DRV8870_16 Datasheet, PDF (14/25 Pages) Texas Instruments – Brushed DC Motor Driver

DRV8870
SLVSCY8A – AUGUST 2015 – REVISED JANUARY 2016
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’s 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 will limit the rate current can change from the
power supply. If the local bulk capacitance is too small, the system will respond 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 sized bulk capacitor.
Power Supply
Parasitic Wire
Inductance
Motor Drive System
VBB
+
+
Motor
±
Driver
GND
Local
Bulk Capacitor
IC Bypass
Capacitor
Figure 14. 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.
14
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