AD2S80 Analog Devices, AD2S80 Datasheet - Page 12

• Manufacturer Part Number: AD2S80
• Description: Variable Resolution/ Monolithic Resolver-to-Digital Converter
• Manufacturer: Analog Devices

AD2S80A
POSITION
OUTPUT
–135
–180
–12
180
135
–45
–90
Figure 6. AD2S80A Small Step Response
12
–3
–6
–9
90
45
9
6
3
0
0
0.02f
0.02f
BW
BW
Figure 5. AD2S80A Phase Plot
Figure 4. AD2S80A Gain Plot
t
0.04f
0.04f
1
BW
BW
0.1f
0.1f
BW
BW
FREQUENCY
FREQUENCY
t
2
0.2f
0.2f
BW
BW
0.4f
0.4f
BW
BW
f
f
BW
BW
2f
2f
BW
BW
TIME
–12–
The small signal step response is shown in Figure 6. The time
from the step to the first peak is t
the step until the converter is settled to 1 LSB. The times t
t
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 po-
sition 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
The numerator and denominator must have consistent angular
units. For example if K
may be specified in degrees/sec
Angular measurement may also be specified using radians, min-
utes of arc, LSBs, etc.
K
to it’s acceleration. The maximum acceleration allowable before
the converter loses track is dependent on the angular accuracy
requirements of the system.
K
given input acceleration. For example for an acceleration of
100 revs/sec
To determine the value of K
used to define the dynamics of the converter the following
should be used.
Where n = resolution of the converter.
2
A
A
are given approximately by
does not define maximum input acceleration, only the error due
can be used to predict the output position error for a
100 [rev/sec
Error in LSBs
2.7 10
R4, R6 in ohms
C5, C4 in farads
2
, K
Angular Accuracy
A
K
= 2.7
2
K
]
6
A
A
2
A
A
2
12
t
t
Error in Output Angle
1
is in sec
2
of the converter.
n
10
Input acceleration [LSB/sec
Input Acceleration
• R6• R4 •(C4 C5)
6
A
0.15 LSBs or 47.5 seconds of arc
f
sec
4.04 10
f
based on the passive components
BW
1
BW
2
5
and the error output in degrees.
-2
-2
1
K
, then the input acceleration
and the t
and 12-bit resolution.
A
K
= Degrees/sec
12
A
R
[sec
11
–2
2
is the time from
]
2
2
]
REV. A
1
and