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LM3150: design debuging/layout assistance

Matthew Glazer
Prodigy 20 points
Part Number: LM3150

Hello,

I am working on a design using an LM3150. I've attached schematic/layout and a scope capture below, as well as the webench design report. I'm assuming I have an issue with my layout, but I would like some help before I spin another revision with some changes.

The design is supposed to use a ripple injection circuit and the BOM matches the webench report. However when apply any sort of load, the output regulates up to 7-8V, becomes incredibly noisy and I can hear the regulator. I can reset the regulator only by powering it off completely. What I have found is that the only way the design works is if i completely remove the injection circuit. I get a proper 5V output but there is significant ripple. I'm assuming there's an issue with my layout due to the fact that the switching node is noisy as well. 

I have also tried using the same design with just a Cff cap, and a 68uF instead of 100uF output cap (as per webench) and have similar issues.

Schematic:

Layout:

Scope capture (no injection circuit):

CH1: Vin
CH2: Vout
CH3: SW node

I'm going to remove the ground pour under the inductor and try and shift the FET's and inductor in a bit closer towards the IC to try and shorten trace/pour lengths. I'm also assuming my connection from the switch node to the IC is mediocre and I want to improve that. 

webench_design.pdf

  • 0
    TI__Mastermind 23845 points
    Hi,

    Can you show the location of input capacitor C1, C2,C3,C4,C5, etc? Those input capacitors and the FET should make a tight loop.

    I can see that even without the ripple injection circuit, your switch node seems to oscillate. You can remove the injection circuit as long you have enough ripple at the output. You can try remove all the ceramic output capacitor and use the aluminum electrolytic capacitor with enough ESR to create some ripple.

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Prodigy 20 points

    The silkscreen is hard to see with the copper pours in kicad, here's a better view. I can try an aluminium electrolytic cap I had in the design originally and see what happens. C10 is currently unpopulated in the design. I'll see if that improves the noise on the output at all. Now that you can see where the components actually are, how does the layout look in general? 

    Thanks