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RTOS/TCA6424A: Default state for TCA6424A switches and its working

Nitesh Padiyar77
Genius 3745 points
Part Number: TCA6424A

Tool/software: TI-RTOS

Hi,

I am working on TCA6424A (I2C based switch) using TI RTOS driver.

On default i am getting all the switches high, My RESET and INT are connected to Vcc.

After I2C handle creation i am setting configuration register as O/P with all port High.

i.e ->Configuration is done by  8C 00 00 00 is set and O/P are set to high -> 84 FF FF FF ---- Observer all the ports high(5V)

Now if i write 84 00 00 00 for  setting all ports low --> observed O/P ports (3.9v)

Whether i am doing any mistake or on low setting 3.9v sets by default? I assume it  should be 0v, Please confirm

Whether my I2Cbus  is working /not i am confused.

Thanks in advance

Nitesh 

  • 0
    TI__Guru 62910 points
    Hi Nitesh,

    The voltage should be closer to 0 V when the output port state is set to low. Do you have pull-up resistors populated on these output ports? If so, can you please check their resistance value? If the resistances are too low, then the the pull-ups may be counteracting the pull-down effect of the output drivers at each port. If you can share a schematic showing the usage of the part it would be very helpful as well.

    Regards,
    Max
  • 0 in reply to Max Robertson
    Genius 3745 points

    Hi Max,

    So we don't have the pull up resisters. Below is circuit diagram for your reference

    Its application circuit diagram

    Let us know your comments

    Thanks in advance

    Nitesh

  • 0 in reply to Nitesh Padiyar77
    TI__Guru 62910 points
    Nitesh,

    Thanks for the schematic. Are you measuring the output voltage directly at the TCA6424A or at the photo-relay? The reason I ask is that the LED in the relay has a forward voltage of about 1.1 V, so it would make sense to measure 3.9 V there whenever it is "on" (i.e., TCA6424A driving low). If you are definitely measuring the TCA6424A output, could you please double-check the resistances R189-R194 to make sure they are 3 kOhm as shown?

    Max