User Manual

TMCM-1180 and PD86-1180 Hardware Manual (V1.05 / 2013-JUL-26) 22
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7.1.4 Stepper Motor Driver
The TMC262A-PC is an energy efficient high current high precision microstepping driver IC for bipolar stepper
motors. This driver on the TMCM-1180 module is a special version of the TMC262 power driver for PANdrives
with QSH8618 motors.
Its unique high resolution sensorless load detection stallGuard2 is used for a special integrated load
dependent current control feature called coolStep. The ability to read out the load and detect an overload
makes the TMC262 an optimum choice for drives where a high reliability is desired. The TMC262 can be
driven with step/direction signals as well as by serial SPI™.
stallGuard2 reading
0=maximum load
motor current increment area
motor current reduction area
stall possible
SEMIN
SEMAX+SEMIN+1
Zeit
motor current
current setting CS
(upper limit)
½ or ¼ CS
(lower limit)
mechanical load
current increment due to
increased load
slow current reduction due
to reduced motor load
load angle optimized load angle optimized
load
angle
optimized
Figure 7.2 Motor current control via coolStep adapts motor current to motor load
The coolStep current regulator allows to control the reaction of the driver to increasing
or decreasing load. The internal regulator uses two thresholds to determine the
minimum and the maximum load angle for optimum motor operation. The current
increment speed and the current decrement speed can be adapted to the application.
Additionally, the lower current limit can be set in relation to the upper current limit set
by the current scale parameter CS.
7.1.5 sensOstep Encoder
The sensOstep encoder used in this unit is based on a magnetic angular position encoder system with low
resolution. It consists of a small magnet positioned at the back end of a stepper motor axis and a Hall-
sensor IC with integrated digital signal processing (e.g. for automatic gain control, temperature
compensation etc.) placed above the magnet on the back side of a motor mounted printed circuit board.
The encoder offers a resolutions of 8 bit (256 steps) per revolution which is completely sufficient for
detecting step losses with a standard 1.8° stepper motors.