5962-9096201MXA Datasheet, PDF (12/16 Pages) Analog Devices – Variable Resolution, Monolithic esolver-to-Digital Converter

AD2S80A
12
9
6
3
0
–3
–6
–9
–12
0.02f_BW 0.04fBW 0.1f_BW 0.2f_BW 0.4f_BW
f_BW
FREQUENCY
Figure 4. AD2S80A Gain Plot
2f_BW
180
135
90
45
0
–45
–90
–135
–180
0.02f_BW 0.04f_BW 0.1f_BW 0.2f_BW 0.4f_BW
f_BW
FREQUENCY
Figure 5. AD2S80A Phase Plot
2f_BW
OUTPUT
POSITION
t₂
TIME
t₁
Figure 6. AD2S80A Small Step Response
The small signal step response is shown in Figure 6. The time
from the step to the first peak is t₁ and the t₂ is the time from
the step until the converter is settled to 1 LSB. The times t₁ and
t₂ are given approximately by
1
t₁ = _{f BW}
5R
t₂ =
f _BW
×
12
where R = resolution, i.e., 10, 12, 14, or 16.
The large signal step response (for steps greater than 5 degrees)
applies when the error voltage exceeds the linear range of the
converter.
Typically the converter will take 3 times longer to reach the first
peak for a 179 degrees step.
In response to a velocity step, the velocity output will exhibit the
same time response characteristics as outlined above for the
position output.
ACCELERATION ERROR
A tracking converter employing a Type 2 servo loop does not
suffer any velocity lag, however, there is an additional error due
to acceleration. This additional error can be defined using the
acceleration constant K_A of the converter.
Input Acceleration
K _A = _{Error in Output Angle}
The numerator and denominator must have consistent angular
units. For example if K_A is in sec^–2, then the input acceleration
may be specified in degrees/sec² and the error output in degrees.
Angular measurement may also be specified using radians, min-
utes of arc, LSBs, etc.
K_A does not define maximum input acceleration, only the error due
to it’s acceleration. The maximum acceleration allowable before
the converter loses track is dependent on the angular accuracy
requirements of the system.
Angular Accuracy × K_A = Degrees/sec²
K_A can be used to predict the output position error for a
given input acceleration. For example for an acceleration of
100 revs/sec², K_A = 2.7 × 10⁶ sec^–2 and 12-bit resolution.
Error in LSBs = ^{Input acceleration [LSB/sec2]}
K _A[sec ^–2 ]
=
100 [rev/sec ² ]
2.7 ×10⁶
×
2¹²
= 0.15 LSBs
or
47.5 seconds
of
arc
To determine the value of K_A based on the passive components
used to define the dynamics of the converter the following
should be used.
K
A
=
2ⁿ
•
4.04 ×10¹¹
R6• R4•(C4 +
C5)
Where n = resolution of the converter.
R4, R6 in ohms
C5, C4 in farads
–12–
REV. B