LM5050-1-Q1: LM5050-1-Q1 - Is Rg and Rgs for Q1 and Q2 necessary or not?

Hi Gary,

LM5050 is an ORing controller which drives an N-Channel Mosfet in  an orientation (Source - Drain, look at Body Diode orientation) which blocks reverse current when the FET is disabled. LM5050 cannot block forward current as the body diode will be forward biased when Vin is applied.

• For controllers which are intended to block reverse current, we wish to Turn ON and OFF the FET (Q1) as fast as possible. Hence, we do not add any external capacitance on the Gate signal.
• Q2 in LM5050 circuit is used to Enable / Disable the controller and hence a cap on its gate is not required. The reason is similar, you intend to Enable / Disable the controller as soon as possible. 

On the other Hand LM5060 is designed to drive an N-Channel Mosfet in  an orientation (Drain- Source) which blocks forward current when the FET is disabled. 

• For LM5060 a capacitance at gate can be used to slow down the startup and limit the inrush current. This is helpful while starting up into a big output cap. 

Hi Praveen,

Thanks for your support.

If the Rg (gate resistor) and Rgs (gate-source resistor) are the resistor, May I know that the Q1 and Q2 are necessary to add it or not? and How about the LM5060?  Is any suggested value if it is necessary?

Thanks. Gary