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Re: Smokin' gate drive chips on DRSSTC-2 board

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Dan,

Sometimes the designers of those chips get so exited about running super fast high current stuff that they forget the open load case... It is not easy designing those chips and they get all tunnel visioned on the final goal rather than the folks "playing" with the chips ;-)) Not a problem since 99.99% of the time they are not open load ;-) But when we are "goofing" with them...

I forget what the exact thing is, but the driver gates need to be discharged... Open load does not let that happen before the other side cranks on and the power supplies start "singing" or something... I don't think it is a bypass cap thing though, but it was on the inside of the chip...

In my case, the two chips are in parallel (low side)and one was happy and the other was going nuclear... It just depends on the chip the weather that day.

But no problem at all. We just need to load them with like a 100 ohm resistor or something when we are messing with the boards alone. An added resistor to the board might fix that too if you want to make it bullet proof. But a minor thing in the long run ;-))

I think you have to call the chip maker and quiz them for things they forget to put in the data sheets about running them open load to get all the gory details... We ran into it on a bare board manufacturing test.... I think they just added a 1 cent resistor to the board that was a "don't care" while running in the final machine, but fixed the board test failures. The final thing was just "don't run them open load". Like a radio transmitter, it just blows it up... It was a first meeting of the day thing and I was mostly asleep ;-))

Cheers,

        Terry


At 01:44 PM 12/5/2004, you wrote: 
I don't see how running these gate drivers without a load could cause any
problems whatsoever.

Dan


> >I am building (3) of Dan McCauley's DRSSTC driver boards, and the first
one
> >I powered up (with no gate drive transformer connected) instantly let out
a
> >small wisp of smoke from one of the driver chips  ......
>
> I see.  I bet they need a load to run right.