I'm planning a half-bridge driver with bootstrap IC-s. My motor runs on 12V, with 50-60A. I linked the schematic. I supply the bootstrap from an other battery (7.2V). Due to the big current, can the ground potential level change? In this schematic the ground of the batteries is connected to each other. I fear that the potential level increase/decrease can damage the other part of the electronics, that is supplied from the 7.2V, too. I found a datasheet: http://www.irf.com/product-info/datasheets/data/ir2184.pdf, where two types is introduced, a coupled (IR2184), and a decoupled bootstrap IC (IR21844). What are the advantages/disadvantages both of them?
The answer to your first question is yes. Now regarding the two ICs:
First, with the IR21844 you can set the dead time. In the simpler IR2184 it's preset.
Second, the 21844 has separate ground pins for the driving logic (VSS) and MOSFET grounds (COM), which is probably what you refer to by 21844 being "decoupled". It is certainly advantageous for your high-current application, as this IR FAQ explains:
with the potential of generating higher -Ldi/dt voltage spikes on COM, later ICs separated Vss and COM to increase the noise immunity between logic and power grounds, so that voltage spikes on COM did not cause the logic ground to dip below zero volts and generate false input signals. In these cases separate Vss and COM pins are provided.
On the downside, the 21844 needs more external parts and probably costs more itself too (bigger package).