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Tireless search for a small 5A H-Bridge

Catwell
I need a small H-bridge option, similar to this Maxim 1A H-Bridge IC, but could handle at least 4A, ideally 5A. It doesn't have to be in a 8-SOIC package, but I do not want a 2"x2" PCB version either. A single chip would be best.
 
Thoughts?
 
This will be for a stepper/servo motor driver, ultimately.
 
Cabe
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    Ok, 5A for a full bridge isn't going to be easy to find in a single chip. You're looking at i2r losses of 5W for .1 ohm fets and 500mW for .01 ohm fets That means you are looking at D9 packages at the minimum for discrete FETs (no SOT23's will carry that much current and not desolder themselves). The typical TO-220AB package will dissipate 2.5W in free air. I wrote up a tutorial on h-bridges here http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/index.html and will follow up with a FET version here now that I've got stuff worked out on the web site (new site will be http://robotics.mcmanis.com)

     

    The way to look at this is what the Rds(on) value is for the FET, then square the current and multiply that by 2 (high side fet and low side fet) that is the power that has to be dissipated by the package. If the temperature goes up (which it will do without a heat sink) then Rds goes up too (which means more power gets dissipated) Good general rule of thumb is that Rds(on) doubles at max temperature. So if the data sheet says it has a 1 milliohm Rds(on) then at full temp that will be 2 milliohms. On steppers you probably want a good chopper drive anyway to get maximum torque out of them.

     

    ---Chuck

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    Ok, 5A for a full bridge isn't going to be easy to find in a single chip. You're looking at i2r losses of 5W for .1 ohm fets and 500mW for .01 ohm fets That means you are looking at D9 packages at the minimum for discrete FETs (no SOT23's will carry that much current and not desolder themselves). The typical TO-220AB package will dissipate 2.5W in free air. I wrote up a tutorial on h-bridges here http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/index.html and will follow up with a FET version here now that I've got stuff worked out on the web site (new site will be http://robotics.mcmanis.com)

     

    The way to look at this is what the Rds(on) value is for the FET, then square the current and multiply that by 2 (high side fet and low side fet) that is the power that has to be dissipated by the package. If the temperature goes up (which it will do without a heat sink) then Rds goes up too (which means more power gets dissipated) Good general rule of thumb is that Rds(on) doubles at max temperature. So if the data sheet says it has a 1 milliohm Rds(on) then at full temp that will be 2 milliohms. On steppers you probably want a good chopper drive anyway to get maximum torque out of them.

     

    ---Chuck

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