DRV8701_15 Datasheet, PDF (32/42 Pages) Texas Instruments – DRV8701 Brushed DC Motor Full-Bridge Gate Driver

DRV8701
SLVSCX5B – MARCH 2015 – REVISED JULY 2015
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8.2.3.2 VM Boost Voltage
To determine an effective voltage to boost VM, first determine the minimum VBAT at which the system must
operate. Select VM such that the gate driver clamps do not turn on during normal operation.
VBAT + 11.5 V
VM <
2
(10)
Example: If VBAT minimum is 4.0 V,
VM < 7.75 V
So VM = 7 V is selected to allow for adequate margin.
9 Power Supply Recommendations
The DRV8701 is designed to operate from an input voltage supply (VM) range between 5.9 and 45 V. A 0.1-µF
ceramic capacitor rated for VM must be placed as close to the DRV8701 as possible. In addition, the designer
must include a bulk capacitor with a valued of at least 10 µF on VM.
Bypassing the external H-bridge FETs requires additional bulk capacitance.
9.1 Bulk Capacitance Sizing
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 datasheet 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 41. 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.
32
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