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| DRV8821_16 Datasheet, PDF (17/32 Pages) Texas Instruments – Dual Stepper Motor Controller and Driver | |||
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www.ti.com
Typical Application (continued)
8.2.1 Design Requirements
Table 3 shows the design parameters.
DRV8821
SLVS912J â JANUARY 2009 â REVISED JANUARY 2016
Table 3. Design Parameters
DESIGN PARAMETER
Supply voltage
Motor winding resistance
Motor step full angle
Target microstepping angle
Target motor speed
Target full-scale current
REFERENCE
VM
RL
θstep
nm
V
IFS
EXAMPLE VALUE
24 V
7.4 â¦/phase
1.8°/step
1/8 step
120 rpm
1A
8.2.2 Detailed Design Procedure
8.2.2.1 Stepper Motor Speed
The first step in configuring the DRV8821 requires the desired motor speed and stepping level. The DRV8821
can support from full step to 1/8 step mode. If the target motor speed is too high, the motor will not spin. Make
sure that the motor can support the target speed. For a desired motor speed (v), a microstepping level (nm), and
motor full step angle (θstep).
Æstep
(steps
/
s)
=
qstep
(°
/
step)
v (rpm) ´ 360 (° / rot)
´ nm (steps / mirostep)
´
60
(s
/
min)
(2)
θstep can be found in the stepper motor data sheet or often written on the motor itself.
For DRV8821, the microstepping levels are set by the xUSM0/xUSM1 pins and can be any of the settings in
Table 1. Higher microstepping means a smoother motor motion and less audible noise, but increases the
switching losses and requires a higher Æstep to achieve the same motor speed.
8.2.2.2 Current Regulation
The chopping current (ICHOP) is the maximum current driven through either winding. This quality will depend on
the sense resistor value (RXISEN).
ICHOP
=
VREFX
5 ´ RISENSE
(3)
ICHOP is set by a comparator which compares the voltage across RXISEN to a reference voltage. Note that ICHOP
must follow Equation 4 to avoid saturating the motor.
ICHOP
(A
)
<
RL
(W)
+
2
´
VM (V)
RDS(ON) (W)+
RSENSE (W)
where
⢠VM is the motor supply voltage.
⢠RL is the motor winding resistance.
(4)
Copyright © 2009â2016, Texas Instruments Incorporated
Product Folder Links: DRV8821
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