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TCA9539-Q1: TCA9539-Q1 output flicker at initialization

Part Number: TCA9539-Q1

Hello, I am using TCA9539-Q1 (IO Expander). I am attaching my schematic. I want to use IO expander as OUTPUT so I have configured both port as output. I need the output to be low at power up so I write "0x00" to both output port (as datasheet says output is by default high). On writing the output port as "0x00" ; All pins becomes high for ~89us ; because of this my load becomes high for some time which is undesired behavior. 

Is it possible to set the output low by default without the voltage output high glitch?

  • Hi Alihussain,

    Are you writing to the output register first THEN the configuration register?

    I assume you are actually writing to the configuration register first which causes the line to be 'HIGH' until you finally write to the output register. Doing it in the opposite direction (output register first followed by configuration register) should allow for you to avoid the 'HIGH' state.


  • Thanks @Bobby,

    You identify it correctly, I was doing configuration register first and then output register because it is not mention in datasheet. Now I did what you told and it solved my problem.