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Question about SN754410 and current capability

As the SN754410 H-bridge driver is rated at 1A, am I correct in thinking that it can handle 1A at the max voltage of 36V and therefor will be able to handle 3A @ 12V and 6A @ 6V ?

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When the internal transistors turn on their voltage drop remains reasonably constant regardless of the supply voltage. No matter if you use 6V or 36V the difference in voltage is across your motor where it should be, not the H bridge. If you look at a data sheet for any transistor and look at the value given for Vce(sat) it is usually less than 1V and it's value depends on collector current, not supply voltage.

I would imagine the limitation is due to the transistors or FETs that are used on the IC.

I also agree it is likely a limitation of the interconnects used in the IC, similar to how a trace width on a PCB can only handle so much current.

No, the SN754410 can handle 1A continuous and 2A peak (for a very short time) per motor regardless of voltage. But you can stack up chips to get more amperage, however, it's a good idea to stick some heat sink between them. Here is a picture of what I'm talking about:

That’s the part I don’t understand.
1A @ 36V should be 36W and 6A @ 6V is also 36W. Isn’t the limitation of the chip based on the energy that it can handle in terms of Watt?
Isn’t 1A at 36V completely different from 1A at 6V?

I will just add to the confusion. If one reads the datasheet it says maximum continuous power rating is 2075mW or 2.075W.

That would seem to imply if you run 6v motors then you have a maximum of 345mA to stay within the power limit and at 36v only 57mA.

What I was surprised to see in comparison with the L293D is it has a power rating of 5W. Interesting. It is a good question you have asked.

I recommend using the L298. Very good IC - 2 channels, handles up to 2A per channel or 4amps if setup to use one channel. Has temperature and current monitoring and costs around $3. 25W power rating but can handle a fair amount more with a good heatsink because it has such a large ground plane. Only drawback is non-standard 0.1mm pitch for DIP package.

Isn’t 1A at 36V completely different from 1A at 6V?
Yes it is. In the former case your chip will be really hot and running close to it's maximum spec. In the latter case you will be running well within tolerable limits.

"...it can handle 1A at the max voltage of 36V and therefor will be able to handle 3A @ 12V and 6A @ 6V ?"
No, while those represent the same power, they do not represent the same physical occurance. With more amps you have more electrons moving with less energy each. With less amps you have less electrons moving with more energy each.

In general the maximum voltage and current will represent the maximum electrical characteristics of your device. These warn you when parts traces will burn. The power is a measure of how much heat it can dissipate. So you need to make certain you stay within all spec to stop the part from frying.