DRV8426PWPR datasheet(32/49 Pages) TI1

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step

v (rpm)

360 ( / rot)

VWHSV V

( / step) n

(steps / microstep)

60 (s / min)

DRV8426

SLOSE55 – MAY 2020

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Table 13. Design Parameters (continued)

DESIGN PARAMETER

REFERENCE

EXAMPLE VALUE

Target microstepping level

1/8 step

Target motor speed

150 rpm

Target full-scale current

IFS

1 A

8.2.2 Detailed Design Procedure

8.2.2.1 Stepper Motor Speed

The first step in configuring the DRV8426 device 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 speed is too high, the motor does not spin. Make sure that the motor can support

the target speed. Use Equation 1 to calculate ƒstep for a desired motor speed (v), microstepping level (nm), and

motor full step angle (θstep)

(1)

The value of θstep can be found in the stepper motor data sheet, or written on the motor. For example, the motor

in this application is required to rotate at 1.8°/step for a target of 150 rpm at 1/8 microstep mode. Using

Equation 1, ƒstep can be calculated as 4000 Hz.

The microstepping level is set by the M0 and M1 pins and can be any of the settings listed in Table 14. Higher

microstepping results in a smoother motor motion and less audible noise, but requires a higher ƒstep to achieve

the same motor speed.

Table 14. Microstepping Indexer Settings

MODE0

MODE1

STEP MODE

Full step (2-phase excitation) with 100%

current

330k

Ω to

GND

Full step (2-phase excitation) with 71% current

Non-circular 1/2 step

Hi-Z

1/2 step

1/4 step

1/8 step

Hi-Z

1/16 step

Hi-Z

1/32 step

Hi-Z

330k

Ω to

GND

1/64 step

Hi-Z

1/128 step

Hi-Z

1/256 step

8.2.2.2 Current Regulation

In a stepper motor, the full-scale current (IFS) is the maximum current driven through either winding. This quantity

depends on the VREF voltage. The maximum allowable voltage on the VREF pin is 3.3V for DRV8426. DVDD

can be used to provide VREF through a resistor divider. During stepping, IFS defines the current chopping

threshold (ITRIP) for the maximum current step. IFS (A) = VREF (V) / 2.2 (V/A)

8.2.2.3 Decay Modes

The DRV8426 device supports six different decay modes, as shown inTable 8. The current through the motor

windings is regulated using an adjustable fixed-time-off scheme which means that after any drive phase, when a

motor winding current has hit the current chopping threshold (ITRIP), the DRV8426 places the winding in one of

the six decay modes for tOFF. After tOFF, a new drive phase starts.

DRV8426PWPR Datasheet(PDF) 32 Page - Texas Instruments

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