I have 2 parallel led string where in each 15 LEDs (350mA, 3.1V).I need to learn from LT3956 700mA 46.5V
But in the end at the exit I 40V 170mA
Please check the CTRL pin voltage. Maybe it is too low and is setting your low current.
Also, check the SW node for stability.
What is the switching frequency?
It seems the matter is that LT3956 limits SW current
Something is wrong.
You have two options.
1.) Get an LT3956 demonstration circuit and use that.
2.) Start debugging this on the oscilloscope. Check the SW node waveform for stability.
Also, check the output voltage so that Vfb is not hitting 1.2V. It should be below 1.1V.
Have you considered running at a lower switching frequency with a larger inductor?1MHz switching frequency is not recommended for your duty cycle and power output.
400kHz is a good fit.
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