I'm designing an H-bridge motor controller with synchronous rectification similar to the Ti Stellaris RDK-BDC24 link here. Synchronous rectification has the promise of handling the back-emf from a motor more efficiently than schottky diodes, but requires a control signal at the transistor gates. If my motor is on and I have a black out, there will be no control signals sent to the H bridge to protect the circuit from the back-emf and poof! I've got some magic smoke.
How should I design my motor controller to have enough power to stay alive long enough for the back-emf spike? The ti motor controller has, what looks like, a 1800uF cap to keep the microprocessor alive. I'm shooting for my circuit to tolerate 30A continuous to a 12V motor.