Datasheet

AD5821A
Rev. 0 | Page 14 of 16
APPLICATIONS INFORMATION
The AD5821A is designed to drive both spring-preloaded and
nonspring linear motors used in applications such as lens auto-
focus, image stabilization, or optical zoom. The operation principle
of the spring-preloaded motor is that the lens position is controlled
by the balancing of a voice coil and spring. Figure 25 shows the
transfer curve of a typical spring-preloaded linear motor for
autofocus. The key points of this transfer function are displace-
ment or stroke, which is the actual distance the lens moves in
millimeters (mm) and the current through the motor, measured
in milliamps (mA).
A start current is associated with spring-preloaded linear
motors, which is a threshold current that must be exceeded for
any displacement in the lens to occur. The start current is usually
20 mA or greater; the rated stroke or displacement is usually
0.25 mm to 0.4 mm; and the slope of the transfer curve is
approximately 10 µm/mA or less.
The AD5821A is designed to sink up to 120 mA, which is more
than adequate for available commercial linear motors or voice
coils. Another factor that makes the AD5821A the ideal solu-
tion for these applications is the monotonicity of the device,
ensuring that lens positioning is repeatable for the application
of a given digital word.
Figure 26 shows a typical application circuit for the AD5821A.
10 50 60 8070 90 100403020 110 120
0.1
0.5
0.4
0.3
0.2
START
CURRENT
SINK CURRENT (mA)
STROKE (mm)
07796-029
Figure 25. Spring-Preloaded Voice Coil Stroke vs. Sink Current
7
2
1
XSHUTDOWN
8
VOICE
COIL
I
SINK
R
SENSE
REFERENCE
R
AD5821A
5
SCL
SDA
I
2
C MASTER
DEVICE
I
2
C SLAVE
DEVICE
R
P
R
P
V
DD
V
CC
V
DD
D1
0.1µF
I
2
C SERIAL
INTERFACE
3
4
6
POWER-ON
RESET
0.1µF 10µF
10µF
+
+
V
CC
V
DD
10-BIT
CURRENT
OUTPUT DAC
07796-028
Figure 26. Typical Application Circuit