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LM25117: Maximum Current limited to 17A (Webench), why? and using it asconstant current driver

Philipp Putzer1
Prodigy 60 points
Part Number: LM25117

Hi,

I've a question regarding the maximum current of the LM25117. By using external FETs and an user selectable shunt resistor, there should be no limits to the converter IC?

When I try to enter 20A/3V in the webech tool, it states that the limit is 17A. Is this only a limit of the tool or are there some technical limitations?

My second question targets the usability of the chip as a constant current converter for LED/Laser driver application. Currently I'm using the part as sync. buck converter for 5V and 3V3, for this it works very well.

Can I use the current monitoring feature as feedback info to an external error amplifier which compares a set value (DAC output) for output current setpoint? The reference value is fixed internally so I cannot change it.

Is there any application note availble showing how a voltage feedback converter could be transfered to a "current feedback" converter?

Thanks a lot

Philipp

  • 0
    TI__Mastermind 27470 points

    HI

    for first question, LM25117's drive limit the max output current, cause the switching loss is relate to Vin, Io ,tr, tf and fsw. when Io is higher, the drive loss will be larger. we more suggest you use low frequency to reduce the mosfet switching power loss

    for second question, you can refer

    Thanks