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PCA9534 voltage level instability

brunomusw
Prodigy 120 points
Other Parts Discussed in Thread: PCA9534

Hi...

I'm using an optocoupler that on it's output has a pull-up resistor (100K) and a filter cap. connected to the collector and emissor to ground. My Vcc = 5V.

When the PCA9534 isn't solder on the board and the opto input is off, I have the collector output voltage 4.81V. BUT when I put the PCA9534 on the board this voltage stay instable, like swings from 1.4V to 3V. I didn't leave any I/O of the PCA9534 floating, the unsed I/O are connected to gnd and even the INT, SDA e SCL is connected to Vcc trough a pull-up resistor (10K). As the PCA9534 datasheet's say, on power-up all the I/O are configured as input. 

I'm losing a lot of time on this, and it seens that PCA9534 is wining...

 

Regards,

Brunomusw

  • 0
    TI__Genius 9085 points

    Hi Brunomusw,

    Do you have a schematic so I can see how the PCA9534 is configured?  What voltage is swinging from 1.4V to 3V?

  • 0 in reply to Hattie
    Prodigy 120 points

    Hi Hattie.

    That´s is the voltage swinging, from 1.4V to 3V, or when I turn on the board and it goes up to 3.7V and goes down and stay swinging.

                                   

    The SDA, SCL and INT goes to other board, on the right side, is one of the input of the PCA, that´s in trouble. Even if I connect only a pull-up on the input, the PCA input doesn´t goes to 5V (rail). Does the I2C lines could change the inputs of the PCA, if it isn't working ok?

    Regards,

    Brunomusw