What is the most elegant way to use the LTC4269-1 with an 30 V auxiliary supply? Take the Demonstration circuit 1335B-C, (DC1335B-C) as your starting point This is a high-power supply featuring the LTC4269IDKD-1, LTC4269-1. I need to plan for the scenario that 30 V could be applied by an auxiliary supply across +VOUT and -VOUT. I know a Schottky diode works, but I can't accept the power loss and heat generated when PoE is in use. I know an ideal diode is an alternative (P-channel MOSFET) but I'd rather not incur the cost. Is there a more elegant way to solve this problem? Is there a condition with this potentially higher voltage on the output that will shut down the part or stop switching the FETs without using the SHDN pin?
I've noticed that the gate for Q2 is max 20 V. It's something to keep in mind for this scenario. What if I replace D14 with a 12 V Zener diode? Would this protect the gate on the secondary MOSFET Q2? Will the LTC4269-1 output regulation stop or go to a very low duty cycle on the SG pin when the 30 V is applied to what would otherwise be a 12 V output?
The data sheet reads, "Auxiliary power can be injected into an LTC4269-1-based PD at the input of the LTC4269-1 VPORTN, at VNEG, or even the power supply output." What did you have in mind for the case when auxiliary power injected at the power supply output? Do we need to use the shutdown (SHDN) pin or can we get away without it?
My calculations and simulations suggest that I can expect a higher Vds across the primary and secondary MOSFETs when I connect 32 V to the +VOUT. On the primary I'm seeing 114 V in simulation and 121 V in calculation. I have selected a Vds of 150 V for both primary and secondary.
Vds1 is the primary MOSFET
Vds2 is the secondary MOSFET
Added question about possibility of shut down without using SHDN pin.
[edited by: current view at 11:45 PM (GMT 0) on 8 Apr 2020]