TMC4671 Datasheet • IC Version V1.00 | Document Revision V1.04 • 2018-Dec-11
10 / 157
3.5.1 Coordinate Transformations - Clarke, Park, iClarke, iPark
The FOC requires different coordinate transformations formulated as a set of matrix multiplications. These
are the Clarke Transformation (Clarke), the Park Transformation (Park), the inverse Park Transforma-
tion (iPark) and the inverse Clarke Transformation (iClarke). Some put Park and Clarke together as DQ
transformation and Park and Clarke as inverse DQ transformation.
The TMC4671 takes care of the required transformations so the user no longer has to fight with implemen-
tation details of these transformations.
3.5.2 Measurement of Stator Coil Currents
The measurement of the stator coil currents is required for the FOC to calculate a magnetic axis out of the
stator field caused by the currents flowing through the stator coils.
Coil current stands for motor torque in context of FOC. This is because motor torque is proportional
to motor current, defined by the torque constant of a motor. In addition, the torque depends on the
orientation of the rotor of the motor relative to the magnetic field produced by the current through the
coils of the stator of the motor.
3.5.3 Stator Coil Currents I_U, I_V, I_W and Association to Terminal Voltages U_U, U_V, U_W
The correct association between stator terminal voltages U_U, U_V, U_W and stator coil currents I_U, I_V,
I_W is essential for the FOC. In addition to the association, the signs of each current channel need to
fit. Signs of the current can be adapted numerically by the ADC scaler. The mapping of ADC channels is
programmable via configuration registers for the ADC selector. Initial setup is supported by the integrated
open loop encoder block, that can support the user to turn a motor open loop.
3.5.3.1 Chain of Gains for ADC Raw Values
An ADC raw value is a result of a chain of gains that determine it. A coil current I_SENSE flowing through a
sense resistor causes a voltage difference according to Ohm’s law. The resulting ADC raw value is a result
of the analog signal path according to
ADC_RAW = (I_SENSE ∗ ADC_GAIN) + ADC_OFFSET.
(1)
The ADC_GAIN is a result of a chain of gains with individual signs. The sign of the ADC_GAIN is positive
or negative, depending on the association of connections between sense amplifier inputs and the sense
resistor terminals. The ADC_OFFSET is the result of electrical offsets of the phase current measurement
signal path. For the TMC4671, the maximum ADC_RAW value ADC_RAW_MAX = (216
ADC raw value is ADC_RAW_MIN = 0.
−
1) and the minimum
ADC_GAIN
=
(
I_SENSE_MAX ∗ R_SENSE
SENSE_AMPLIFIER_GAIN
)
(2)
∗
∗
(
ADC_RAW_MAX/ADC_U_MAX
)
For the FOC, the ADC_RAW is scaled by the ADC scaler of the TMC4671 together with subtraction of offset
to compensate it. Internally, the TMC4671 FOC engine calculates with s16 values. Thus, the ADC scaling
needs to be chosen so that the measured currents fit into the s16 range. With the ADC scaler, the user can
choose a scaling with physical units like [mA].
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