SLVSAX9E September 2011 – January 2016 DRV8818
PRODUCTION DATA.
- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Detailed Description
- 8 Application and Implementation
- 9 Power Supply Recommendations
- 10Layout
- 11Device and Documentation Support
- 12Mechanical, Packaging, and Orderable Information
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
8.1 Application Information
The DRV8818 is used for bipolar stepper motor control. The microstepping motor driver provides precise regulation of the coil current and ensures a smooth rotation from the stepper motor.
8.2 Typical Application
Figure 9 shows a common system application of the DRV8818.
Figure 9. Typical Application Schematic
8.2.1 Design Requirements
See Table 3 for the design parameters.
Table 3. Design Parameters
| DESIGN PARAMETER | REFERENCE | EXAMPLE VALUE |
|---|---|---|
| Supply Voltage | VM | 24 V |
| Motor Winding Resistance | RL | 4.0 Ω |
| Motor Winding Inductance | IL | 3.7 mH |
| Motor Full Step Angle | θstep | 1.8°/step |
| Target Microstepping Level | nm | 8 µsteps per step |
| Target Motor Speed | v | 120 rpm |
| Target Full-Scale Current | IFS | 1.25 A |
8.2.2 Detailed Design Procedure
8.2.2.1 Stepper Motor Speed
The first step in configuring the DRV8818 requires the desired motor speed and microstepping level. If the target application requires a constant speed, then a square wave with frequency ƒstep must be applied to the STEP pin.
If the target motor startup speed is too high, the motor will not spin. Make sure that the motor can support the target speed or implement an acceleration profile to bring the motor up to speed.
For a desired motor speed (v), microstepping level (nm), and motor full step angle (θstep),
θstep can be found in the stepper motor data sheet or written on the motor itself.
For the DRV8818, the microstepping level is set by the USMx pins. Higher microstepping will mean a smother motor motion and less audible noise, but will increase switching losses and require a higher fstep to achieve the same motor speed.
8.2.2.2 Current Regulation
In a stepper motor, the set full-scale current (IFS) is the maximum current driven through either winding. This quantity will depend on the VREF analog voltage and the sense resistor value (RSENSE). During stepping, IFS defines the current chopping threshold (ITRIP) for the maximum current step. The gain of DRV8818 is set for 8 V/V.
To achieve IFS = 1.25 A with RSENSE of 0.1 Ω, VREF should be 1.56 V.
8.2.3 Application Curves
Figure 10. Mixed Decay
Figure 12. Mixed Decay on Decreasing Steps
Figure 11. Slow Decay on Increasing Steps