AD2S90

REV. D

–10–

The small step response is given in Figure 20, and is the time

taken for the converter to settle to within 1 LSB.

ts = 7.00 ms (maximum)

The large step response (steps >20

°) applies when the error

voltage will exceed the linear range of the converter. Typically it

will take three times longer to reach the first peak for a 179

°

step.

In response to a velocity step [VELOUT/(d

θ/dt)] the velocity

output will exhibit the same response characteristics as outlined

above.

0

10

20

016

4

812

Figure 20. Small Step Response

SOURCES OF ERROR

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

Input Acceleration

Error in Output Angle

(10)

does not define maximum input acceleration, only the error due to

its acceleration. The maximum acceleration allowable before the

converter loses track is dependent on the angular accuracy

requirements of the system.

Angular Error

× K

2

(11)

6

sec

can be calculated as follows:

Error in LSBs

=

Input Acceleration LSB / sec

2

[]

2

[]

=

×

[]

=

100

2

30 10

014

12

62

rev

LSB rev

LSBs

//

.

sec

.

–

(12)