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LSF0102: Part A has no output

user5109803
Prodigy 10 points
Part Number: LSF0102

Hi

    I have a project that use LSF0102. Specific application is as follows: the 1.2V MDIO bus is converted to 3.3V MDIO through a LSF0102, and then converted to 1.2V  MDIO bus through another LSF0102.

But when the actual measurement I found: When the MDC signal from the low level to the high level is Ok, there is a 3.3V output; but then 3.3V MDC by the second pieces of LSF0102to 1.2V, there is no output.

Can you please  help me to analyze the reason?  Thank you!

the below is the circuit:

And:

       the circuit of 1.2V to 3.3 and 3.3V to 1.2 is same, the difference is  the circuit of 1.2V to 3.3 : A is input, B is output;  the circuit of 3.3V to 1.2 : B is input, A is the output.

      the MDC rate is 2.5MHz.

  • 0
    TI__Guru* 96842 points
    Hi,
    Can I ask why you're converting from 1.2V to 3.3V and back to 1.2V, and not just connecting 1.2V to 1.2V?

    It looks like your pulll-up resistor values on the 1.2V side are 60.4 ohms and the 3.3V side is 200 ohms - is that correct? If so, the required sink current of your drivers is ~37mA just for this one stage. I haven't seen a 1.2V device that can drive that much current, so that's probably where the issue is.