Datasheet

TMC4671 Datasheet • IC Version V1.3 | Document Revision V2.00 • 2020-Apr-17
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3.5.7.1 Direction of Motion - Magnetic Field vs. Position Sensor
For FOC it is essential, that the direction of revolution of the magnetic field is compatible with the direction
of motion of the rotor position reconstructed from encoder signals: For revolution of magnetic field with
positive direction, the decoder position needs to turn into the same positive direction. For revolution of
magnetic field with negative direction, the decoder position needs to turn into the same negative direction.
With an absolute encoder, once adjusted to the relative orientation of the rotor and to the relative
orientation of the stator, one could start the FOC without initialization of the relative orientations.
3.5.7.2 Bang-Bang Initialization of the Encoder
A Bang-Bang initialization is an initialization where the motor is forced with high current into a specific
position. For Bang-Bang initialization, the user sets a current into direction D that is strong enough to
move the rotor into the desired direction. Other initialization methods ramp up the current smoothly and
adjust the current vector to rotor movement detected by the encoder.
3.5.7.3 Encoder Initialization using Hall Sensors
The encoder can be initialized using digital Hall sensor signals. Digital Hall sensor signals give absolute
positions within each electrical period with a resolution of sixty degrees. If the Hall sensor signals are used
to initialize the encoder position on the first change of a Hall sensor signal, an absolute reference within
the electrical period for commutation is given.
3.5.7.4 Minimum Movement Initialization of the Encoder
For minimal movement initialization of the encoder, the user slowly increases a current into direction D
and adjusts an offset of the measured angle in a way that the rotor of the motor does not move during
initialization while the offset of the measured angle is determined.
3.5.8 Knowledge of Relevant Motor Parameters and Position Sensor (Encoder) Parameters
3.5.8.1 Number of Pole Pairs of a Motor
The number of pole pairs is an essential motor parameter. It defines the ratio between electrical revolutions
and mechanical revolutions. For a motor with one pole pair, one mechanical revolution is equivalent to
one electrical revolution. For a motor with npp pole pairs, one mechanical revolution is equivalent to npp
electrical revolutions, with n = 1, 2, 3, 4, . . . .
Some define the number of poles NP instead of number of pole pairs NPP for a motor, which results in a
factor of two that might cause confusion. For the TMC4671, we use NPP number of pole pairs.
3.5.8.2 Number of Encoder Positions per Revolution
For the encoder, the number of positions per revolution (PPR) is an essential parameter. The number of
positions per revolution is essential for the FOC.
Some encoder vendors give the number of lines per revolution (LPR) or just named line count (LC) as
encoder parameter. Line count and positions per revolution might differ by a factor of four. This is because
of the quadrature encoding - A signal and B signal with phase shift - that give four positions per line,
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