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Exploding IC in buck converter
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Teun:
Hi guys,

I have an interesting problem.
A client of ours has sent back several buck converters we supply. Never had much trouble with them espescially for this client.

It is used to charge a mobile device with an onboard receipt printer. These are used on busses for public transport.

Over time most of the PCB's have blown IC's. All on the side of the input pin.(see picture) TVS and varistors are used to handle spikes on the input. The converter should be able to deliver 9V/3A (IC rated 6A output) on the output and from what i can see with the printer activated it uses 28W of power max. The current limit/OCP of the converter is set to 3.5A.

Input range is +/-   12-32V DC. (Busses can be around 30VDC)

Can anyone give me an idea of why the input would be blown?
Ian.M:
Automotive DC supply transients are *NASTY* especially on older or poorly maintained vehicles.  Probably you haven't got enough headroom between the TVS and varistor clamping voltage during a high energy transient spike and the abs.max. input voltage of the IC.   Post a schematic for your input protection circuit, + links to datasheets for the IC, TVS and varistor.
Hast:
Hi

I have had a similar problem.
I did a buck converter for a industrial system with "industrial 24V".
At first everything worked fine and then we started to get returns where the input was blown similar to yours.

After some measuring we found that the "industrial 24V" was a strange sinusoidal signal from 0-48V. The buck converter I used had a max of around 32 V in or something like that.
The customer had switched out the 24V supply to a cheaper one.

So measure the input voltage with an oscilloscope and not a multimeter is my advice.

BR
max_torque:
Load Dump for 24v nominal systems is speced at 212 volts!   What LD and RBP (Reverse Battery Protection) do you have in place in this unit!
T3sl4co1l:
Hmm, that's exactly where the bondwire ought to be, too.  That thing ate a lot of amperes, very quickly. :-DD

Yeah, 30V, useless.  What knucklehead designed this thing?  To what standards was it tested?

Automotive parts start at 50V and go up from there, and that's mainly for 12V systems with modest (70A) alternators.  You might want an 80V rating here for example, just so there's enough headroom to handle the transients how ever you can (probably by disconnecting the load?).

Tim
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