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PCA9554: Losing output data / config

Brian Merkel
Prodigy 10 points
Part Number: PCA9554
Other Parts Discussed in Thread: TCA9554

Hello,

I am using the PCA9554 to drive output enable signals for load switches. All of the IO are configured as outputs at all times and during normal operation, some of the outputs that should be low (0V) are outputting 0.75V-0.815V. This causing load switches to turn on where they should not be. Only 3 of the 8 outputs are exhibiting this behaviour. The outputs that are correctly driven low are measuring 0.08V. All IO pins have 10k external pulldowns. The 3V3 rails looks healthy. Maybe 3 outputs somehow got configured as inputs? The only thing that gets the part out of this state is to full power cycle the 3v3 rail. 

Any ideas on what could cause this?

Amy

  • 0
    Prodigy 10 points

    Completely removing the load switches from the outputs so the only load is the 10k resistor, we still see the output at 0.7V. 

  • 0
    TI__Mastermind 24981 points

    Hey Amy/ Brian,

    The I/O ports are configured as inputs on startup by default, so it needs to be configured as outputs first. What is the IOL measured at the output? Are you able to provide the schematic so I can further take a look? 

    Regards,

    Jack 

  • 0 in reply to Jack Guan
    Prodigy 10 points

    The I/O ports are configured as outputs (config reg is 00 so that is confirmed). We tried shorting out the 0.7V output signal with a meter set to uA mode to see what would happen - there is at least 20mA behind it and the meter was only able to drag the rail down to ~0.5V.

    There is a 100k internal pull up, and we have an external 10k pull down. We disconnected the load switch circuit so there is no other load at all. It almost like the expander is driving both the high-side and low-side simultaneously. 

    Also, our input and output port registers never agree. For example, after a MCU reset the input port register is FF and the output port register is FB (config reg is 00), where we expect the output reg should to be FF. 

    Amy

  • 0 in reply to Brian Merkel
    TI__Mastermind 24981 points

    Hey Brian,

    Just to confirm, is the device ACK'ing when you write to the device?

    Are you ever able to change the state of the faulty ports? If not, it is possible that the device could be damaged. How many devices has this impacted and does an ABA swap resolve the issue?

    Regards,
    Jack 

  • 0 in reply to Jack Guan
    Prodigy 10 points

    Yes, we are able to change the state of the faulty ports. They are correctly outputting 0V at power up. When we enable them, the output goes to 2.8V. When we disable them, the output only drops to 0.75V (there for are still driving our load switch high). 3x ports exhibit this behaviour and 2x ports on the same IC have an enable voltage of 3.2V and disable voltage of  ~0.08V.  

    We have the board out of the field now and will look at the output on a scope and then try an ABA swap. 

  • 0 in reply to Brian Merkel
    Prodigy 10 points

    We have 3 of these ICs on the board and the one that is having issues is running hotter than the others. It seems the part is damaged. Does the TCA have any additional protection when compared to the PCA?

  • 0 in reply to Brian Merkel
    TI__Mastermind 24981 points

    Hey Brian,

    Looks like the device was in fact damaged in some way (whether it be ESD damage, or operated in conditions above the absolute maximum characteristics in the datasheet). If you are able to provide the waveforms captured on the scope or the schematic, I can try to debug where the source of the issue is. 

    The TCA9554 is the direct upgrade (performance related) from the PCA9554 that fixes the Interrupt Errata (see section 8.2.3.1 of the datasheet) and also supports lower VCC ranges, but their absolute maximum conditions + ESD protection are similar. Also see this FAQ for more information. 

    Regards,
    Jack

  • 0 in reply to Jack Guan
    Prodigy 50 points

    Hey Jack, could you dm me your email address so I can send you the schematic privately?  

    Thanks,

    Amy

  • 0 in reply to Amy Domino
    TI__Mastermind 24981 points

    I have closed this thread as I am following up offline.

    Regards,

    Jack