TMC5031 DATASHEET (Rev. 1.11 / 2016-APR-28)
52
10.1.1 Variable Velocity Operation
The SGT setting chosen as a result of the previously described SGT tuning can be used for a certain
velocity range. Outside this range, a stall may not be detected safely, and coolStep might not give the
optimum result.
good operation
range with single
1000
900
800
700
600
500
400
300
200
100
0
20
18
16
14
12
10
8
SGT setting
stallGuard2
reading at
no load
optimum
SGT setting
6
4
2
0
50
100
150
200
250
300
350
400
450
500
550
600
Motor RPM
(200 FS motor)
lower limit for stall
detection
back EMF reaches
supply voltage
Figure 10.2 Example: Optimum SGT setting and stallGuard2 reading with an example motor
In many applications, operation at or near a single operation point is used most of the time and a
single setting is sufficient. The ramp generator provides a lower and an upper velocity threshold to
match this. The stall detection should be ignored and disabled by software outside the determined
operation point, e.g. during acceleration phases preceding a sensorless homing procedure.
In some applications, a velocity dependent tuning of the SGT value can be expedient, using a small
number of support points and linear interpolation.
10.1.2 Small Motors with High Torque Ripple and Resonance
Motors with a high detent torque show an increased variation of the stallGuard2 measurement value
SG with varying motor currents, especially at low currents. For these motors, the current dependency
should be checked for best result.
10.1.3 Temperature Dependence of Motor Coil Resistance
Motors working over a wide temperature range may require temperature correction, because motor
coil resistance increases with rising temperature. This can be corrected as a linear reduction of SG at
increasing temperature, as motor efficiency is reduced.
10.1.4 Accuracy and Reproducibility of stallGuard2 Measurement
In a production environment, it may be desirable to use a fixed SGT value within an application for
one motor type. Most of the unit-to-unit variation in stallGuard2 measurements results from manu-
facturing tolerances in motor construction. The measurement error of stallGuard2 – provided that all
other parameters remain stable – can be as low as:
|
|
푠푡푎푙푙퐺푢푎푟푑 푚푒푎푠푢푟푒푚푒푛푡 푒푟푟표푟 = ±푚푎푥ꢍ1, 푆퐺푇 ꢎ
www.trinamic.com
TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
