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PCA9539: Output Waveform

KHR
Prodigy 40 points
Part Number: PCA9539


Hi, Team.

I'm using PCA9539 IC for controlled LEDs.

In order to operate the LED, 'H' was allocated on the P-Port.

Our VCC is 3.3V.

Then shouldn't there be 3V in the P-Port out level?

However, about 1.4 V (Vrms) is output as the square wave came out.

Is it the characteristic of Chip to came out a square wave? If not, do I have to set it up separately?

Thank you.

Best Regards.

  • 0
    Guru 318700 points

    What current are you trying to draw out of the pin?

  • 0
    TI__Guru 53575 points

    Hi KHR,

    The drive a P-port pin as an output, the relevant bit must be set to 0 in the configuration register. The pin can then be driven high (Vcc) or low (GND) based on the value written to the corresponding bit in the output register. 

    The pin output state will only change when the value in the output register changes (or the configuration changes to input). If you are observing a toggling behavior on this pin, it is most likely caused by periodic writes to the output register or the signal is being driven by an external source (and the P-port is high-z). Make sure there is no extraneous writes occurring to PCA9539 during the observed square wave and double check that the configuration sequence satisfies the description above. 

    I cannot see the image you shared. Can you please try posting again? Using Insert->Image/video/file seems to work best. Also, I'm not sure what you mean by " 'H' was allocated on the P-Port". Does this refer to a '1' being written in the output register?

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    Prodigy 40 points

    Hi Eric,

    I attach the image I attached again.



    Does this refer to a '1' being written in the output register?

    => Yes, it is.

    The pull-up resistance of I2C is connected to the MICOM side by 2k ohms.

    P-Port is being used as an output.

    And each of the ports is connected to the base end of the transistor for operating the LED.

    As I know, the output current of PCA9539 is 25mA per port, and the output current of all ports should be 100mA or less.

    It seemed to be a current shortage problem, but calculated it was 0.23 mA per port. (16 channels in total, 4mA)

    First, I asked our S/W team to review the register value, and I'll tell you the result.

    If there is any other solution, please reply.

    Thank you,

    Best Regards.