TMC2160 DATASHEET (Rev. 1.02 / 2018-NOV-19)
61
8 Selecting Sense Resistors
The TMC2160 provides several means to set the motor current: Sense resistors, GLOBALSCALER and
currentscale CS. To adapt a drive to the motor, choose a sense-resistor value fitting or slightly
exceeding the maximum desired current at 100% settings of the scalers. Fine-tune the current to the
specific motor via the 8 bit GLOBALSCALER. Situation specific motor current adaptation is done by 5
bit scalers (actual scale can be read via CS), controlled by coolStep, run- and hold current (IRUN,
IHOLD). This makes the CS control compatible to other TRINAMIC ICs.
Set the desired maximum motor current by selecting an appropriate value for the sense resistor. The
following table shows the RMS current values which are reached using standard resistors.
CHOICE OF RSENSE AND RESULTING MAX. MOTOR CURRENT
WITH GLOBALSCALER=255
RSENSE [Ω]
RMS current [A]
(CS=31)
Sine wave peak
current [A] (CS=31)
0.22
0.15
0.12
0.10
0.075
0.066
0.050
0.033
0.022
1.1
1.6
2.0
2.3
3.1
3.5
4.7
7.1
1.5
2.2
2.8
3.3
4.4
5.0
6.6
10.0
15.0
10.6
Sense resistors should be carefully selected. The full motor current flows through the sense resistors.
Due to chopper operation the sense resistors see pulsed current from the MOSFET bridges. Therefore,
a low-inductance type such as film or composition resistors is required to prevent voltage spikes
causing ringing on the sense voltage inputs leading to unstable measurement results. Also, a low-
inductance, low-resistance PCB layout is essential. A massive ground plane is best. Please also refer to
layout considerations in chapter 25.
The sense resistor sets the upper current which can be set by software settings IRUN, IHOLD and
GLOBALSCALER. Choose the sense resistor value so that the maximum desired current (or slightly
more) flows at the maximum current setting (GLOBALSCALER = 0 and IRUN = 31).
CALCULATION OF RMS CURRENT
퐺ꢎꢌꢜꢉꢎ푆ꢍꢉꢎ퐸푅 ꢍ푆 + 1
푉
1
ꢑꢏ
퐼ꢛ푀ꢏ
=
∗
∗
∗
256
32
푅ꢏꢐ푁ꢏꢐ
2
√
The momentary motor current is calculated by:
ꢍ푈푅퐴/퐵
248
퐺ꢎꢌꢜꢉꢎ푆ꢍꢉꢎ퐸푅
ꢍ푆 + 1
32
푉
ꢑꢏ
퐼푀푂푇
=
∗
∗
∗
256
푅ꢏꢐ푁ꢏꢐ
GLOBALSCALER is the global current scaler. A setting of 0 is treated as full scale (256).
CS is the current scale setting as set by the IHOLD and IRUN and coolStep.
VFS is the full scale voltage (please refer to electrical characteristics, VSRT).
CURA/B is the actual value from the internal sine wave table.
248 is the amplitude of the internal sine wave table.
The sense resistor needs to be able to conduct the peak motor coil current in motor standstill
conditions, unless standby power is reduced. Under normal conditions, the sense resistor conducts
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