DRV8850_16 Datasheet, PDF (21/30 Pages) Texas Instruments – Low-Voltage H-Bridge IC with LDO Voltage Regulator

www.ti.com
9 Power Supply Recommendations
DRV8850
SLVSCC0B – NOVEMBER 2013 – REVISED DECEMBER 2015
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
VM
+
+
Motor
–
Driver
GND
Local
Bulk Capacitor
IC Bypass
Capacitor
Figure 21. 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.
10 Layout
10.1 Layout Guidelines
• The bulk capacitor should be placed to minimize the distance of the high-current path through the motor
driver device. The connecting metal trace widths should be as wide as possible, and numerous vias should
be used when connecting PCB layers. These practices minimize inductance and allow the bulk capacitor to
deliver high current.
• Small-value capacitors should be ceramic, and placed close to the device pins.
• The high-current device outputs should use wide metal traces.
• The device thermal pad should be soldered to the PCB top-layer ground plane. Multiple vias should be used
to connect to a large bottom-layer ground plane. The use of large metal planes and multiple vias help
dissipate the I² × R_DS(on) heat that is generated in the device.
Copyright © 2013–2015, Texas Instruments Incorporated
Product Folder Links: DRV8850
Submit Documentation Feedback
21