TMC2041 DATASHEET (Rev. 1.02 / 2017-MAY-16)
32
7 Current Setting
The internal 5V supply voltage available at the pin 5VOUT is used as a reference for the coil current
regulation based on the sense resistor voltage measurement. The desired maximum motor current is
set by selecting an appropriate value for the sense resistor. The sense resistor voltage range can be
selected by the vsense bit in CHOPCONF. The low sensitivity setting (high sense resistor voltage,
vsense=0) brings best and most robust current regulation, while high sensitivity (low sense resistor
voltage, vsense=1) reduces power dissipation in the sense resistor. The high sensitivity setting reduces
the power dissipation in the sense resistor by nearly half.
After choosing the vsense setting and selecting the sense resistor, the currents to both coils are
scaled by the 5-bit current scale parameters (IHOLD, IRUN). The sense resistor value is chosen so that
the maximum desired current (or slightly more) flows at the maximum current setting (IRUN =
%11111).
Using the internal sine wave table, which has the amplitude of 248, the RMS motor current can be
calculated by:
퐶ꢁ + ꢂ
3ꢃ
푉퐹푆
ꢂ
퐼ꢀ푀푆
=
∗
∗
푅푆퐸푁푆퐸 + ꢃꢄ푚Ω
ꢃ
√
The momentary motor current is calculated by:
퐶푈푅퐴/퐵
퐶ꢁ + ꢂ
푉
퐹푆
퐼푀푂푇
=
∗
∗
ꢃ4ꢅ
3ꢃ
푅푆퐸푁푆퐸 + ꢃꢄ푚Ω
CS is the current scale setting as set by the IHOLD and IRUN and coolStep.
VFS is the full scale voltage as determined by vsense control bit (please refer to electrical
characteristics, VSRTL and VSRTH).
CURA/B is the actual value from the internal sine wave table.
The internal resistance of 20mΩ will be increased by external trace resistance, 5mΩ are realistic.
CHOICE OF RSENSE AND RESULTING MAX. MOTOR CURRENT
RSENSE [Ω]
RMS current [A]
(CS=31, vsense=0)
RMS current [A]
(CS=31, vsense=1)
1.00
0.82
0.75
0.68
0.50
0.47
0.33
0.27
0.22
0.15
0.21
0.26
0.28
0.31
0.42
0.45
0.63
0.76
0.91
1.29*)
0.12
0.15
0.16
0.18
0.24
0.25
0.35
0.43
0.51
0.72
*) Value exceeds upper current rating for single motor operation.
Hint
For best precision of current setting, it is advised to measure and fine tune the current in the
application.
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
