DRV8837_15 Datasheet, PDF (14/24 Pages) Texas Instruments – Low-Voltage H-Bridge Driver

DRV8837, DRV8838
SLVSBA4D – JUNE 2012 – REVISED DECEMBER 2015
9 Power Supply Recommendations
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9.1 Bulk Capacitance
Having appropriate local bulk capacitance is an important factor in motor-drive system design. It is generally
beneficial to have more bulk capacitance, while the disadvantages are increased cost and physical size.
The amount of local capacitance needed depends on a variety of factors, including:
• The highest current required by the motor system
• The power-supply capacitance and ability to source current
• The amount of parasitic inductance between the power supply and motor system
• The acceptable voltage ripple
• The type of motor used (brushed dc, brushless dc, stepper)
• The motor braking method
The inductance between the power supply and motor drive system limits the rate at which 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 value, but system-level testing is required to determine the
appropriate size of bulk capacitor.
Power Supply
Parasitic Wire
Inductance
Motor Drive System
VM
+
+
Motor
–
Driver
GND
Local
Bulk Capacitor
IC Bypass
Capacitor
Figure 15. Example Setup of Motor Drive System With External Power Supply
The voltage rating for bulk capacitors should be higher than the operating voltage, to provide margin for cases
when the motor transfers energy to the supply
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