Power supply problem

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)

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

Have you looked at the output on a scope?

It's a switching regulator so there will be a high frequency ripple on the output, you need to filter the output, first try a 100nf ceramic capacitor on the output (electrolytics are no good at high frequencies), failing that you need to build a propper filter to remove the ripple.

Failing this, adjust the output of the switcher to a slightly higher voltage, (like 4V) then add a 3.8V ultra low dropout regulator on the output, this configuration is known as a hybrid regulator.

The datasheet implies that the minimum load current to maintain specified regulation is 100mA. I don't know what happens if your load is less than this amount.