TMC2208-LA Datasheet, PDF (51/79 Pages) TRINAMIC Motion Control GmbH & Co. KG. – POWER DRIVER FOR STEPPER MOTORS

TMC220X, TMC222X DATASHEET (Rev. 1.01 / 2016-Nov-16)
51
8 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 R_SENSE AND RESULTING MAX. MOTOR CURRENT
R_SENSE [Ω]
RMS current [A]
Fitting motor type
VREF=2.5V (or open), (examples)
IRUN=31,
vsense=0 (standard)
1.00
0.23
0.82
0.27
0.75
0.30
300mA motor
0.68
0.33
400mA motor
0.50
0.44
470m
0.47
500mA motor
390m
0.56
600mA motor
330m
0.66
700mA motor
270m
0.79
800mA motor
220m
0.96
1A motor
180m
1.15
1.2A motor
150m
1.35
120m
1.64*)
100m
1.92*)
1.5A motor
*) Value exceeds upper current rating, scaling down required, e.g. by reduced VREF.
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 19.
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.
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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