Electrical – What should be the voltage rating of bootstrap capacitor

The application note is clear on ceramic vs. electrolytic capacitors:

"Factor 5" (bootstrap capacitor leakage current) "... is only relevant if the bootstrap capacitor is an electrolytic capacitor, and can be ignored if other types of capacitor are used."

The application note also refers to DT98-2a (which itself refers to DT04-04) which despite focusing on IGBTs has this to say:

"To size the bootstrap capacitor, the first step is to establish the minimum voltage drop (\$ \Delta V_{BS}\$) that we have to guarantee when the high side IGBT is on.

If \$V_{GE(min)}\$ is the minimum gate emitter voltage to maintain, the voltage drop must be:

\$ \Delta V_{BS} ≤ V_{CC} −V_F −V_{GE(min)} −V_{CE(on)} \$

under the condition:

\$V_{GE(min)} > (V_{BS(UV)}- \$)

where \$V_{CC}\$ is the IC voltage supply, \$V_F\$ is bootstrap diode forward voltage, \$V_{CE(on)}\$ is emitter-collector voltage of low side IGBT and (\$V_{BS(UV)}-\$) is the high-side supply undervoltage negative going threshold."

With some interpretation, we can see that \$V_{GE(min)} => V_{GS(min)}\$ and \$V_{CE(min)} => V_{DS(min)}\$.

You control the frequency so you should know exactly what it is.

The bootstrap capacitor power cannot be used if you require DC drive from the H-bridge. Each half-bridge must be driven low frequently to 'refresh' the capacitor, or the charge will leak off and the drive to the high-side n-channel MOSFET will be compromised.

If you need to drive it high continuously you must use a different type of power such as a DC-DC converter.