Datasheet

TMC2041 DATASHEET (Rev. 1.02 / 2017-MAY-16) 33
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Parameter
Description
Setting
Comment
IRUN
Current scale when motor is running. Scales coil
current values as taken from the internal sine
wave table. For high precision motor operation,
work with a current scaling factor in the range 16
to 31, because scaling down the current values
reduces the effective microstep resolution by
making microsteps coarser. This setting also
controls the maximum current value set by
coolStep.
0 … 31
scaling factor
1/32, 2/32, … 32/32
IHOLD
Identical to IRUN, but for motor in stand still.
IHOLD
DELAY
Allows smooth current reduction from run current
to hold current. IHOLDDELAY controls the number
of clock cycles for motor power down after
TZEROWAIT in increments of 2^18 clocks: 0=instant
power down, 1..15: Current reduction delay per
current step in multiple of 2^18 clocks.
Example: When using IRUN=31 and IHOLD=16, 15
current steps are required for hold current
reduction. A IHOLDDELAY setting of 4 thus results
in a power down time of 4*15*2^18 clock cycles,
i.e. roughly one second at 16MHz.
0
instant IHOLD
1 …15
1*2
18
… 15*2
18
clocks per current
decrement
vsense
Allows control of the sense resistor voltage range
for full scale current.
0
V
FS
= 0.32 V
1
V
FS
= 0.18 V
7.1 Sense Resistors
Sense resistors should be carefully selected. The full motor current flows through the sense resistors.
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 on the sense voltage inputs
leading to unstable measurement results. 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.
The peak sense resistor power dissipation is:


 


 

For high current applications, power dissipation is halved by using the low vsense setting and using
an adapted resistance value. Please be aware, that in this case any voltage drop in PCB traces has a
larger influence on the result. A compact layout with massive ground plane is best to avoid parasitic
resistance effects.