TMC262 DATASHEET (Rev. 2.07 / 2013-FEB-14)
13
5 coolStep Load-Adaptive Current Control
coolStep allows substantial energy savings, especially for motors which see varying loads or operate
at a high duty cycle. Because a stepper motor application needs to work with a torque reserve of 30%
to 50%, even a constant-load application allows significant energy savings because coolStep
automatically enables torque reserve when required. Reducing power consumption keeps the system
cooler, increases motor life, and allows reducing cost in the power supply and cooling components.
Reducing motor current by half results in reducing power by a factor of four.
Energy efficiency
Motor generates less heat -
Less cooling infrastructure -
-
power consumption decreased up to 75%.
improved mechanical precision.
for motor and driver.
Cheaper motor
-
does the job.
0,9
0,8
0,7
0,6
Efficiency with coolStep
Efficiency with 50% torque reserve
0,5
Efficiency
0,4
0,3
0,2
0,1
0
0
50
100
150
200
250
300
350
Velocity [RPM]
Figure 5.1 Energy efficiency example with coolStep
Figure 5.1 shows the efficiency gain of a 42mm stepper motor when using coolStep compared to
standard operation with 50% of torque reserve. coolStep is enabled above 60rpm in the example.
coolStep is controlled by several parameters, but two are critical for understanding how it works:
Parameter
Description
Range
Comment
SEMIN
4-bit unsigned integer that sets a lower 0… 15
threshold. If SG goes below this threshold,
coolStep increases the current to both coils. The
4-bit SEMIN value is scaled by 32 to cover the
lower half of the range of the 10-bit SG value.
(The name of this parameter is derived from
smartEnergy, which is an earlier name for
coolStep.)
lower stallGuard
threshold:
SEMINx32
SEMAX
4-bit unsigned integer that controls an upper 0… 15
threshold. If SG is sampled equal to or above
this threshold enough times, coolStep decreases
the current to both coils. The upper threshold is
(SEMIN + SEMAX + 1) x 32.
upper stallGuard
threshold:
(SEMIN+SEMAX+1)x32
Figure 5.2 shows the operating regions of coolStep. The black line represents the SG measurement
value, the blue line represents the mechanical load applied to the motor, and the red line represents
the current into the motor coils. When the load increases, SG falls below SEMIN, and coolStep
www.trinamic.com
TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
