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DS90UB949A-Q1: I2C problem

Peter Berenji
Prodigy 20 points
Part Number: DS90UB949A-Q1
Other Parts Discussed in Thread: TXB0106, TXS0108E-Q1

Hello

I am using subject serializer on my designed PCB. I have OK picture, register 0x5A is telling me that everything as should be relating to HDMI input and FPD III Link as output.

Problem is that I can use I2C only on 3V3 Level. If I try to go to 1V8 level via TI shifter TXB0106 with I2Csel pin tied to 1V8 via 10K, communication is sporadic, and quite often I have oscillations on SDA line.
Note that when I am using TXB1006 I am skipping pull ups on 1V8 side (as per datasheet off TXB1006). 
Part of schematic related to it is attached. 
Any suggestion why it happens?


Thanks 
Peter
Continental Automotive

 

  • +1
    TI__Mastermind 34135 points

    Hi Peter,

    The I2C pins on the UB949 are open-drain and cannot be left floating as per the datasheet. The datasheet of the TXB0106 states that it should not support applications such as I2C.

    I recommend using a TI voltage translator that can operate on open-drain logic such as the TXS0108E-Q1.

    Best,

    Jack