LTC3803 isolated DC/DC

Question

I designed PoE power supply with using LTC3803, and it's work fine in non-isolated variant, but i have problems with isolated variant. 
 Schematic of isolated variant: 
 It doesn't work the way I want it to. By changing resistors R41 and R43, I cannot set more than 4V, but I need 5V. I simulated it in LTspice and everything works fine. Maybe you know why it doesn't work?

Fil · Accepted Answer

Hi, 
 The problem may be with feedback circuit TLV431. We don&rsquo;t know if that circuit will work or what the problem is. We recommend using LT4430 for feedback as shown on page 13 of LTC3803 datasheet.)

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LTC3803 isolated DC/DC