I am using LT3748 for PoE supply generation.
Below is my circuit:
I am testing this circuit.
I am not getting any output.
Is any wrong connection to INTVCC pin?
INTVCC is generated internally, so I do not understand why you connect your input voltage via the resistive divider towards INTVCC. As first step you might remove the two resistors.
I cannot see/extract any component values due to low resolution.
What is the GATE doing?
How large is your gate resistor?
Thanks for response.
Actually there was a mistake in my schematic previously(INTVCC is directly connected to 48V_VIN).
Whether knowing about that I turned on the supply and the MOSFET was getting damaged every time.
To resolve that issue I cut the trace between INTVCC to 48V_VIN and placed a new MOSFET) then I have applied the voltage MOSFET was safe but I was not getting any voltage on INTVCC resulting not turning the MOSFET ON.
I have changed the IC too but It won't work.
After that I have followed page no 18-19 of LTC3748 datasheet.
Which states three configurations of INTVCC pin from which first is not worked for me therefore I went to 3rd method.
I have used 39K & 6.8K for resistor divider network to provide 7.19V.(VIN=48V)
After giving this also I was not getting output. I don't know what was damaged in my board.
I have used a new board and first cut the connection between INTVCC and 48V_VIN then tested and it worked.
I have added a few changes to protect the MOSFET. I have put 100K pull down at gate pin of MOSFET as well as used a zener between SOURCE & GATE pin of MOSFET(If it is not implemented then at the time of EN=0V, I was still getting 1V at output which should be zero).
I haven't provided anything to INTVCC ,I am getting 7.04V at this pin and receiving the output too.
But the GATE to GND voltage is 90mV which should be INTVCC-0.05V that is strange for me .
Will you give me any answer for this?
Waiting for reply.
Thanks & regards
so you get INTVCC according to the datasheet value and outpuit voltage=48V as desired?
LT3748 has to switch if any load is to be delivered. And is has to switch for startup to charge up .output capacitors towards 48V.
Any scope shots from your main voltages?
you know, that LT3748 is a 'switching' regulator, hence gate voltage should be some kind of pulse train?
And LT3748 does need some kind of minimum load to offer stable regulation. This is stated in the datasheet. So the difference of 47V (loaded) and 53V (unloaded) is aligned with expected behaviour.
i suggest to use LTSpice to check and understand your circuit more in detail