8574T operates as expected in a bench-top circuit verification.  So I suspect that the "A" is nor fixed, and perhaps the "T" is fixed?

  • 0 in reply to MARK FRANKLIN
    TI__Mastermind 42233 points

    Hi Mark,

    I am having trouble understanding how the device fails to function.

    You are saying that the NXP version PCF8574T is passing, but PCF8574A is failing.  

    The PCF8574A and PCF8574 (non-A) have different fixed address bits. As far as I understand, this is the only difference between the two devices. 

    Now the differences between the NXP and TI device I am not certain. How exactly are the devices failing? Do you have scope captures to show what exactly is happing on a waveform level? 

    Regards,

    Tyler