I’m looking for insight into some problems I’m having regarding the current waveform of an LT3956 LED driver. The circuit is very similar to the buck-boost application from the datasheet (page 17). The screenshot below shows the application with the updated values I’m using.
As is detailed in the photo,
Vin = 12v
SW frequency = 300kHz
Vled ~ 3.3v
The scope screenshots show the LED being driven at 100mA @ 8%.
Blue – Current (inductor and diode respectivly)
Brown – Switch node voltage
Red – Vout voltage
The charging and discharging of the inductor current as well as the diode current are both inconsistent with the expected behavior. My first thought was that the diode wasn’t switching quickly enough. I replaced the diode called out in the datasheet (MBRS3100T3) with a fast switching diode (MBRS4201T3G). This didn’t improve anything. I have verified that the control pin voltage, PWM output voltage, and feedback pin voltage are all operating as expected.
Any help is greatly appreciated.