Datasheet

TMC2590 DATASHEET (V1.0 / 2019-FEB-22) 36
www.trinamic.com
9.1 Sense Resistors
Sense resistors should be carefully selected. The full motor current flows through the sense resistors.
As they also see the switching spikes from the MOSFET bridges, a low-inductance type such as film or
composition resistors is required to prevent spikes causing ringing. A low-inductance, low-resistance
PCB layout is essential. Keep the high-current interconnections as short as possible as shown in
Figure 9.1. A massive ground plane is best. Because the sense resistor inputs are susceptible to
damage from negative overvoltages, an additional input protection resistor helps protect against a
motor cable break or load effects from long motor cables.
SRA
SRB
10R to 47R
10R to 47R
optional input
protection resistors
MOSFET
bridge
MOSFET
bridge
GND
TMC2590
Power
supply GND
Thick and straight
interconnections – use a
solid GND plane in the
PCB
SRAL
SRBL
Connect near sense
resistor GND terminal
R
SENSE
R
SENSE
Connect near upper
sense resistor terminal
Figure 9.1 Sense resistor grounding and protection components
The sense resistor needs to be able to conduct the peak motor coil current, especially in motor
standstill conditions, unless standby power is reduced. Under normal conditions, the sense resistor
sees the motor coil current with a duty cycle well below 50%.
The peak sense resistor power dissipation is:
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For high-current applications, power dissipation is halved by using the lower sense resistor voltage
setting and the corresponding lower resistance value. In this case, any voltage drop in the PCB traces
has a larger influence on the result. A compact power stage layout with massive ground plane is best
to avoid parasitic resistance effects.
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. The
resulting application current will be slightly lower due to slow decay phase and trace resistance.
CHOICE OF R
SENSE
AND RESULTING MAX. MOTOR CURRENT FOR CS=31
R
SENSE
[Ω]
RMS current [A] VSENSE=0
RMS current [A] VSENSE=1
0.33
0.7
0.35
0.27
0.85
0.45
0.22
1.05
0.55
0.15
1.5
0.8
0.12
1.9
1.0
0.10
2.3
1.2
0.075
3.1
1.6
0.066
3.5
1.9
0.050
4.6
2.5