LM3150: Higher load

Joel Findley

Part Number: LM3150

I'm testing my 3.3V 10A buck regulator that uses the LM3150 and I noticed that my High Side Gate signal looks good up to 5A than i starts to have a small dip/drop during he cycle, see screen shots below. Any guidance as due to the cause would be great. The 1st picutre is a screen shot of the gate signal below 5A. The second 2 are different gate signals oveserved above 5A.

over 6 years ago

0 Arief Hernadi over 6 years ago

TI__Mastermind 23835 points

Hi,

Do you have a picture of your layout? It is important to keep the input capacitor loop and the 2 FETs small enough.
Also make sure that your design does not hit current limit set by the RLIMIT.

Thanks
-Arief

0 Joel Findley over 6 years ago in reply to Arief Hernadi

Prodigy 100 points

Here is an image of my schmatic and layout, I don't belive i'm hitting a current limit as I have R2_1 (I_lim resistor) currently not populated.

0 Joel Findley over 6 years ago in reply to Joel Findley

Prodigy 100 points

Was this helpful?

0 Arief Hernadi over 6 years ago in reply to Joel Findley

TI__Mastermind 23835 points

Hi,

Have you try to add more capacitor at the output just like the EVM?
www.ti.com/.../snva371d.pdf

Thanks
-Arief

0 Joel Findley over 6 years ago in reply to Arief Hernadi

Prodigy 100 points

I have 300uf on the output, I have a mistake in my part information in altium, My calculations show that I need a minimum of 220uf I would assume I have enough on the output.

0 Joel Findley over 6 years ago in reply to Joel Findley

Prodigy 100 points

I'm looking at the Alternate ripple injection section of AN-1900 how do you caclulate the vaules of Rr,Cr and Cac? When I add anything to this node or to Cff the ouput no longer regulates to 3.3V using the resistor values found using Vout=Vfb x (Rfb1+Rfb2)/Rfb1.

0 Arief Hernadi over 6 years ago in reply to Joel Findley

TI__Mastermind 23835 points

Hi,

I normally follow this equations for calculating the Ripple injection portion of it

Thanks

-Arief

0 Joel Findley over 6 years ago in reply to Arief Hernadi

Prodigy 100 points

I used the formulas found in the referenced materials and I still have a stability issue, when I add Rr=10k, Cr=.01uf and Cac=0.22uf it changes my output voltage from 3.3V to 4.5 - 4.8V (not stable) as well as the switching frequency goes from 300kHz to 430kHz. I didn't see any of this during my initial testing with a resistive load, I then moved it to power my PCB and saw that my upper FET was at 140°C after 10 minutes and started to probe with a scope. I now have the instability issue with a resistive load also, is there a chance the IC is damaged?

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LM3150: Higher load