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UCD3138064: PMBUS connection

Mia Ma
Intellectual 2365 points
Part Number: UCD3138064

Hi team,

I have a confusing question about the PMBUS connection.

There are two kinds of resistor value in series with PMBUS_CLK and PMBUS_DATA

(1)33.2ohm

(2)100ohm

if there is a design guideline for these resistors? the value and the power loss?

could you give some explannation about it's function.

Thanks

Best regards

Mia Ma

  • 0
    TI__Genius 17090 points

    Mia, I believe those resistors are to limit the current into the protection diodes which go to ground and V33.  The circuit is to protect the board from a voltage outside the 0 to 3.3 volt rails of the chip.  This can be either from ESD (ElectroStatic Discharge) or from an actual voltage mismatch.

    In a typical customer system, where the PMBus is permanently connected and on the same board, this protection is not necessary, and the diodes and resistors should be omitted.  The diodes add a fair amount of capacitance, and the resistors obviously add resistance as well.  

    It's only useful in something like an EVM, which gets its PMBus plugged and unplugged all the time.  

  • 0 in reply to Ian Bower
    TI__Intellectual 2365 points

    Hi Ian,

    Noted it, and thanks a lot.

    Best regards

    Mia Ma