120 mA, Current Sinking, 10-Bit, I C DAC

120 mA, Current Sinking,
10-Bit, I2C® DAC
AD5821
FEATURES
INDUSTRIAL APPLICATIONS
120 mA current sink
Available in 3 × 3 array WLCSP package
2-wire (I2C-compatible) 1.8 V serial interface
10-bit resolution
Integrated current sense resistor
2.7 V to 5.5 V power supply
Guaranteed monotonic over all codes
Power-down to 0.5 μA typical
Internal reference
Ultralow noise preamplifier
Power-down function
Power-on reset
Heater controls
Fan controls
Cooler (Peltier) controls
Solenoid controls
Valve controls
Linear actuator controls
Light controls
Current loop controls
GENERAL DESCRIPTION
The AD5821 is a single 10-bit digital-to-analog converter with
120 mA output current sink capability. It features an internal
reference and operates from a single 2.7 V to 5.5 V supply.
The DAC is controlled via a 2-wire (I2C-compatible) serial
interface that operates at clock rates up to 400 kHz.
CONSUMER APPLICATIONS
Lens autofocus
Image stabilization
Optical zoom
Shutters
Iris/exposure
Neutral density (ND) filters
Lens covers
Camera phones
Digital still cameras
Camera modules
Digital video cameras/camcorders
Camera-enabled devices
Security cameras
Web/PC cameras
The AD5821 incorporates a power-on reset circuit that ensures
that the DAC output powers up to 0 V and remains there until
a valid write takes place. It has a power-down feature that reduces
the current consumption of the device to 1 μA maximum.
The AD5821 is designed for autofocus, image stabilization, and
optical zoom applications in camera phones, digital still cameras,
and camcorders.
The AD5821 also has many industrial applications, such as
controlling temperature, light, and movement, over the range of
−40°C to +85°C without derating.
The I2C address for the AD5821 is 0x18.
FUNCTIONAL BLOCK DIAGRAM
VDD
XSHUTDOWN
DGND
REFERENCE
POWER-ON
RESET
D1
I2C SERIAL
INTERFACE
10-BIT
CURRENT
OUTPUT DAC
ISINK
R
AD5821
RSENSE
3.3Ω
AGND
DGND
05950-001
SDA
SCL
VDD
Figure 1.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2007 Analog Devices, Inc. All rights reserved.
AD5821
TABLE OF CONTENTS
Features .............................................................................................. 1
Typical Performance Characteristics ..............................................7
Consumer Applications ................................................................... 1
Terminology .................................................................................... 10
Industrial Applications .................................................................... 1
Theory of Operation ...................................................................... 11
General Description ......................................................................... 1
Serial Interface ............................................................................ 11
Functional Block Diagram .............................................................. 1
I2C Bus Operation ...................................................................... 11
Revision History ............................................................................... 2
Data Format ................................................................................ 11
Specifications..................................................................................... 3
Power Supply Bypassing and Grounding................................ 12
AC Specifications.......................................................................... 4
Applications Information .............................................................. 14
Timing Specifications .................................................................. 4
Outline Dimensions ....................................................................... 15
Absolute Maximum Ratings............................................................ 5
Ordering Guide .......................................................................... 15
Pin Configuration and Function Descriptions............................. 6
REVISION HISTORY
1/07—Revision 0: Initial Version
Rev. 0 | Page 2 of 16
AD5821
SPECIFICATIONS
VDD = 2.7 V to 5.5 V, AGND = DGND = 0 V, load resistance RL = 25 Ω connected to VDD; all specifications TMIN to TMAX,
unless otherwise noted.
Table 1.
