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? enter image description here

  • \$\begingroup\$ 50 or 60 amps will probably produce a measurable voltage drop in everyday ground connections, yes. You will have to decide if it is better to have control electronics "ride" that difference by being grounded near the load, or "see" that difference by having their own ground path back to the battery. Also consider the effect of inductance if the load current has a pulsed character. \$\endgroup\$ – Chris Stratton Nov 22 '15 at 20:33

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).

  • \$\begingroup\$ Also note that this [split COM VSS] is not a unique feature of [some] IR chips. Other manufacturers have adopted the same solution for similar ICs, e.g. ti.com/lit/ds/symlink/ucc27714.pdf \$\endgroup\$ – Fizz Nov 23 '15 at 15:22
  • \$\begingroup\$ And for more background material, you'll want to google "ground bounce". A lot of what you'll find on that is about high-speed logic, where the currents aren't all that big but di/dt is. In high-current power applications, the speed may not be that fast, but the large difference in currents is going to have the same net effect. \$\endgroup\$ – Fizz Nov 23 '15 at 15:28

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