Power supply problem

[Guest]

Does anyone have any idea why this power supply circuit (attached) glitches when running at 24v input and 3.8v output, it supplies a GSM (max pulse 2.5A)

www.myproblem.pwp.blueyonder.co.uk/LM2676SADJ.jpg


I think it's when it draws a high current as I can watch the AT commands but then they just stop.

It works fine at 12v

The glitch causes my project to reset

Thanks

[rwyoung]

First guess would be that your output bypass caps are insufficient. Insufficient with respect to ESR, capacity and location. Also, how did you run your grounds? Point-to-point, plane, or star? For a high current load you should consider a star-ground, a single, fat trace from the point of load directly back to the ground of the supply IC.

Since this is a National Semi part, you can simulate on their web site. I think you can simulate transient loads. Do that and read carefully their instructions and advice about bypassing, capacitor selection and grounding.
_________________
Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month!

[jecottrell]

Look at Fig. 6, on p. 15 of the data sheet. A 24V input suggests a 47uH inductor....

Good luck,

John