LMR14050: Repeated failure of LMR14050 ICs

Hi Chris,

The prototype you built has too high stray inductance on switching current path which may cause ringing or spike over 40V to damage the IC, the board may works with linear regulator, but almost no chance to work with switching regulator. I strongly suggest you to apply LMR14050 EVM and modify the circuit to your application. 

B R

Andy

Hi Andy,

I greatly appreciate your help with this! As you can probably tell, I'm a beginner.

I've laid out the PCB attached below. Can you see any obvious issues? Do you expect that this would work at full load?

Many thanks,
Chris.

Hi Chris,

Do you have requirement on switching frequency and ambient temperature? 

The Webench shows the IC power loss is 2.7W at 4A load current, for theta_JA=40C,  it will cause about 108C temp increase over ambient temp!!

B R

Andy

Hi Andy,

The ambient could be as high as 50C. This was an input parameter in Webench and it proposed the design shown in the first post.

By my calcs 2.8W  x  26.0 degC/W = 72.8C
IC @ 72.8C + Ambient @ 50C = Max temp 123C

Is the above correct? If so I think it's borderline OK? Borderline would be acceptable for this application as it will only be used intermittently and typically at less than full load.

There is no requirement for switching frequency.

Thanks again,
Chris.

Hi Chris,

What's the PCB layers and copper foil thickness you will use? and how about PCB size?

B R

Andy

Hi Andy,

Many thanks for reviewing this. PCB details below:

• Layers: 2
• Board thickness: 1.6mm
• Copper thickness: 1oz / 1.4mils
• Width: 150mm
• Height: 205mm

Detailed PCB pdf attached.

Cheers,
Chris.

Design2.pdf

Hi Chris,

I don't think your PCB thermal performance can be lower as 26C/W which require 4 layer PCB with 2 Oz copper. 

You may go ahead with below PCB design changes, pls add 6 vias on LMR14050 pad as described on data sheet. 

Many thanks Andy, I greatly appreciate your help with this!

I'll make the changes suggested and see how it goes.

Cheers,
Chris.