DRV8874
SLVSF66A –AUGUST 2019–REVISED DECEMBER 2019
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9 Power Supply Recommendations
9.1 Bulk Capacitance
Having appropriate local bulk capacitance is an important factor in motor drive system design. Having more bulk
capacitance is generally beneficial, while the disadvantages are increased cost and physical size.
The amount of local bulk capacitance needed depends on a variety of factors, including:
•
•
•
•
•
The highest current required by the motor or load
The capacitance of the power supply and ability to source current
The amount of parasitic inductance between the power supply and motor system
The acceptable voltage ripple of the system
The motor braking method (if applicable)
The inductance between the power supply and motor drive system limits how the rate current can change from
the power supply. If the local bulk capacitance is too small, the system responds to excessive current demands
or dumps from the motor with a change in voltage. When adequate bulk capacitance is used, the motor voltage
remains stable and high current can be quickly supplied.
The data sheet generally provides a recommended minimum value, but system level testing is required to
determine the appropriately sized bulk capacitor.
Parasitic Wire
Inductance
Motor Drive System
Power Supply
VBB
+
Motor
Driver
+
œ
GND
Local
Bulk Capacitor
IC Bypass
Capacitor
Figure 36. System Supply Parasitics Example
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