Battery causes device failure

I have a circuit(an Hbridge) that I run off my bench supply. It draws <

100ma(actually about 10ma on average) but when I hook up a battery it causes the ic's to fail ;/

The bench supply is almost 12V while the battery is almost 13V(about 1V higher) the chips have a max rating of about 12.6 volts and the battery is just a few 100mV higher. (it was reading ~12.7V with no load)

In any case when hook the positive up it sparks but doesn't do it on the bench supply.

It makes no sense why the battery would do this as there is no direct short(although it could be a startup issue where the mosfets in the hbridge end up shorting momentarily which somehow destroys the POS IC's).

Basically I'm replacing the bench supply with the battery(a car battery) and it ruins the device yet works fine with the bench. (the bench is basically a LM317 regulator) As I said, the only thing that is different is the voltage being a little higher on the battery and barely going over the max voltage of the device(which I would imagine wouldn't cause a catastrophic failure).

Any ideas?

Reply to
Jon Slaughter
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Why would you imagine that? It is not suitable to operate any device @ the MAX ratings, much less above them. By battery, do you mean that you put it in a car and it fried? It is not uncommon to see the voltage constantly above 14.7V in a car. There are other times (google up load dump) that a device in a car may see more than 50V for short periods.

Reply to
Anthony Fremont

Well, the spec says 15V absolute max and average max is 12.6V so I imagine it's fine. No, it was a car battery... not a car.

Reply to
Jon Slaughter

I suspect your circuit briefly draws an excessive current pulse. The car battery will happily supply 100 amps. Amps or tens of amps for only microseconds could be enough to destroy a chip.

Reply to
Andrew Holme

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You probably have too much resistance in your hook-up wires to draw really large currents; but just a few amps could be enough.

Reply to
Andrew Holme

You probably have too much resistance in your hook-up wires to draw really large currents; but just a few amps could be enough.

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yeah.. the IC\'s are only rated for up to 2 amps and I did blow a mosfet ;/ I 
guess the mosfets are floating at startup before the IC powers up and pulls 
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Reply to
Jon Slaughter

Looks like some kind of latch-up to me. Probably the bench supply limits the current enough to avoid it. What kind of chip is it that always blows and what's hanging on the other end of it?

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Regards, Joerg

http://www.analogconsultants.com/
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Reply to
Joerg

Yesterday I designed a half-bridge switcher, another one coming tomorrow. You need to maintain sane start-up conditions. I have current limiting feedback in there, otherwise these thing try really, really hard to get the voltage up at the other end. If the bench supply is a LM317, well, it won't allow it to draw umpteen amps. A car battery does and then ... phsssst ... *BANG*

--
Regards, Joerg

http://www.analogconsultants.com/
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Reply to
Joerg

In cold conditions, try 15.3V nominal, with transients of several hundred volts ;-)

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

My guess is you have something incorrect in the circuit that is momentarily shorting on start up. The LM317 is only a little pony regulator and would simply fold back. The battery on the other hand how ever, will not give up so easily.

I doubt if initial arching is causing that much damage when connecting the battery how ever, you could try a TVS unidirectional diode across the rails. This will clamp any thing over the selected rating of the diode and kill reverse transients.

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Reply to
Jamie

When it was cold I usually had zero volts in my Citroen. But ah! I had a stack of four D-cells soldered together. That made the cranking process a lot easier. Chugga, chugga, chugga ... *BANG* ... vroooom. Sometimes I had to wipe the soot off the bumper of the car behind mine. One time the

2nd muffler pot flew off and rolled down the street. But I caught it in time.
--
Regards, Joerg

http://www.analogconsultants.com/
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Reply to
Joerg

Back in my automotive electronics days the operating voltage range spec was +4V to +18V, with the requirement to withstand "load dump" AND negative current flow of 20Amps :-(

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Most likely it is the initial state that is causing the problem. I guess what happens, and htis is just a guess, is that one or both sides of the hbridge are shorting out and the IC tries to raise the voltage to turn them off but because there is so much current it has an extremely low voltage and it can't turn off the mosfet so it pumps more current trying to turn it off and it can't.

The IC is a Max5063A. These things seem to die left and right when they are around me.... if I just look at them they explode.

(don't understand why, at $4 a pop there can't be any type of protection circuitry)

Reply to
Jon Slaughter

Well, that is probably it but I'm not sure how to get around it... I can't use a regulator(I can but I don't want to waste power since it's battery powered).

I'm going to try to add some pulldowns hoping that it will work... although not quite sure what resistance to use... to little just wastes power but to much might not solve the problem(I guess I'll have to play around with)... running out of IC's though ;/

I guess what I can do is add the pulldowns, remove the ic's, and then try the battery... if it shorts then it's not the ic's. If it doesn't, then it's the ic's ;)

Reply to
Jon Slaughter

Look thru the data sheet for some initialization method... everything OFF until Q-point reached.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Post your schematic.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

soft start circuit that supply's the bridge.

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Reply to
Jamie

I was just going to say that. And if taking the IC out means some floating FET gates then all bets are off. That could result in the ultimate kablouie. One where the fire extinguisher has to come on scene ;-)

--
Regards, Joerg

http://www.analogconsultants.com/
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Reply to
Joerg

Well, I never use those high-faluting high-voltage bootstrap things. I use transformers and then regular (a.k.a. cheap) drivers.

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Regards, Joerg

http://www.analogconsultants.com/
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Reply to
Joerg

The OP talks of 12.6V, which I interpret as the driver power, but wonder what he has for the FET's ???

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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