Datasheet

TMC4671 Datasheet • IC Version V1.3 | Document Revision V2.00 • 2020-Apr-17
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Figure 35: Biquad Filters
The biquad filter for the position target value is intended to be used as a low-pass filter for smoothening
position input to the control structure. It is evaluated in every PWM cycle, or down-sampled according to
the down-sampling factor for the velocity and position controllers. After powering on it is disabled.
The biquad filter for the flux target value is also intended to be used as a low-pass filter for input values
from the user’s microcontroller. Sampling frequency is fixed to the PWM frequency.
The biquad filter for the torque target value can be used as a low-pass filter for bandwidth limitation
and noise suppression. Moreover, it can be designed to suppress a resonance or anti-resonance. Same
statements are correct for the velocity biquad filter. Both filters’ sampling times are fixed to the PWM
period.
The velocity target value biquad is configured as a second order low-pass with a cutoff frequency at 200 Hz
- by default at a sampling frequency of 25 kHz. Biquad filters can be activated separately.
4.8.2 Standard Velocity Filter
By using the standard velocity measurement algorithm, the default velocity filter is enabled and can not be
switched off. The standard velocity filter is a low-pass filter with a cutoff frequency of 20 Hz (slope of -20
dB/Decade). In this configuration, a new velocity is calculated at a sample rate of approx. 4369.067 Hz.
This configuration is intended to be used in low-performance applications with a simple position feedback
system like digital Hall sensors.
4.8.3 Feed-Forward Control Structure
The TMC4671 provides a feed-forward control structure for torque target value and velocity target value.
The structure is intended to support controllers at high dynamic input profiles. It can be switched on when
using the advanced PI controller structure. The feed-forward value is calculated with a DT1 (36) element.
Each DT1 element can be parametrized with two parameters.
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