(Active Rectifier Controller)How to chose FET.

Question

Hi 
 I have a question about an "Active Rectifier Controller" such as the LT8672. I think it depends on the device, but I think it regulates the VDS to 20 mV or 30 mV when the current flows. I think that the regulation itself is controlled by VGS, but I think that no matter how much the gate voltage is driven, a drop of the on-resistance of the FET will occur. This is also stated in the data sheet, and I don't think there is any particular problem. 
 On the other hand, when using these Active Rectifier Controllers, if we want to maintain the regulation voltage even at the maximum value of the assumed current load, you we to select one with a sufficiently low on-resistance. For example, if we choose a 6m&Omega; FET and the regulation voltage of the ideal diode controller is 30mV, we can use up to 5A. Conversely, if we want to drive up to 10A within the regulation range, I think we need to choose a FET that does not have 3m&Omega;. Is my understanding correct? 
 Best regards Kawa

RDSmith · Accepted Answer

The output current and voltage regulation gives the upper bound for on-state resistance if you want to remain in active mode. However, if you are fine with extra power dissipation, you can use a FET with an even higher Rdson value; the part will simply drive the part into saturation in an attempt to keep the voltage drop down to the 30mV level. At that point it becomes an issue of thermal sinking. You could use a 50mohm part at 10A if you can somehow keep it cool enough. However, the PG pin will assert if the voltage drop increases beyond 75mV (typ))

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(Active Rectifier Controller)How to chose FET.