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LMZ23610: Synchronising to an external clock using the SYNC input

Peter Martin
Prodigy 200 points
Part Number: LMZ23610

Hi,

I have a LMZ23610 configuration in negative output mode to generate -6V at 6A maximum from a 12V input.

My question however, is general and concerns the use of the SYNC input. I would like the regulator to start up and generate the output voltage first.

Then after this start driving the SYNC input to synchronise the switching to my application circuit for low noise operation.

What is the recommended method of doing this? The datasheet states that the SYNC input must be grounded by <1.5K ohms to select internal clock. What is the voltage threshold? This would be more useful when designing the circuit.

I am aware of the need to level shift the SYNC input when using the regulator for a negative output, but this is not the important part of the question.

Thanks in advance.

Cheers Peter

  • 0
    TI__Guru 50120 points
    Hi Peter,

    The typical input voltage threshold to the SYNC pin is 1.4V but it is recommended to overdrive the threshold by a factor of 2 (eg. VSYNC=3.3V) through the 1.5K ohm resistor. Afterwards the switching frequency of the dc-dc will be based on your preferred external frequency settings.

    Regards,
    Jimmy
  • 0 in reply to Jimmy Hua
    Prodigy 200 points

    Hi Jimmy,

    Thanks for the prompt reply.

    I have implemented a circuit using a 3V3 regulator and an opto coupler. The output transistor stage in the opto does the switching of the SYNC input between 3V3 and 0V.

    The opto itself does the level shift to translate between standard logic levels and the shifted inputs of the LMZ23610 when operating in negative mode.

    Thanks again, cheers Pete