I purchased a DC2345A evaluation board for the LT8391A. I modified the board to output 40V by changing R6 to 25KOhms and 5.5A by modifying the sense resistor to 18 mOhms. This works great when running the LEDs at 100% duty cycle.
However, when PWM dimming is introduced (internal or external) the lights flash at 7 Hz with modulation active while the lights are actually on during each of the 7 times per second. It seems like there is another component which needs swapping, but I need some help looking in the right direction of what to change.
Things I've tried:
Any input is greatly appreciated! I know the chip is capable of this load so it has to be some of the circuits around it. I have already began a PCB design but really need to prove this out on the bench before getting it manufactured. Thanks in advance!
Looking further, I'm suspecting this is a result of the power stages since the "equilibrum" during the off time is right around 25 V which is what the kit was designed to work with. Any experts who can chime in and confirm?
Please re-check your computations for the Rsense resistor. 18 mOhms is higher than what I expect to be used in this configuration.
Thank you for the response. The calculation I performed was Rsense = 100mV / 5.56 A since CTRL1/2 are both at VREF. The output current is perfect when the PWM is 100%. It is only when dimming is introduced there is an issue. The Rsense value is for R1 on the output. The input Rsense is unmodified.
My gut is telling me the inductor needs attention as it was getting up to around 250F and the output current is significantly higher than the original design.
You would indeed need to increase the its size if your inductor is reaching that temperature.