Datasheet

TMC4671 Datasheet • IC Version V1.3 | Document Revision V2.00 • 2020-Apr-17

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Figure 36: DT1 Element Structure

Equations:

e = X − int_val (46)

int_val =

a_0 e dt (47)

Y = b_1 · e (48)

The coeﬃcients a_0 and b_1 are represented in Q2.30 format. Registers for parametrization of the

feed-forward control structure are feed_forward_velocity_gain, feed_forward_velocity_ﬁlter_constant,

feed_forward_torque_gain, and feed_forward_torque_ﬁlter_constant.

The input target value to the velocity feed-forward entity is the ﬁltered position target value. For the torque

feed-forward entity the output of the velocity feed-forward entity is used. Sampling time for both entities’

integrators is ﬁxed to the PWM frequency.

The feed-forward control structure can be activated via register MODE_FF. With MODE_FF set to Zero, the

control structure is deactivated, value 1 activates feed-forward control from position target to velocity target

and value 2 activates additionally the torque feed-forward path. Registers FF_VELOCITY and FF_TORQUE

display internally calculated feed-forward values.

Parameter a_0 can be set to 2

to deactivate ﬁltering. Smaller gains will ﬁlter the input value. Normalized

output scaling factor b_1 can be calculated by the following equation:

b_1 = F_Sample · 60 · 2

(49)

while F_Sample being the PWM frequency reduced by the downsampling factor (Register MODE_PID_SMPL).

If a diﬀerent position source is selected for position and velocity control loop this also needs to be taken

into account by number of pole pairs or other relation. Please consider data range being signed integer 32

bits for both parameters.

Note

The feed forward control structure normalization of Q2.30 does not suit the usual

application as feed forward control structure due to missing ampliﬁcation possibil-

ity. Therefore, software feed forward control via oﬀset registers is recommended.

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