I have moved this customer request from the feedback system to this forum.
The original customer question was:
"I have designed a circuit using the Power Designer webpage on the National Semiconductor website using the LM3150MHE and when it was built, the voltage output was much less than what the designer said it would be.
Is there some reason why this would happen?
Would the layout have this much of an effect?
If it does, is there a way to improve it?"
"We received your questions on your LM3150 WEBENCH design. Can you please send us scope shots of board, share the schematic, and share the layout for an applications engineer to comment?
I guess you are taking care of this.
This is a follow up to close off this post.
Additional information was provided. This included a layout. The question was posed as to whether the PCB layout affects performance. My response is below.
Yes the layout is important. I recommend the customer get an eval board and place all of their components on that to see proper operation.
Problems with the layout. There are several but the most important is as follows
1) There is a very large ac current in this ground trace from CIN1 to M2. This is going to place a considerable amount of noise on the aground pin of the LM3150 which is also connected to this trace. This by itself can cause problems in just about every circuit shown because it is the bypassing for Soft start, Vcc, FB, etc…
Cin should be moved so that it bypasses M1 (Vin) and M2 (Gnd)
A fill of ground copper should be used on the bottom metal to reduce the inductance.
Here is a recap of the datasheet with further suggestions
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