I'm using the following circuit to drive the backlight LEDs of an TFT LCD module:
Please note that the input voltage was changed to 3.3V from 5V (should not matter).
The FB pin is supposed to be regulated to 300mV so the current delivered to the LEDs is given by i = 0.3 / R
Since the LCD datasheet mentioned a max current of 27.5mA I've decided to go with the 11 Ohm resistor which limits the current to just a bit under that.
The driver datasheet mentioned it can drive up to 5 LEDs in series. Recommended max voltage is 24V. The LCD actually has 6 LEDs with a suggested max. voltage of about 21V so I figure that although there are 6 LEDs, electrically this seems to be all within spec.
When turning on the device (with SHDN on high) I get the LCDs going + current draw adds another 400mA and power supply goes into standby.
Is there anything that can be wrong in this part of the circuit or should I look for the faults elsewhere?