TO-220 case violates DRU?

Community PCB Design
1

Hi Everyone,

I am still very new to all of this. I’m trying to include the LM2575 switching regulator (TO-220 case) on my board. I found a part in the ads4 library called LM2991 which has the TO-220 case, so I copied it over to my library and created the LM2575 symbol and device. The problem is that when I add it, the pads in the board layout are automatically expanded such that they overlap. I determined that this is because the SparkFun DRU file has a 12mil min for pads in the ‘restring’ tab. It also has a ‘25% of drill hole’ rule. Since the TO-200 violates both of these, the pads are automatically being expanded. However, they then violate the clearance/overlap rule.

How would you recommend proceeding? It seems really risky to change the DRU 12mil min AND the 25% min to smaller values because there are other components on my board with pads which are currently being expanded by these rules (these just don’t violate the clearance rule and are therefore have not been a problem). I would hate to shrink all of those pads just to make the TO-220 work. I can’t redesign the TO-220 because if I make the pads large enough to not violate the DRU minimums, they will then violate the DRU overlap rules. Should I just not be using the TO-220?

Thanks!

Josh

2

What is the problem? TO-220 pins are on 0.100 (100 mil) spacing. You could have a 60 mil wide pad with a 40 mil hole, and still have 40 mils spacing between pads. Or you could use 70 mil wide pads and 30 mil spacing.

I would not use round pads. I would use elongated pads of some sort.

Also consider whether to stand the part up, or to lay it over. If lying down, you could stagger the pins for even more spacing. Check your heat sinking. Adding lots of copper connected to the big tab can be useful for getting rid of heat.

3

Actually, the LM2575 has 5 pins. Which means they are .067 inches apart. I see that there is also a 3 pin version of the TO-220, is this what you are referring to?

4

Yes. I was unaware of a 5-pin TO-220.

5

I thought a 5 pin to-220 was called a to-220-5 or something?

6

Ah - the TO220 - another of lifes mysteries.

Like the device can work at voltages measured in several hundred volts (I.E. 800+) yet the pins are only .1" apart ctr<>ctr which

violates voltage spacing rules.

They are fun :smiley: