I am making some progress to finding the problem. I have found this little tutorial that is very similar to my setting:
**broken link removed**
I tried not connecting a motor and not providing anything to the enable pin. The chip gets hot. I run the regular 5V from the microcontroller and it heats up slowly. I use a 9V and it heats up faster, and with 12V its almost instantly. Could something be wrong with the bridge?
I also noticed that when the higher voltage is not supplied to the chip on pin VCC2 it doesn't heat up. And when I change the Vcc1 with Vcc2 it doesn't heat up. Maybe I have the chip upside down? (this will be ridiculous).
Thanks.