Parameter
DC PERFORMANCE
Resolution
Relative Accuracy 2
Differential Nonlinearity2, 3
Zero-Code Error2, 4
Offset Error @ Code 162
Gain Error2
Offset Error Drift4, 5
Gain Error Drift2, 5
OUTPUT CHARACTERISTICS
Minimum Sink Current4
Maximum Sink Current
Output Current During XSHUTDOWN
Output Compliance5
Output Compliance5
Power-Up Time
LOGIC INPUTS (XSHUTDOWN)5
Input Current
Input Low Voltage, VINL
Input High Voltage, VINH
Pin Capacitance
LOGIC INPUTS (SCL, SDA)5
Input Low Voltage, VINL
Input High Voltage, VINH
Input Low Voltage, VINL
Input High Voltage, VINH
Input Leakage Current, IIN
Input Hysteresis, VHYST
Digital Input Capacitance, CIN
Glitch Rejection 6
POWER REQUIREMENTS
VDD
IDD (Normal Mode)
VDD = 2.7 V to 3.6 V
IDD (Power-Down Mode) 7
Min
B Version 1
Typ
Max
10
±1.5
Unit
±0.5
Bits
LSB
LSB
mA
mA
% of FSR
μA/°C
LSB/°C
0.6
VDD
mA
mA
nA
V
0.48
VDD
V
0
1
0.5
±4
±1
5
±0.6
10
±0.2
3
120
80
20
μs
±1
0.54
μA
V
V
pF
+0.54
VDD + 0.3
+0.54
VDD + 0.3
±1
50
V
V
V
V
μA
V
pF
ns
5.5
V
4
mA
μA
1.3
3
−0.3
1.26
−0.3
1.4
0.05 VDD
6
2.7
2.5
0.5
1
Test Conditions/Comments
VDD = 3.6 V to 4.5 V; device operates over 2.7 V to 5.5 V
with reduced performance
117 μA/LSB
Guaranteed monotonic over all codes
All 0s loaded to DAC
@ 25°C
XSHUTDOWN = 0
Output voltage range over which maximum 120 mA
sink current is available
Output voltage range over which 90 mA sink current
is available
To 10% of FS, coming out of power-down mode; VDD = 5 V
VDD = 2.7 V to 5.5 V
VDD = 2.7 V to 5.5 V
VDD = 2.7 V to 3.6 V
VDD = 2.7 V to 3.6 V
VDD = 3.6 V to 5.5 V
VDD = 3.6 V to 5.5 V
VIN = 0 V to VDD
Pulse width of spike suppressed
IDD specification is valid for all DAC codes
VINH = 1.8 V, VINL = GND, VDD = 3.6 V
VINH = 1.8 V, VINL = GND
Temperature range is as follows: B Version = −30°C to +85°C.
See the Terminology section.
3
Linearity is tested using a reduced code range: Code 32 to Code 1023.
4
To achieve near zero output current, use the power-down feature.
5
Guaranteed by design and characterization; not production tested. XSHUTDOWN is active low. SDA and SCL pull-up resistors are tied to 1.8 V.
6
Input filtering on both the SCL and the SDA inputs suppresses noise spikes that are less than 50 ns.
7
XSHUTDOWN is active low.
2
Rev. 0 | Page 3 of 16
AD5821
AC SPECIFICATIONS
VDD = 2.7 V to 5.5 V, AGND = DGND = 0 V, load resistance RL = 25 Ω connected to VDD, unless otherwise noted.
Table 2.
Parameter
Output Current Settling Time
Slew Rate
Major Code Change Glitch Impulse
Digital Feedthrough 3
1
2
3
B Version 1, 2
Min Typ Max
250
0.3
0.15
0.06
Unit
μs
mA/μs
nA-s
nA-s
Test Conditions/Comments
VDD = 3.6 V, RL = 25 Ω, LL = 680 μH, ¼ scale to ¾ scale change (0x100 to 0x300)
1 LSB change around major carry
Temperature range is as follows: B Version = −40°C to +85°C.
Guaranteed by design and characterization; not production tested.
See the Terminology section.
