DRV8880_15 Datasheet, PDF (33/48 Pages) Texas Instruments – DRV8880 2-A Stepper Motor Driver With AutoTune™

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DRV8880
SLVSD18A – JUNE 2015 – REVISED JULY 2015
Table 11. Design Parameters (continued)
DESIGN PARAMETER
Target full-scale current
REFERENCE
I_FS
EXAMPLE VALUE
1.5 A
8.2.2 Detailed Design Procedure
8.2.2.1 Stepper Motor Speed
The first step in configuring the DRV8880 requires the desired motor speed and microstepping level. If the target
application requires a constant speed, then a square wave with frequency ƒ_step must be applied to the STEP pin.
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), microstepping level (n_m), and motor full step angle (θ_step),
¦_step
VWHSV 
V

6_step (G
/
step)
v (rpm) K 360 (G / rot)
K n_m (steps / microstep)
K
60
(s
/
min)
(2)
θ_step can be found in the stepper motor data sheet or written on the motor itself.
For the DRV8880, the microstepping level is set by the Mx pins and can be any of the settings in the table below.
Higher microstepping will mean a smother motor motion and less audible noise, but will increase switching
losses and require a higher ƒ_step to achieve the same motor speed.
Table 12. Microstepping Indexer Settings
M1
M0
STEP MODE
0
0
Full step (2-phase excitation) with 71%
current
0
1
Non-circular 1/2 step
1
0
1/2 step
1
1
1/4 step
0
Z
1/8 step
1
Z
1/16 step
Example: Target 120 rpm at 1/8 microstep mode. The motor is 1.8°/step
¦_step
VWHSV

V

1.8G
/
step
120 rpm K
K1/ 8 steps /
360G / rot
microstep
K
60
s
/
min


N+]
(3)
8.2.2.2 Current Regulation
In a stepper motor, the full-scale current (I_FS) is the maximum current driven through either winding. This quantity
will depend on the TRQ pins, the VREF analog voltage, and the sense resistor value (R_SENSE). During stepping,
I_FS defines the current chopping threshold (I_TRIP) for the maximum current step.
I_FS (A)
VREF (V) u TRQ (%)
A_v u R_SENSE (:)
VREF (V) u TRQ (%)
6.6 u R_SENSE (:)
(4)
TRQ is a DAC used to scale the output current. The current scalar value for different inputs is shown below.
Table 13. Torque DAC Settings
TRQ1
1
1
0
0
TRQ0
1
0
1
0
CURRENT SCALAR (TRQ)
25%
50%
75%
100%
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