[Q1]
Based on the specifications given above, what is the voltage rating of boostrap capacitor CBOOT that should be used?
[Q2]
Simulation based on the specificitions given above was carried out and it worked as expected. However, the constructed synchronous buck converter did not work. The measured output was very low, approaching zero. What are the possible causes to this problem?
[Q2]
What is the best value of VCC in this application?
You are probably not generating a high enough gate-source voltage to turn on the highside MOSFET. The voltage from HO to HS should be high enough to exceed the threshold voltage of the MOSFET. If this device is not turning on, then the output would indeed be very close to zero. Try using Vcc=20V to see if you get a high enough Vgs to turn the highside MOSFET on.
You are probably not generating a high enough gate-source voltage to turn on the highside MOSFET. The voltage from HO to HS should be high enough to exceed the threshold voltage of the MOSFET. If this device is not turning on, then the output would indeed be very close to zero. Try using Vcc=20V to see if you get a high enough Vgs to turn the highside MOSFET on.
Do u think the voltage rating of the boostrap capacitor CBOOT is important for the circuit to operate correctly? If I'm not mistaken, the voltage rating of the CBOOT used in the circuit is 6V or 10V... Pls advise.
I don't think that is a big concern but just to be safe you can choose something with a larger rating. The main point with the rating is that you don't want to overstress the part. So go with something larger for the rating and it should work.