L293D maximum current with heatsink

I saw in datasheet of L293D that maximum current per channel is 650mA. I have two dc motors that draw within that limitation. Most of the time, measured current is around 1.1A (sum for both motors). Under heavier load it could probably rise few hundreds of mA.

With usage of heatsink would that limitation be extended ? Am i on the safe side ?

• Do you have a datasheet? – jippie Mar 20 '13 at 9:15
• I have included it, now. – Gossamer Mar 20 '13 at 9:28
• How do you intend attaching the heatsink? I've heard of people gluing Al to DIL chips, but I don't think that it worked very well. – Leon Heller Mar 20 '13 at 10:07
• L293D is capable to run 22V Motor? – user52159 Sep 10 '14 at 4:51

Exceeding the ratings continuously is not a good idea. The part will fail. And possibly catch fire (I am not kidding). A heat sink will not improve things by much on a plastic DIL. The junction isn't thermally connected well enough to the case to bring the heat that far, even if you do manage to firmly attach a heatsink to the surface.

However, you seem to be fairly close to the limit, and you claim to have a bagful of L293s lying around. You can simply use multiple channels in parallel (one chip per motor instead of half chip per motor). This should be enough to keep things within the acceptable limits.

The L293D can have multiple channels connected in parallel. This is not a generally applicable approach, though. Don't try this with, say 7805s or LDOs without first considering the consequences. Power regulation ICs which allow this will have mention of it in the datasheet as load balancing. However, the L293D is not strictly a power regulating IC, and your load is fairly specific (a motor). There will be minor separation in (a) turn on time and (b) on resistance. (a) will mean that there will be a brief transient on one channel before the other turns on and (b) means that the current drawn through the two channels will be unequal.

The differences will usually be small enough to not be a cause for too much worry except if you've also got highly sensitive systems on the same supply lines or physically very close to it. For most practical purposes it's fine, and personally I've generally preferred to use the L293 in parallel instead of the L298 if the current is under an ampere per motor because of the headache L298's package brings to the table.

• I will try to use it in parallel and see how the chip behaves. If it burst into a flame i will extinguish it :) – Gossamer Mar 20 '13 at 13:02

No It is not good to use L293D in this particular case. Better you use L298N, It has a better capacity (upto 2A). It'll be better for your application.

• Unfortunately i have bag of L293D in my drawer :) If it is not possible to achieve what i want with them, then i will order 298N – Gossamer Mar 20 '13 at 9:32

You're never on the safe side operating so close to the maximum rating of an IC like that.

IPC-9592A says that a bipolar linear IC (which most likely describes this driver), at a minimum (Class I stress factor) should be derated to 90% of its maximum output current and have a maximum junction temperature of 115°C.

With a DIP IC, the amount of copper connected to the pins of the device will influence the junction temperature, as conduction from the die through the bonding wires to the legs is the 'best' (albeit not so great) way for heat to escape. Read: if your layout is flimsy, the junction will be hotter than predicted.

Since you have many IC's, I would consider using one IC per motor, paralleling at least two drivers per motor (as described by other answers) - that way the average per-driver current will be below the absolute maximum, and the total power needed divided up over multiple junctions. (Also, if one driver blows, it doesn't take down all the motors.)