TMC389-EVAL MANUAL (V. 1.10 / 2011-Mar-01)
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Copyright © 2010 TRINAMIC Motion Control GmbH & Co. KG
3.2 Sense resistors and current setting
There is one foot point sense resistor on the board which is realized using two resistors (R15 and
R16). The second resistor can be paralleled using a soldering jumper in order to lower the effective
value and to increase current. As a default, a 150m
Ω 2510 type resistor is used. The second 150mΩ
resistor can be switched in parallel to double the motor current. For different current requirements, the
sense resistors can be exchanged (see table). The sense resistors should be chosen in a way, that
they fit the maximum required motor current. The current can be scaled down in the TMC389, but
scaling down the current too much reduces effective microstep resolution. There also is a half current
setting available (VSENSE=1), which does not affect the microstep resolution. Its main purpose is to
halve the sense resistor power dissipation. At current settings above 5A, take care not to exceed
maximum MOSFET power stage temperature, as the MOSFET power dissipation increases with the
square of the current. On the evaluation board, the distance between MOSFETs and TMC389 is quite
large, so the TMC389 does not directly see MOSFET heating and will not be able to protect the
MOSFETs against overtemperature.
Motor current limit at full current setting via Step/Direction interface (example values):
Sense resistor value
R
SENSE
Current (peak)
I
COIL
Current RMS
I
COILRMS
Current (peak)
I
COIL
Current RMS
I
COILRMS
VSENSE=0, CS=28
VSENSE=1, CS=28
330m
Ω
0.44
0.31
0.81
0.57
330m
Ω || 330mΩ
0.88
0.62
1.62
1.15
220mΩ
0.66
0.47
1.22
0.86
220mΩ || 220mΩ
1.32
0.93
2.43
1.72
150mΩ
0.97
0.68
1.79
1.26
150mΩ || 150mΩ
1.93
1.37
3.57
2.52
100mΩ
1.45
1.02
2.68
1.89
100mΩ || 100mΩ
2.9
2.05
5.36
3.79
75
mΩ || 75mΩ
4.46
3.15
8.24
5.83
In a practical application, especially with low ohmic sense resistors, trace resistance can significantly
influence the reachable current. Care has to be taken to realize a compact layout with low GND
resistance in order to reach a good microstep performance.
Component selection:
It is important to use low inductivity resistors like Vishay WSL2512.
3.3 Power supply filter capacitors
As a chopper operated motor driver draws current in short intervals, it causes noise on the power
supply. Therefore it is important to filter the power supply using a capacitor, in order to reduce
electromagnetic emission (EME) via power supply cables. Further, the capacitor should be able to
store energy fed back from the motor, when the motor becomes decelerated. This depends on the
application velocity and mechanics.
Component selection:
Due to the high frequent ripple, low ESR capacitors are required for this application. The evaluation
board uses Vishay 150RMI series capacitors. These provide a very long life time even at high
environment temperatures. The required total capacity depends on desired motor current and on the
distance to the power supply.
3.4 Optional components
There are optional filter components designed in on the board. These allow experimenting with EME
filters, e.g. RC and LC filter with RC dampening. Please see the board schematic for sample values.
