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TCA9555: LED driver settings of TCA9555

Watson
Expert 3835 points
Part Number: TCA9555
Other Parts Discussed in Thread: TCA9535

Hello Champs,

WE would like to use pin11 and pin12 of TCA9555 to support LED driving feature.

Vcc=3.3V, pni11 and pin12 are connecting to LED and up resistor to 3.3V system power.

Can you help to know what is the GPIO setting for Pin11 and Pin12 and also if this LED connecting is ok with the 3V3 system power?

Thanks.

  • 0
    TI__Guru 72861 points

    Hi Watson,

    You would first set the output register 0x03 to be XXXX X00X (0x00h would work). //set port1 p1 and port1 p2 to be low if set as an output

    Then to turn the LED on, you would write to the configuration register 0x07 to be XXXX X00X. //set port1 p1 and port1 p2 to be outputs

    To turn the LED off, you would write to the configuration register 0x07 to be XXXX X11X. //set port1 p1 and port1 p2 to be inputs (HI-Z)

    Thanks,

    -The champ Bobby

  • 0 in reply to BOBBY
    Prodigy 20 points

    Hello ,

    Our problem is to set P11 & P12 to INPUT and not have INTERNAL PULL HIGH or LOW.

    thanks~

    berg~

  • 0 in reply to berg lai
    TI__Expert 3835 points

    Champs,

    Berg want to confirm again for LED on/off, the output shall be setup a OUTPUT so no influence to internal pull up/down ckt?

    Thanks.

  • 0 in reply to Watson
    TI__Guru 72861 points

    Hi Watson,

    If you set the pin to be an output HIGH, the internal pull up resistor will essentially be bypassed and because the LED has no potential difference across it, the LED will be off. 

    If you set the pin to be an out LOW, the internal pull up resistor will have a path to GND and will leak some current that way (by the way, the LED will be turned on since it now has a voltage drop across it). 

    If you are concerned about leakage current, then using the TCA9535 would be a more suitable approach since it removes the internal pull up resistor. If you don't mind the leakage current then this should not be a problem for you.

    -Your one and only Champ Bobby

  • 0 in reply to BOBBY
    Prodigy 20 points

    Hi ~

    We use TCA9555RGER to read the DIP Switch value.
    We have written to the configuration register 0x07 to be XXXX X11X. so, port1 p1 and port1 p2 to be inputs (HI-Z) now.


    But we discover it have an internal pull up resister in the IC, and this will affect the voltage level.
    Our question is :
    How to close the internal pull up resister when we configure IO pin to input?
    We hope the internal pull up resister is disable.

        thanks~

    berg~

  • 0 in reply to berg lai
    TI__Guru 72861 points

    Hi Berg~

    Unfortunately, our 9555 device does NOT have the ability to disable the internal pull up resistor. If the internal pull up resistor is a problem, then I think the next best solution would be to replace the TCA9555 with the TCA9535 which comes in the same package.

    Bobby~