TIMING SPECIFICATIONS
VDD = 2.7 V to 3.6 V. All specifications TMIN to TMAX, unless otherwise noted.
Table 3.
B Version
Limit at TMIN, TMAX
400
2.5
0.6
1.3
0.6
100
0.9
0
0.6
0.6
1.3
300
0
250
300
20 + 0.1 CB 3
400
Parameter 1
fSCL
t1
t2
t3
t4
t5
t6 2
t7
t8
t9
t10
t11
CB
1
2
3
Unit
kHz max
μs min
μs min
μs min
μs min
ns min
μs max
μs min
μs min
μs min
μs min
ns max
ns min
ns max
ns max
ns min
pF max
Description
SCL clock frequency
SCL cycle time
tHIGH, SCL high time
tLOW, SCL low time
tHD, STA, start/repeated start condition hold time
tSU, DAT, data setup time
tHD, DAT, data hold time
tSU, STA, setup time for repeated start
tSU, STO, stop condition setup time
tBUF, bus free time between a stop condition and a start condition
tR, rise time of both SCL and SDA when receiving
May be CMOS driven
tF, fall time of SDA when receiving
tF, fall time of both SCL and SDA when transmitting
Capacitive load for each bus line
Guaranteed by design and characterization; not production tested.
A master device must provide a hold time of at least 300 ns for the SDA signal (referred to the VINH MIN of the SCL signal) to bridge the undefined region of the SCL falling edge.
CB is the total capacitance of one bus line in pF. tR and tF are measured between 0.3 VDD and 0.7 VDD.
Timing Diagram
SDA
t3
t9
t10
t4
t11
SCL
t6
t2
t7
t5
REPEATED
START
CONDITION
Figure 2. 2-Wire Serial Interface Timing Diagram
Rev. 0 | Page 4 of 16
t1
t8
STOP
CONDITION
05950-002
t4
START
CONDITION
AD5821
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 4.
Parameter
VDD to AGND
VDD to DGND
AGND to DGND
SCL, SDA to DGND
XSHUTDOWN to DGND
ISINK to AGND
Operating Temperature Range
Industrial (B Version)
Storage Temperature Range
Junction Temperature (TJ MAX)
WLFCSP Power Dissipation
θJA Thermal Impedance 1
Mounted on 4-Layer Board
Lead Temperature, Soldering
Maximum Peak Reflow Temperature 2
Rating
–0.3 V to +5.5 V
–0.3 V to VDD + 0.3 V
–0.3 V to +0.3 V
–0.3 V to VDD + 0.3 V
–0.3 V to VDD + 0.3 V
–0.3 V to VDD + 0.3 V
−30°C to +85°C
−65°C to +150°C
150°C
(TJ MAX − TA)/θJA
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
95°C/W
260°C (±5°C)
1
To achieve the optimum θJA, it is recommended that the AD5821
be soldered on a 4-layer board.
2
As per JEDEC J-STD-020C.
Rev. 0 | Page 5 of 16
AD5821
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
3
2
1
A
C
VIEW FROM BALL SIDE
05950-021
B
Figure 3. 9-Ball WLCSP Pin Configuration
Table 5. 9-Ball WLCSP Pin Function Description
Mnemonic
ISINK
NC
XSHUTDOWN
AGND
DGND
SDA
DGND
VDD
SCL
Description
Output Current Sink.
No Connection.
Power-Down. Asynchronous power-down signal, active low.
Analog Ground Pin.
Digital Ground Pin.
I2C Interface Signal.
Digital Ground Pin.
Digital Supply Voltage.
I2C Interface Signal.
