Datasheet
TMC4361A Datasheet | Document Revision 1.22 • 2017-JAN-12
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Read entire documentation; especially the “Supplemental Directives” on page 224.
MAIN MANUAL
Back-EMF Compensation during Closed-loop Operation
When higher velocities are reached, a phase shift between current and voltage occurs at the
motor coils. Consequently, current control is transformed into voltage control.
This motor- and setup-dependent effect must be compensated because currents are still
continuously assigned for motor control. TMC4361A attributes γ-correction to the
compensation process, which adds a velocity-dependent angle - in motion direction - to the
current commutation angle.
Gamma correction constantly adds one compensation angle, GAMMA, to the actual
commutation angle; because the velocity-dependent amount of the influence of Back-
EMF, GAMMA is also velocity-dependent. Thus, velocity limits are assigned. These
limits are based on REAL motor velocity
V_ENC
(register 0x65). The value of the motor
velocity is internally calculated and can be filtered (
V_ENC_MEAN
register 0x66) to
smoothen the γ-correction, which is explained in the next section.
In order to configure and enable Back-EMF compensation during closed-
loop operation, do as follows:
Action:
Set proper
CL_GAMMA
register 0x1C.
Set proper
CL_VMIN_EMF
register 0x60.
Set proper
CL_VMAX_EMF
register 0x61.
Set
cl_emf_en
= 1 (
ENC_IN_CONF
register 0x07).
Result:
Back-EMF compensation during closed-loop operation is enabled.
CL_GAMMA
represents the maximum value of GAMMA. Per default,
CL_GAMMA
is set to its
maximal possible value of 255, which represents a 90° angle.
The following compensation situations are possible:
1. In case |
V_ENC_MEAN
| ≤
CL_VMIN_EMF
, GAMMA is set to 0.
2. In case |
V_ENC_MEAN
| >
CL_VMIN_EMF
and
|
V_ENC_MEAN
| ≤ (
CL_VMIN_EMF + CL_VADD_EMF
)
,
GAMMA is scaled linearly
between 0 and its maximum value.
3. In case |
V_ENC_MEAN
| > (
CL_VMIN_EMF + CL_VADD_EMF
),
GAMMA =
CL_GAMMA
.
The chart below identifies the actual parameter GAMMA, which is dependent on the
above described situations:
If γ-correction is turned on, the maximum possible commutation is
(
CL_BETA
+
CL_GAMMA
).
This value must not exceed 180° (511 microsteps at 256 microsteps per fullstep)
because angles of 180° or more will result in unwanted motion direction changes.
Load Angle
Calculation
Areas of
Special
Concern
!
Figure 69: Calculation of the actual Load Angle GAMMA
GAMMA
Usually 255 (=90°)
V_ENC_MEAN
CL_VMIN_EMF
CL_VADD_EMF
CL_GAMMA