Hi,
I know many posts were answered about noisy outputs on the LM3478. The answers were talking about the Over Voltage Protection and solutions were proposed. I'v tried many of those solutions but there is still a little bit noise at the outputs depending th load current.
Here's a description of my project.
I'm using the LM3478 in a product that will be use in cars. So the input voltage should be between 9VDC and 32VDC (for 24V car system). The typical input voltage should be around 13-14VDC. The LM3478 is supplying LEDs that are controlled by PWM so it is not a conitnuous load. There is a smal continuous load (UI switch/button LED around 10mA) The load can vary from 50mA to 1A depending on the number of LEDs we are controlling.
Here is the schematic of the switcher of my product:
I add 1uF and 100nF ceramic capacitors at the output voltage ( || to C26). Also I've tried to increase C26 capacitors to 1mF. It helps a lot but I still have noise at some point when I changed the load. Also I've tried to increase the inductors without success. Maybe I should modify the Ccomp and Rcomp values but I don't know what value to use.
The facts that the load circuit is not steady and changed, I can't use the WeBench simulations to get all the parts values because it changes depending if I have a load of 100mA or a load of 1A.
Here are few scope screenshots I made of the output voltage in AC mode:
On the image below the load was around 80mA.
On the image below the load was about 100mA.
On the image below the load was about 150mA
Regards,
