Choosing bootstrap capacitor for MOSFET driver
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.