1515µm
NC
ISINK
8
XSHUTDOWN
1
AGND
7
DGND
2
1690µm
SDA
3
VDD
6
SCL
4
DGND
5
05950-030
Ball Number
A1
A2
A3
B1
B2
B3
C1
C2
C3
Figure 4. Metallization Photo
Dimensions shown in microns (μm)
Rev. 0 | Page 6 of 16
AD5821
TYPICAL PERFORMANCE CHARACTERISTICS
2.0
VERT = 50μs/DIV
INL VDD = 3.8V
TEMP = 25°C
INL (LSB)
1.5
1.0
0.5
3
952
CODE
Figure 5. Typical INL vs. Code Plot
0.6
M50.0μs
Figure 8. Settling Time for a 4-LSB Step (VDD = 3.6 V)
DNL VDD = 3.8V
TEMP = 25°C
0.5
05034-007
HORIZ = 468μA/DIV
CH3
1008
1023
896
840
784
728
672
616
560
504
448
392
336
280
224
168
112
0
56
–0.5
05034-004
0
VERT = 2μA/DIV
4.8μA p-p
0.4
DNL (LSB)
0.3
0.2
1
0.1
0
HORIZ = 2s/DIV
CH1
1008
1023
CODE
952
896
840
784
728
672
616
560
504
448
392
336
280
224
168
112
0
56
–0.3
05034-005
–0.2
05034-008
–0.1
M2.0s
Figure 9. 0.1 Hz to 10 Hz Noise Plot (VDD = 3.6 V)
Figure 6. Typical DNL vs. Code Plot
92.0
0.14
91.5
0.12
IOUT @ +25°C
0.10
IOUT (A)
90.5
90.0
IOUT @ +85°C
0.08
0.06
89.5
0.04
89.0
Figure 7. ¼ to ¾ Scale Settling Time (VDD = 3.6 V)
05034-009
952
896
840
784
728
672
1008
1023
CODE
616
560
504
448
392
336
0
300.0–6 333.1–6
280
250.0–6
224
200.0–6
TIME
168
150.0–6
112
100.0–6
0
88.0
53.5–6
0.02
56
88.5
05034-006
OUTPUT CURRENT (mA)
IOUT @ –40°C
91.0
Figure 10. Sink Current vs. Code vs. Temperature (VDD = 3.6 V)
Rev. 0 | Page 7 of 16
AD5821
2000
0.45
1800
0.40
1600
0.35
ZERO-CODE ERROR (mA)
VDD = 3.6V
1400
1000
800
600
400
100
1k
FREQUENCY
10k
NEGATIVE INL (VDD = 3.6V)
NEGATIVE INL (VDD = 3.8V)
NEGATIVE INL (VDD = 4.5V)
55
65
75
85
–40 –30 –20 –10
0 15 25 35 45
TEMPERATURE (°C)
55
65
75
VDD = 3.8V
0
–0.5
–1.0
–2.0
85
VDD = 3.6V
–40 –30 –20 –10
1.0
1.4
1.3 VDD = 5.5V
1.2
0.6
POSITIVE DNL (VDD = 3.6V)
1.1
VOLTAGE (V)
POSITIVE DNL (VDD = 4.5V)
0.2
NEGATIVE DNL (VDD = 3.8V)
15
25
35
45
55
65
75
85
Figure 15. Full-Scale Error vs. Temperature vs. Supply Voltage
0.8
0
0
TEMPERATURE (°C)
Figure 12. INL vs. Temperature vs. Supply Voltage
POSITIVE DNL (VDD = 3.8V)
1.0
VDD = 4.5V
VDD = 3.6V
VDD = 2.7V
0.9
0.8
0.7
–0.4
0.6
NEGATIVE DNL (VDD = 4.5V)
NEGATIVE DNL (VDD = 3.6V)
–40 –30 –20 –10
0 15 25 35 45
TEMPERATURE (°C)
0.5
05034-012
–1.0
45
0.5
–1.5
05034-011
–0.5
–0.8
35
05950-014
FULL-SCALE ERROR (mA)
POSITIVE INL (VDD = 3.6V)
1.0
–0.6
25
VDD = 4.5V
1.5
–0.2
15
1.0
POSITIVE INL (VDD = 4.5V)
2.0
0.4
0
Figure 14. Zero-Code Error vs. Supply Voltage vs. Temperature
2.5
INL (LSB)
–40 –30 –20 –10
1.5
POSITIVE INL (VDD = 3.8V)
DNL (LSB)
0.10
TEMPERATURE (°C)
3.0
–1.0
0.15
0
3.5
0
0.20
100k
Figure 11. AC Power Supply Rejection (VDD = 3.6 V)
0.5
VDD = 3.8V
05950-013
0
10
VDD = 4.5V
0.25
0.05
05034-010
200
0.30
55
65
75
05950-024
μA/V
1200
0.4
–50
85
–30
–10
10
30
50
70
TEMPERATURE (°C)
Figure 16. SCL and SDA Logic High Level (VINH) vs.
