Max830CWE chips keep falling over. Help needed

[cchalmers]

Hi, I am having some problems with a Max830CWE DC/DC regulator. I have four of them sitting on my pcb. The problem is that they work ok for maybe a day then they fall over. Their output drops from 3V3 to 0V. For no expicable reason. All the chips have done it at least once. I do have some boards which don't have any problems. I regulate 24V to 3V3. I have checked all the auxilary components (inductors, caps, diode) and they seem fine and as the data sheet says. The current being drawn from the chip is 100mA (well within spec) and I have connected it up exactly as stated. The problem can be cleared with a power cycle. I have a few questions that I would appreciate anyones help with.

1) my input caps are 33uf AVX tants. I shouldn't have any problems with these should I, in terms of oscillation.

2) When I ground the shutdown pin, it recovers for a brief period. Does this ring any bells with people.

3) do you think I have duff parts???? I never think I do cos its now happened on 10 chips.

Your help will be much appreciated

 

[lunatic2]

What are you providing the power for? Are these failing in use in an active circuit? Have you tried using a dummy load to see if they will fail then. How is your output filtered, perhaps a noisy circuit is feeding back into the chip? Bypass caps on any IC's?

 

[Mosfet]

Sounds like it might be getting too hot.
It is supposed to have a thick ground plane below it with heat sink compound.
And large short connections to source and load ground.

 

[cchalmers]

Thanks for your help

Guys,

Thanks for taking the time to reply to my plea. The chips have 66uf tants
on the input, and 300uf tants on the output + 0.1uf ceramic. The passives are all close together and have a nice grounding place. The chip does not get hot to touch at all. Its is only dragging 200mA. I have put a dummy load on the chip but it did not fail, but I only left it for 1 day. I have seen a failure on one board that didn't show for 6 days!!. I will pick a chip that I know fails pretty quickly then load it. I am pretty sure it will go as I actually have 4 max830cwe running on the board and they all fail. They all have different loads (none of which is greater than 200mA).

I know the datasheet states about the thermal compound but the chip isn't running hot and does have thick tracks (a fill) on its ground and input.