EVAL-AD5398AEBZ AD [Analog Devices], EVAL-AD5398AEBZ Datasheet - Page 13

• Manufacturer Part Number: EVAL-AD5398AEBZ
• Description: 120 mA, Current Sinking, 10-Bit, I2C DAC
• Manufacturer: AD [Analog Devices]

APPLICATIONS INFORMATION
The AD5398A is designed to drive both spring preloaded
and nonspring linear motors used in applications such as lens
autofocus, image stabilization, or optical zoom. The operating
principle of the spring-preloaded motor is that the lens position
is controlled by the balancing of a voice coil and a spring. Figure 21
shows the transfer curve of a typical spring preloaded linear
motor for autofocus. The key points of this transfer function are
displacement or stroke, which is the actual distance the lens
moves in millimeters (mm), and the current through the motor
in milliamps (mA).
A start current is associated with spring-preloaded linear motors,
which is effectively 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 approxi-
mately 10 μm/mA or less.
The AD5398A 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 AD5398A the ideal
solution for these applications is the monotonicity of the device,
which ensures that lens positioning is repeatable for the applica-
tion of a given digital word.
Figure 22 shows a typical application circuit for the AD5398A.
V
DD
R
P
R
P
I
2
C MASTER
DEVICE
SDA
SCL
I
2
DEVICE
C SLAVE
POWER-DOWN
I
2
RESET
DEVICE
C SLAVE
Figure 22. Typical Application Circuit
SDA
SCL
PD
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AD5398A
INTERFACE
I
2
C SERIAL
V
DD
DGND
0.1µF
0.5
0.4
0.3
0.2
0.1
0
REFERENCE
OUTPUT DAC
+
0
CURRENT
Figure 21. Spring Preloaded Voice Coil Stroke vs. Sink Current
10-BIT
10µF
10
CURRENT
V
DD
START
DGND
20
30
R
V
POWER-ON
40
CC
RESET
SINK CURRENT (mA)
50
R
SENSE
+
3.3Ω
60
10µF
D1
AGND
70
V
DD
0.1µF
80
I
SINK
90
VOICE
COIL
ACTUATOR
100
110 120
AD5398