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LM5050-2: RDS on issue

Patrick Chen
Mastermind 8875 points
Part Number: LM5050-2

Hello,

              The datasheet show the recommend RDS as below. But the ID current is dynamic by customer system even has no load current. If RDS on over the range of below, what impact will cause by customer system? How to choose right RDS on parameters of MOS? 

              Customer requirement is below and if would like to choose AON6278 or AON6298, which one is suggested? Thank you. 

VIN 12V~48V   IOUT 0~6A

BR

Patrick

  • 0
    TI__Expert 5940 points
    Patrick,

    22mv is the forward regulation point. Using the AON6278, nominal 2.75mohm Rdson will mean that it is in constant regulation mode at the full 6A load on a typical device at 25C. As it warms, it may transition to full gate turn on enhancement. 22mv/6A< Rdson < 100mv/6A is a guideline intended to 1) not waste money on an ultra low Rdson FET that will ge regulated to 22mv regardless, and 2) be much better than a Schottky ORing diode or you will not get the full benefit of the ORing FET circuit. The AO6298 is 31mohm max at temp, so it will be 180mv forward drop. Not enough benefit over a Schottky so I would steer to a lower Rdson. My suggestion would be to go a little higher Rdson than the AO6278, but not much. Maybe a 4 to 5mohm nominal device. I would also match the LM5050's 100v capability with a 100v FET. The AON6278 is only 80v rated. If you can control transients, the AO6278 will work, albeit a little overkill wrt Rdson.

    Brian