Strange Bridge Controll issues(again)


So I increased the speed of the PWM to 60khz and it worked... at least for a few seconds. It seems if it was too low of a speed then the IC's(MAX5063) would burn up because I guess they would try to drive the highside gates without a good reference voltage.

But now I'm driving it at 60khz and I think the mosfets are burning up(or at least getting hot... I do not know what is happening to the drivers). Even when driving a small motor the fets get warm(not much actually but probably shouldn't even change temp) to the touch.

But mosfets use more power the faster the switch! So how the heck am I suppose to choose the optimal pwm frequency that provides the MAX5063 with a stable boost and minimize the fet switching power losses?

Nothing in the datasheet discusses the pwm speed(which is why I initially did it at about 100hz for testing which only worked for driving led's).

The's damn ic's are driving me nuts ;/ at $4 a pop I think I'm just going to go with dual drivers and dual powerfets. (would be about the same prive and much easier to work with giving all the problems I'm having with the MAX's(they could at least have some overload protection)).

What I was noticing when I ran it at < 1khz was that about a duty cycle of

75% the motor would stutter(like it would stall). I have no idea what's causing this but I'm thinking one of the max's is bad or possibly the power fets.

I can't believe this damn thing is causing so many problems ;/

(for those who don't remember or haven't been following...

What I have is a pic24 generating a pwm signal. It goes into some logic that takes the 2 input's and generates 4 outputs that represent states of the fets. Basically toggling one side's high and low for the boost generation and locking the other side properly... one of the input's completely flips everything so it can be ran "backwards".

Everything works up until this point. I get problems when going into the max chips(which simply take the output's of the logic as input's).

The circuit is extremely simple

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Now that I think about it, the fets could be getting warm due to "shoot-through" since I'm not delaying the signals but I imagine the transitions on the logic are just fine. I don't recall the fets getting warm when using a small load(led's) so it seems to be load dependent which would point to a different problem.

Surely 60khz is just fine and shoudln't cause the IC's to screw up? (with maybe a 0.5A load.. the fets are rated at 40A)

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Jon Slaughter
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