I am using I2C port of FX3 controller to talk to led driver chip. The LED driver chip has registers that can be accessed through I2C bus. FX3 chip is the master device.  In the partial drawing below. SCL_M and SDA_M are I2C signal from FX3 controller and are pulled up to 3.3V through 1k resistors at the controller side.  SCL and SDA are I2C from led driver chip. When I install R19 and  R15 only, FX3 has no problem to access registers of LED driver chip. But when I removed R19 and R15, install U8(LTC4301), R22, R23 and C17 only, FX3 controller can't access registers of LED driver chip anymore. Please let me know what could it be the reason.

Thank you very much. I am in the middle of debugging the prototype  board.

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    •  Analog Employees 
    on Nov 7, 2018 2:37 PM in reply to Kelly166

    Hi Kelly,

    With a 3.3V pull-up supply for SDAIN and SCLIN you should try the LTC4301 rather than the LTC4301L. The LTC4301L has levels for lower voltages. 

    Can you get a pull-up and probe on the READY pin to see what state its in? The READY pin should be high if the buffer is ready to start doing its thing.