Boost LED driver output current problem

[jpou]

Hey all,

I am trying to debug my boost LED driver and would appreciate any help. It is based on MIC2287 and is using reference schematic provided in the datasheet.

This converter is operating with feedback voltage of 90mV. My current sense resistor is 0.39Ω. This should give me output of 230mA. I am using 22µH inductor with 1A current rating.

My problem is that if I connect LED load with Vf=12V it works perfectly and I measure 93mV over the feedback resistor. If I connect LED load with Vf=22V, my output current drops and voltage over current sense resistor is only ~30mV. Unfortunately, I don't have access to scope, so I can't see the duty ratio or other parameters of driver switch.

My converter is powered by 5V PSU.There are 3 ceramic output caps (1 + 1 + 4.7 µF, 50V) and 2 (10+4.7µF) input caps. OVP is removed.

Any help would be highly appreciated!

 

[ea.arun]

one possibility is if the inductor saturation current is 1A for me this design looks on the edge.....
for example for 22V,.23A the output power is 5.06W, and for which the IC internal switch will try to draw 1A current from 5V to achieve the same(power 5.06W or above considering the losses)....
also the inductor value may not be good enough to store enough charge and deliver to the output capacitors....