TMC428 ETC-unknow, TMC428 Datasheet - Page 17

• Manufacturer Part Number: TMC428
• Description: Intelligent Triple Stepper Motor Controller With Serial Peripheral Interfaces
• Manufacturer: ETC-unknow

TMC428 DATA SHEET (V. 1.00 / February 12, 2001)
is_agtat & is_aleat & is_v0 & a_threshold (IDX=%1000)
These parameters represent current scaling values I
phase: The parameter is_agtat is applied if the acceleration (a) it greater than (gt) a threshold acceleration
(a
acceleration is lower equal (le) than the threshold acceleration. This is the nominal motor current. The
third parameter is_v0 is applied if the stepper motor is at rest, to save power, to keep it cool, and to avoid
noise probably caused by chopper drivers. The parameter a_threshold is the threshold used to compare
with the current acceleration to select the current scale factor. The three parameters is_agtat, is_aleat,
and is_v0 are bit vectors of three bit width. One of these is selected conditionally and assigned to an
interim bit vector i_scale. The current scaling factor I
Table 6 - Current Scale Factors
One of the three scale factors is_agtat, is_aleat, and is_v0 is selected according to Table 7. If the velocity
is zero, the parameter is_v0 is used for scaling. If the velocity is not zero, either is_aleat or is_agtat is
used for scaling, depending on the absolute value of the acceleration and the acceleration threshold
a_threshold.
Table 7 - Current Scale Selection Scheme
The automatic motion dependent current scale feature of the TMC428 is provided primarily for micro step
operational mode. But it may also be applied for full step or half step drivers, if those provide current
control bits. For those drivers, one could initialize the micro step tabular with a constant function, square
function or sine wave using the two most significant DAC bits.
pmul & pdiv (IDX=%1001)
The stepper motors are driven with a trapezoidal velocity profile, which may become triangular if the
maximum velocity is not reached (see Figure 7, 15). Depending on the difference between the target
position x_target and the actual position x_actual, the ramp generator continuously calculates target
velocities v_target for the pulse generator (see Figure 8, page 18). The pulse generator then generates
(micro) step pulses taking into account the motion parameter limits (v_min, v_max, a_max). With a
target velocity proportional to the difference of target position x_target and current position x_actual,
Copyright © 2000, TRINAMIC Microchips GmbH
TRINAMIC
M I C R O C H I P S
t
0
0
0
0
1
1
1
1
v = 0
v ? 0
). This is to increase current during strong acceleration. The parameter is_aleat is applied if the
i_scale
0
0
1
1
0
0
1
1
| a | = a
| a | > a
0
1
0
1
0
1
0
1
threshold
threshold
1 / 8
2 / 8
3 / 8
4 / 8
5 / 8
5 / 8
7 / 8
I
1
s
I
I
I
s
s
s
:=
:=
:=
is_v0
is_aleat
is_agtat
s
s
and are applied to the motor depending on the ramp
is defined in Table 6.
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