H bridge Drivers

Look at the functional block diagram for the A4940, on page 3 of the data sheet?

Question: Which is bigger, a ten pound chicken or a ten pound snake?

Answer: that depends on how you define "big".

That's no chicken, that's a turkey ;-) ...Jim Thompson

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Lets say that I wil get both chips to work. Now, what kind of test will let me know that which part is faster?

Thanks John

I haven't had my caffeine yet. I suppose if you buy a five pounder at the supermarket and put the head, feet, feathers and guts back then you'll still not be up to 10 pounds.

(and it'll be a mess).

Or did you mean the snake?

=A0 =A0 =A0...Jim Thompson

Guys, its not a home work. :) .

It's not going to be a 1:1 comparison, mere switching speed isn't the only consideration in a switching supply, and how fast you can get them to work depends a lot on surrounding circuitry. Hence, my comment about the meaning of comparisons.

Each one will have some propagation delay internal to the chip. Each one will have a current source/sink capability that will interact with the drive transistors' gate charge. If either one has anti-shoot through circuitry (I didn't look) then that circuitry will add delay, possibly only under certain circumstances, that will affect your highest attainable speed, possibly in markedly different ways depending on which chip you use.

So what does 'fast' mean to _you_?

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For example if I drive an inductive load by each chip and than by looking at the output voltage waveform across that load. If this ight help than what parameters of the waveform should I be looking at? the slope of the waveform which one is slower or faster.

John

I've never weighed a snake, but I'd guess that a ten pound snake is pretty BIG ;-)

I've killed 2-3 foot rattlers when I lived in the boonies of North Scottsdale. The Dachshunds would grab them behind the head, shake them like crazy, then toss them away... and the other Dachshund would then move in and repeat the trick. So I'd guess the snakes are pretty light weight.

Scared my wife silly. I'd rush in with a hoe and cut their heads off. ...Jim Thompson

Or is half-fast good enough ?:-) ...Jim Thompson

I used to think that my capabilities were vast. Now I find that they're half-vast.

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If you don't understand what you're looking for, you won't even know if you've found it.

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I am looking for which chip will work faster. Now, I do not know what parameter or test will give me the answer. That is why I put this post. If you do not want to answer it its okay but do not make any comment because if someone else want to give me some advice the he/she might not give me the advice because you are replying my post.

thanks John

I hate it when that happens :)

Tim

As has been mentioned before, look at page 3 of the Allegro data sheet.

"Faster" is unspecific. Turning a pair of MOSFETs in an H-bridge on and off has to be looked at as three - hopefully non-overlapping - operations.

1. Turn off the "on" MOSFET

1. Wait until it is off - shoot-through prevention

2. turn on the "off" MOSFET

Turning the MOSFETs on and off involves shifting charge in and out of the gate. The MOSFET data sheet will tell you how much charge, and the driver data sheet will tell you the current available to do the job - both have tolerances.

The anti-shoot-through pause has to cover the turn-off time, plus a margin for the tolerances.

-- Bill Sloman, Nijmegen

"Excuse me sir, has anyone tampered with your luggage without your knowledge?" "If they tampered without my knowledge, how would I know?" "That's why we ask."

Tim

U2? 8*-))