Hello. I am working on a simple wireless control for a solenoid. I am using an SN75441 to control the solenoid so that I can both extend and retract it. I had the SN75441 wired to an arduino UNO and it worked perfectly. I decided that I wanted to make a single board to be able to perform the same function instead of using a full arduino.
I used Fritzing to design a PCB with both the aTmega328 and the SN75441 on it. I used the recommended 16MHz crystal, 10Kohm resistor, 7805 voltage regulator, and the 10pF and 1uF capacitors. When I use a bench power supply to feed 12v in, the SN75441 chip gets hot enough to burn you and then lets out a fart of smoke. When I replace the chip and change the input to 5v, the chip still gets really hot and does not perform the desired functions the aTmega is telling it to do. Taking the chip off of the board completely allows the serial communication to work perfectly with the computer and the aTmega. I have used a common voltmeter to test for continuity and/or direct shorts and haven't really found anything. There appears to be continuity between the positive and gnd of the battery input but I have checked all of my solder joints and traces and the issue is not with that. I am very confused and do not know where to go from here.
Could the voltage regulator be what is causing the voltmeter to measure continuity between the positive battery input and ground? Any help would be awesome. Thank you.
Hi, have you applied power without the two ICs in circuit, just the caps and regulator, measure the voltage around the various IC pins and check that the appropriate voltages are there.
The regulator could be at fault, the above test will indicate this.
Can you post a picture of the board with the components and IC on board please, both sides thanks.
Make sure ICs are in the correct way. the 75441 should be oriented in the opposite direction to the controller IC.
Hope to help.
Tom.......... 
PS does the IC cook with or without the motor connected?
Did you trace out the pcb ?
Did you breadboard it ?
Do you have pin 8 of the 441 going to Vin?
As usual - not a single decoupling capacitor in the circuit, and Aref shorted to 5V.
Post the schematic and tack on 0.1uF caps from all Vcc pins to Gnd.
Cut the Aref-5V trace, add a 0.1uF cap from Aref to Gnd.
You are not providing much cooling for the '441. Just the little trace between the 4 ground pins.
You don't have the chip plugged in "upside down" do you? It should be oriented with pin 1 at the bottom of the board, opposite that of the '328.
I don't know if you are aware of it but as Crossroads mentioned , the entire section of the 75441 ic layout in the middle of the chip is suppose to be a solid sheet of copper extending out on both side of the chip like a butterfly . All the other traces take a lower priority to cooling. Ideally, it should be a solid strip (not tiny traces like you have) extending out in both directions at least a cm.
I don't think you did a point to point continuity check against a wiring list for that layout .
Thanks for all the replies. It seems I did make the simple mistake originally of having the 441 in upside down. I designed the pcb and knew I needed to put it in facing opposite of the 328 and when I put it in the socket I did not. The board works perfectly now. To answer some of your concerns: The ground pins on the 441 are only like that in the pcb design becuase it was easiest to do it that way while designing in fritzing. I did etch the pcb myself and left all the copper between the four ground pins intact to help with heat as you described. I would like to know what the point of adding all of the .01uF caps would be. Is it necessary to add one on the AREF pin? The way I have it wired up is the way I have seen it on many tutorial sights. Thanks again guys. The board does work but I am of course always looking to make it better so any more advice anyone has would be taken into account. Thanks.
It seems I did make the simple mistake originally of having the 441 in upside down. I designed the pcb and knew I needed to put it in facing opposite of the 328 and when I put it in the socket I did not.
Experience varies directly with equipment ruined.
And
Always blame yourself.
The 0.1uF decoupling caps are needed, see attached.
You should have one on every VCC and AVCC pin of every device.