Supply Voltage and Temperature
Figure 13. DNL vs. Temperature vs. Supply Voltage
Rev. 0 | Page 8 of 16
90
1.4
1.4
1.3
1.3
1.2
1.2
1.1
1.1
1.0
1.0
VDD = 5.5V
VDD = 4.5V
0.8
0.7
VDD = 2.7V
0.5
–10
10
30
50
70
0.4
–50
90
VDD = 5.5V
VDD = 4.5V
VDD = 3.6V
0.9
0.8
0.7
0.6
05950-025
VOLTAGE (V)
VDD = 2.7V
1.0
0.5
0.4
–50
–30
–10
10
30
–30
–10
10
30
50
70
Figure 19. DNL vs. XSHUTDOWN Logic Low Level (VINL) vs.
Supply Voltage and Temperature
1.4
1.1
VDD = 2.7V
TEMPERATURE (°C)
Figure 17. SCL and SDA Logic Low Level (VINL) vs.
Supply Voltage and Temperature
1.2
VDD = 3.6V
0.5
TEMPERATURE (°C)
1.3
0.8
0.6
05950-026
0.6
–30
VDD = 4.5V
0.9
0.7
VDD = 3.6V
0.4
–50
VDD = 5.5V
05950-027
0.9
VOLTAGE (V)
VOLTAGE (V)
AD5821
50
70
90
TEMPERATURE (°C)
Figure 18. XSHUTDOWN Logic High Level (VINH) vs.
Supply Voltage and Temperature
Rev. 0 | Page 9 of 16
90
AD5821
TERMINOLOGY
Relative Accuracy
For the DAC, relative accuracy or integral nonlinearity is a
measurement of the maximum deviation, in LSB, from a
straight line passing through the endpoints of the DAC transfer
function. A typical INL vs. code plot is shown in Figure 5.
Differential Nonlinearity (DNL)
Differential nonlinearity is the difference between the measured
change and the ideal 1 LSB change between any two adjacent
codes. A specified differential nonlinearity of ±1 LSB maximum
ensures monotonicity. This DAC is guaranteed monotonic by
design. A typical DNL vs. code plot is shown in Figure 6.
Zero-Code Error
Zero-code error is a measurement of the output error when zero
code (0x0000) is loaded to the DAC register. Ideally, the output
is 0 mA. The zero-code error is always positive in the AD5821
because the output of the DAC cannot go below 0 mA. This is
due to a combination of the offset errors in the DAC and output
amplifier. Zero-code error is expressed in milliamperes (mA).
Gain Error
Gain error is a measurement of the span error of the DAC. It is
the deviation in slope of the DAC transfer characteristic from
the ideal, expressed as a percent of the full-scale range.
Gain Error Drift
Gain error drift is a measurement of the change in gain error
with changes in temperature. It is expressed in LSB/°C.
Digital-to-Analog Glitch Impulse
This is the impulse injected into the analog output when the
input code in the DAC register changes state. It is normally
specified as the area of the glitch in nanoamperes per second
(nA-s) and is measured when the digital input code is changed
by 1 LSB at the major carry transition.
