MP3398A Question

I have a prototype board made here using the MP3398A as a boost converter for 4 strings, 7 led’s 2.9 forward voltage per LED at 350mA. Vin is 12V and I am measuring 20V at Vout which is good. However, with ADIM and PWM high (100% duty cycle) I am only measuring .034A going in and out of the LED strings which is about 10% of what I would expect. Additionally with low duty cycles the current is even lower and the LEDs are flickering but the voltage appears to remain okay at 20V on Vout… Any thoughts on why this may be?

Mike D.

Use a regular old DC power supply to characterize your load. How much Vout do you need to get 350mA.

Also the current sense resistor is returned to signal ground I think is a mistake that is a high current path and it should return to power ground.

Thank you for the reply -
I did make that change on the current sense resistor, i noticed on the Evaluation board it looks like VCC is also tied to PGND as well.

As for the required Vout i did measure at .350mA i need 20.50V per string which lines up with what i was getting on the prototype board.