TMC2100 DATASHEET (Rev. 1.07 / 2017-MAY-15)
23
7 Selecting Sense Resistors
Set the desired maximum motor current by selecting an appropriate value for the sense resistor. The
following table shows the RMS current values which can be reached using standard resistors and
motor types fitting without additional motor current scaling.
CHOICE OF RSENSE AND RESULTING MAX. MOTOR CURRENT
RSENSE [Ω]
RMS current [A]
Fitting motor type
AIN=2.5V (or open),
(examples)
1.00
0.82
0.75
0.68
0.23
0.27
0.30
0.33
0.44
0.47
0.56
0.66
0.79
0.96
1.15
1.35
1.64*)
1.92*)
300mA motor
400mA motor
0.50
470m
390m
330m
270m
220m
180m
150m
120m
100m
500mA motor
600mA motor
700mA motor
800mA motor
1A motor
1.2A motor
1.5A motor
*) Value exceeds upper current rating, scaling down required, e.g. by reduced AIN.
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. Any common GND path for the two sense resistors
must be avoided, because this would lead to coupling between the two current sense signals. A
massive ground plane is best. Please also refer to layout considerations in chapter 16.
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
less than the coil RMS current, because no current flows through the sense resistor during the slow
decay phases. A 0.5W type is sufficient for most applications up to 1.2A RMS current.
The peak sense resistor power dissipation is:
ꢈ
ꢆꢇ푆푀퐴푋 = 퐼퐶푂ꢁ퐿 ∗ 푅푆퐸푁푆퐸
Attention
Be sure to use a symmetrical sense resistor layout and short and straight sense resistor traces of
identical length. Well matching sense resistors ensure best performance.
A compact layout with massive ground plane is best to avoid parasitic resistance effects.
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
