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PCA9536: POR requirements to avoid random values in polarity register

domenyko
Genius 9655 points
Part Number: PCA9536

Dear all,

one of my AA is experiencing some issues with the PCA9536. The polarity register starts wiht not default values.

I've doublechecked the POR, on the power off the device seems to be in spec, see below: (blue line is the VCC), the TOFF is 1.2s

On the power up VCC reaches the VPOR in 8.5ms and then from VPOR to nominal VCC (3.3V) it takes 4ms. So the total trise is higher than 10ms. It is agains DS suggestion.

Since the PCA9536 can work from VCC=2.3V , is it possible to say that the rise time from 0 to 2.3V is less than 10ms ?

Are there any time spec between VPOR a nominal VCC ?

regards,

Domenico

  • 0
    TI__Mastermind 49130 points
    Hey Domenico,

    "Since the PCA9536 can work from VCC=2.3V , is it possible to say that the rise time from 0 to 2.3V is less than 10ms ? "
    The datasheet defines rise time for PoR to be from 0V to Vcc, in this case I believe your rise time is not 8.5ms but something slightly larger than 10ms.

    How much capacitance do you have on Vcc of the device? I am wondering if you can lower the capacitance to help the rise time. Lowering the output impedance of your power source would also help to get a faster rise time on Vcc.

    Thanks,
    -Bobby
  • 0 in reply to BOBBY
    TI__Genius 9655 points

    Hi Bobby,

    the customer was able to manage the ramp up of the voltage supply adjusting a delay circuit present on the board.

    The voltage supply reaches 3.3V in 8.3ms.

    thanks,

    Domenico