AD5398 Analog Devices, AD5398 Datasheet - Page 14

• Manufacturer Part Number: AD5398
• Description: 120 mA, Current Sinking, 10-Bit, I2C D/A Converter
• Manufacturer: Analog Devices

Specifications of AD5398

• Resolution (bits): 10bit
• Dac Update Rate: 31kSPS
• Dac Settling Time: 250µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: I2C/Ser 2-wire,Ser

AD5398
APPLICATIONS
The AD5398 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 22
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 mm, and the current through the motor in 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 approximately 10 μm/mA or less.
The AD5398 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 AD5398 the ideal solution
for these applications is the monotonicity of the device, which
ensures that lens positioning is repeatable for the application of
a given digital word.
Figure 23 shows a typical application circuit for the AD5398.
V
DD
R
P
R
P
I
2
C MASTER
DEVICE
SDA
SCL
I
2
DEVICE
C SLAVE
POWER-DOWN
I
2
DEVICE
RESET
C SLAVE
Figure 23. Typical Application Circuit
1
3
4
Rev. B | Page 14 of 16
INTERFACE
I
2
AD5398
C SERIAL
5
6
0.1μF
0.5
0.4
0.3
0.2
0.1
0
0
REFERENCE
OUTPUT DAC
Figure 22. Spring Preloaded Voice Coil Stroke vs. Sink Current
+
CURRENT
10
10-BIT
10μF
CURRENT
START
20
V
2
DD
30
R
40
SINK CURRENT (mA)
V
POWER-ON
50
CC
RESET
60
R
SENSE
+
70
3.3Ω
10μF
80
7
90
0.1μF
100 110 120
8
VOICE
COIL
ACTUATOR