TMC262 DATASHEET (Rev. 2.07 / 2013-FEB-14)
31
8 Current Setting
The internal 5V supply voltage available at the pin 5VOUT is used as a reference for the coil current
regulation based on the sense resistor voltage measurement. The desired maximum motor current is
set by selecting an appropriate value for the sense resistor. The sense resistor voltage range can be
selected by the VSENSE bit in the DRVCONF register. The low sensitivity (high sense resistor voltage,
VSENSE=0) brings best and most robust current regulation, while high sensitivity (low sense resistor
voltage, VSENSE=1) reduces power dissipation in the sense resistor. This setting reduces the power
dissipation in the sense resistor by nearly half.
After choosing the VSENSE setting and selecting the sense resistor, the currents to both coils are
scaled by the 5-bit current scale parameter CS in the SGCSCONF register. The sense resistor value is
chosen so that the maximum desired current (or slightly more) flows at the maximum current setting
(CS = %11111).
Using the internal sine wave table, which has amplitude of 248, the RMS motor current can be
calculated by:
ꢮꢒ ꢯ ꢐ
ꢰꢦ
ꢲꢳꢭ
ꢐ
ꢪꢫꢬꢭ
ꢌ
ꢱ
ꢱ
ꢴꢭꢵꢶꢭꢵ
ꢦ
√
The momentary motor current is calculated as:
ꢮꢹꢴꢴꢺꢻꢓ
ꢼꢽꢾ ꢱ
ꢮꢒ ꢯ ꢐ
ꢰꢦ
ꢲ
ꢳꢭ
ꢪꢬꢷꢸ
ꢌ
ꢱ
ꢦꢧꢿ
ꢴꢭꢵꢶꢭꢵ
where:
CS is the effective current scale setting as set by the CS bits and modified by coolStep. The effective
value ranges from 0 to 31.
VFS is the sense resistor voltage at full scale, as selected by the VSENSE control bit (refer to the
electrical characteristics).
CURRENTA/B is the value set by the current setting in SPI mode or the internal sine table in STEP/DIR
mode.
Parameter
Description
Setting
Comment
CS
Current scale. Scales both coil current values as 0 … 31
taken from the internal sine wave table or from
the SPI interface. 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™.
Scaling factor:
1/32, 2/32, … 32/32
VSENSE
Allows control of the sense resistor voltage 0
310mV
165mV
range or adaptation of one electronic module to
1
different maximum motor currents.
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
