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參數資料
| 型號： | AD7769 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | LC2MOS Analog I/O Port |
| 中文描述： | LC2MOS模擬I / O端口 |
| 文件頁數： | 15/16頁 |
| 文件大小： | 265K |
| 代理商： | AD7769 |
AD7769
–15–
REV. A
Figure 28. Generating a Software Programmable V
SWING
(DAC)
For example, with a fixed input swing voltage of 2.5 V, the pro-
grammable span via DAC B is as follows:
D
B
= 0:
V
SWING
(DAC) = 2.08
D
B
= 1/2: V
SWING
(DAC) = 2.5 V = V
SWING
D
B
≈
1:
V
SWING
(DAC) = 3.125 V
T he AD7769 is specified for a V
SWING
(DAC) voltage range
from 2 V to 3 V, although in practice this range can be extended
while still maintaining monotonic operation.
Closed Loop Microstepping
Microstepping is a popular technique in low density disk drives
(both floppy
and hard disk) that allows higher positional resolu-
tion of the disk drive head over that obtainable from a full-step
driven stepper motor. T ypically, a two-phase stepper motor has
its phase currents driven with a sine-cosine relationship. T hese
cosinusoidal signals are generated by two DACs driven with the
appropriate data. T he resolution of the DACs determines the
number of microsteps into which each full step can be divided.
For example, with a 1.8
°
full-step motor and a 4-bit DAC, a
microstep size of 0.11
°
(1.8
°
/2
n
) is obtainable.
T he microstepping technique improves the positioning resolu-
tion possible in any control application. However, the positional
accuracy can be significantly worse than that offered by the orig-
inal full-step accuracy specification due to load torque effects.
T o ensure that the increased resolution is usable, it is therefore
necessary to use a closed-loop system where the position of the
disk drive head (or motor) is monitored. T he closed-loop system
allows an error between the desired position and the actual posi-
tion to be monitored and corrected. T he correction is achieved
by adjusting the ratio of the phase currents in the motor wind-
ings until the required head position is reached.
T he AD7769 is ideally suited for the closed-loop microstepping
technique with its dual DACs for positioning the disk drive
head and dual channel ADC for monitoring the position of the
head. A typical circuit for a closed-loop microstepping system is
shown in Figure 29. T he DAC waveforms are shown in Figure
30 along with the direction information of clockwise rotation
supplied by the controller.
Figure 29. Typical Closed-Loop Microstepping Circuit
with the AD7769
Figure 30. Typical Control Waveforms for the Microstep-
ping Circuit of Figure 29
A typical transducer would be a moire-fringe transducer which
consists of two gratings, one fixed and one moveable. T he rela-
tive positions of these two gratings will modulate the amount of
light from a LED which can pass through. In order to derive
head direction information the stationary grating has two sets of
bars, with a 90
°
phase relationship, and two photo-transistors.
T he quadrature sinusoidal output waveforms (N & Q) can be
converted directly by the AD7769.
相關PDF資料 |
PDF描述 |
|---|---|
| AD7769AN | LC2MOS Analog I/O Port |
| AD7769AP | LC2MOS Analog I/O Port |
| AD7769JN | LC2MOS Analog I/O Port |
| AD7769JP | LC2MOS Analog I/O Port |
| AD7773 | LC MOS COMPLETE EMBEDDED SERVO FRONT ENDS FOR HDD |
相關代理商/技術參數 |
參數描述 |
|---|---|
| AD7769AN | 制造商:AD 制造商全稱:Analog Devices 功能描述:LC2MOS Analog I/O Port |
| AD7769AP | 制造商:AD 制造商全稱:Analog Devices 功能描述:LC2MOS Analog I/O Port |
| AD7769JN | 制造商:AD 制造商全稱:Analog Devices 功能描述:LC2MOS Analog I/O Port |
| AD7769JP | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| AD7769JP-REEL | 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
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