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TCA9539: TCA9539 Power on can't be detected

user4979899
Expert 3080 points
Part Number: TCA9539

Hi Sir,

My customer design TCA9539 with PCA9546 from I2C master CP2112(I2C host, USB-to-SMBus controller) under Linux OS,

Linux will scan all I2C slave address after power on in the beginning, but TCA9539 can’t be detected,

We set TCA9539 address as 0x74, and you can see it can’t detect as below, and customer need to do the I2C Read/Write on TCA9539 then re-scan the device, then TCA9539 will be detected,

Please see below log and also schematic for reference,

 

And I also ask customer to reset TCA9539 after power on and before they scan the I2C address,  it still cannot detect TCA9539 in Linux shell.

BTW, TCA9539 can be detected based on the procedure which do the read/write to TCA9539,

but it’s very weird TCA9539 will disappear again after resetting TCA9539. It needs to do the same procedure (Read/Write)to find TCA9539 again.

 

Customer also capture some waveform as below, FYI

Could you please help to give some guide to advise it?

Thanks

  • 0
    TI__Guru 60540 points

    Hey Anne,

    The issue is the TCA9539 needs to have it's internal pointer addressed before you can perform a read transaction. (This is because the device has multiple registers and it does not know which register you want to read.)

    A write transaction must be performed before this device can ACK to a read. This is discussed in the datasheet:

    -Bobby