SITUATION: An integrated circuit, such as the H-bridge or the MAX7219 / MAX7221 LCD driver, gets warm, maybe even too warm to touch.
CAUSE: Most commonly this is the result of reversing the power connections to the integrated circuit. Where +5v or +3.3v should be connected the connection is to GND. Similarly, where GND should be connected the connection goes to a positive voltage.
CORRECTION: Remove power immediately. Verify the power connections are reversed by tracing the wiring. Fix errors.
NOTE: Some integrated circuits are more forgiving than others. The MAX7219/7221 often is undamaged by this reversal, for example. Some integrated circuits will become warm, but not hot, in normal operation. The 7806 voltage regulator, for example, can become warm to the touch but should never be hot enough to cause discomfort. The L293 H-bridge integrated circuit can be fitted with a heat sink, a finned device that radiates generated heat. The lessons on this website do not place a load on this circuit high enough to require this heat sink, however.