TMCM-078 Manual (V1.03 / September 10th, 2008)
18
Copyright © 2008, TRINAMIC Motion Control GmbH & Co. KG
5.2.1.2
Operating Mode 1 (PWM)
This mode is identical to the chopper mode 0 (SPI) mode, but it increases the microstep resolution at
low velocities / stand still (up to 64 microsteps are possible).
MOTOR
MAX
,
COIL
N
N
S
N
R
I
V
V
25
...
22
V
V
2
5.2.1.3
Operating Mode 2 (PHASE)
This mode uses a different chopper scheme, which provides a very high microstep resolution and
smooth motor operation. However motor dynamics and maximum velocity are quite limited. Care has
to be taken concerning the selection of motor and supply voltage:
The motor is chopped with 20kHz, and the coil sees a 50% duty cycle at full supply voltage when the
coil current is meant to be zero. This is only true for the average, but the motor still sees an
alternating current and thus an alternating magnetic field. Now, care has to be taken in order to keep
this current to a value which is significantly lower than the motor maximum coil current. If it is too
high, the motor has significant magnetization losses and coil power dissipation, and would get much
too hot, even with zero average current. The only possibility to limit this effect, is to operate with a
comparatively low supply voltage. The following calculation is based on the assumption that full
motor current is set.
Check list:
Please take the motor inductivity L [mH] and motor rated full step coil current I
COIL
[A] from the
motor’s data sheet:
Now choose a supply voltage for the module to fulfil the following comparison:
5
.
0
I
L
s
25
V
COIL
S
mH
L
20
I
V
COIL
S
If your parameters do not fulfil the equation, i.e. you calculate a supply voltage which is below the
modules’ operation specs or which does not fit your system requirements, try the following:
Calculate x:
mH
L
025
.
0
I
V
x
COIL
S
If x is below 0.5, everything is OK.
If x is in the range 0.5 to 1.0, try operating your motor and check if motor or driver gets too hot.
If x is above 1.0, choose one of the other chopper modes.
See also 5.1.1.3 for graphical demonstration.