# Ground as Heat Sink

First of all, this might be a newbie question, but I'm just getting into hobby electronics and robotics, so this is all very new to me. Anyways, I'm looking at the data-sheet for an L293 IC, which shows some of the pins as "heat sink and ground". Does this mean I should avoid using this IC on breadboards, or is it something I don't need to worry about? Should I add a heat sink to the IC to further reduce heat issues, or does the pin heat sinks do the job fine? The IC is going act as a H-Bridge and run motors with the following characteristics:

Voltage             =  12 V
Normal Load Current = 120 mA
Stall Current       = 360 mA


In case you think the IC is a bad choice, I should let you know that electronic components aren't easily accessible where I live, which means I take the closest I can get.

Datasheet clearly says, that maximum 'freeair'(breadboard case) power dissipation is ~1.5-2W. At 360mA, and 1.8V maximum voltage drop inside chip, you are dissipating 0.648W per channel.

So, if you will have 3 or 4 channels in high state, you are exceeding your maximum power budget.

While reaching this is probably not very likely (all channels connected to stall motors), but if you want to be safe, add some heatsink to this chip, and you'll be fine even on breadboard.

• Marking this the correct, however, all the other answers are relevant, so if you have a similar question, take a look at them as well. – William Mariager Jun 22 '11 at 14:17

I don't know much about motor drivers but we used a similar IC for a project and drew a lot of current (at 7.4V), maybe even more than your stall current for a majority of the time. We used three of these motor drivers simultaneously. We had them on a breadboard before we moved to a PCB and everything seemed to work fine although the chips did get very warm. We didn't have any heat sink near those ground pins either. I think you'll be okay but if you can add a heat sink I would.

With regards to what dhsieh said, they got really warm. If you touched them unexpectedly it was hot enough to startle you. Factor in the fact that we were running at or below 7.4V as or battery drained and I would be a little worried about touching them when running at 12V.

That said on page 7 of the datasheet they show some application information which indicates a thermal shutdown inside the IC. I'm guessing you'll be fine to try it and the chip will just shutdown if it get's too hot, then you'll know you need a heatsink.

But like I said above, be careful touching it.

I think that would be that they can be connected to ground and a heatsink. Since they save some pins in the centre it looks like they like to "clip on" a heatsink over those pins that press down on the IC. Not that those pins would act as heat dissipation.

So if the chip needs a sink, you need to press one on there since those pins will probably not affect the heat at all.

Apparently those chips has thick internal copper connections that can lead the heat out from the chipcore so they are a little bit better than the ones that dont have that feature.

And normally you would put paste on top of the chip and then press the sink down, but in this case it sounds like it is more important that the sink is connected to those magic pins.

• The reason for placing these pins in the center is that they're closest to the die that way, and that the thermal resistance to the PCB's copper is the lowest. – stevenvh Jun 22 '11 at 6:16
• Good point, so maybe they can affect a little. – Johan Jun 22 '11 at 6:23
• Heatsink pins are most definitely effective. I've designed some boards with A3977 stepper driver ICs, which have three heatsink pins per side. These pins are connected to large coper pours on the PCB, and the copper pours definitely warm up considerably when the thing is in operation. – Connor Wolf Jun 22 '11 at 7:45
• Good point, so maybe they can affect a little bit more... – Johan Jun 22 '11 at 7:56
• As an extra to a large copper pour, using 70$\mu$ copper instead of the standard 35$\mu$ also helps considerably in draining the heat away from the IC. – stevenvh Jun 22 '11 at 8:08