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PCF8575C: PCF8575C latch issue

Part Number: PCF8575C
Other Parts Discussed in Thread: PCF8575,

Hi Team,

In one of the design customer want to keep pin 7 state at HIGH permanently and accordingly they are writing the registers using I2C. But, not seeing the state at HIGH, rather a pulse momentarily at HIGH and going to LOW. 

The device is supposed to latch the status but it is not happening. 

Could you please help with inputs to address this issue. 

Regards, Shinu Mathew

  • Shinu,

    Great to hear from you. In your application, you will need a push-pull architecture for the output. For this, I recommend switching to the PCF8575 instead of the PCF8575C. This should fix the issue (and also reduce cost).

    Here is further explanation:

    On the block diagram of the PCF8575C (currently in your schematic) we can see that it just uses an open-drain output.

    This is why your customer sees only a temporary high.

    On the contrary, the PCF8575 uses a push-pull architecture.

    This should allow for the line to be driven high and remain there.

    My recommendation is simply replace PCF8575C with PCF8575! :)