Digital Feedthrough
Digital feedthrough is a measurement of the impulse injected
into the analog output of the DAC from the digital inputs of the
DAC, but it is measured when the DAC output is not updated.
It is specified in nanoamperes per second (nA-s) and measured
with a full-scale code change on the data bus, that is, from all 0s
to all 1s and vice versa.
Offset Error
Offset error is a measurement of the difference between ISINK
(actual) and IOUT (ideal) in the linear region of the transfer
function, expressed in milliamperes (mA). Offset error is
measured on the AD5821 with Code 16 loaded into the DAC
register.
Offset Error Drift
Offset error drift is a measurement of the change in offset error
with a change in temperature. It is expressed in microvolts per
degree Celsius (μV/°C).
Rev. 0 | Page 10 of 16
AD5821
THEORY OF OPERATION
The AD5821 is a fully integrated, 10-bit digital-to-analog
converter (DAC) with 120 mA output current sink capability.
It is intended for driving voice coil actuators in applications
such as lens autofocus, image stabilization, and optical zoom.
The circuit diagram is shown in Figure 20. A 10-bit current
output DAC coupled with Resistor R generates the voltage that
drives the noninverting input of the operational amplifier. This
voltage also appears across the RSENSE resistor and generates the
sink current required to drive the voice coil.
When the bus is idle, SCL and SDA are both high. The master
device initiates a serial bus operation by generating a start
condition, which is defined as a high-to-low transition on the
SDA low while SCL is high. The slave device connected to the
bus responds to the start condition and shifts in the next eight
data bits under control of the serial clock. These eight data bits
consist of a 7-bit address, plus a read/write (R/W) bit that is 0 if
data is to be written to a device, and 1 if data is to be read from a
device. Each slave device on an I2C bus must have a unique address.
The address of the AD5821 is 0001100; however, 0001101,
0001110, and 0001111 address the part because the last two bits
are unused/don’t cares (see Figure 22 and Figure 23). Because the
address plus the R/W bit always equals eight bits of data, the write
address of the AD5821 is 00011000 (0x18) and the read address
is 00011001 (0x19) (see Figure 22 and Figure 23).
Resistor R and Resistor RSENSE are interleaved and matched.
Therefore, the temperature coefficient and any nonlinearities
over temperature are matched, and the output drift over temperature is minimized. Diode D1 is an output protection diode.
VDD
XSHUTDOWN
DGND
REFERENCE
POWER-ON
RESET
VDD
D1
10-BIT
CURRENT
OUTPUT DAC
I2C SERIAL
INTERFACE
SCL
ISINK
RSENSE
3.3Ω
R
AD5821
05950-001
SDA
AGND
DGND
Figure 20. Block Diagram Showing Connection to Voice Coil
SERIAL INTERFACE
The AD5821 is controlled using the industry-standard I2C
2-wire serial protocol. Data can be written to or read from the
DAC at data rates of up to 400 kHz. After a read operation, the
contents of the input register are reset to all 0s.
I2C BUS OPERATION
An I2C bus operates with one or more master devices that
generate the serial clock (SCL) and read and write data on the
serial data line (SDA) to and from slave devices such as the
AD5821. All devices on an I2C bus have their SDA pin connected
to the SDA line and their SCL pin connected to the SCL line of
the master device. I2C devices can only pull the bus lines low;
pulling high is achieved by pull-up resistors, RP. The value of RP
depends on the data rate, bus capacitance, and the maximum load
current that the I2C device can sink (3 mA for a standard device).
1.8V
RP
I2C data is divided into blocks of eight bits, and the slave generates
an ACK at the end of each block. Because the AD5821 requires
10 bits of data, two data-words must be written to it when a
write operation occurs, or read from it when a read operation
occurs. At the end of a read or write operation, the AD5821
acknowledges the second data byte. The master generates a stop
condition, defined as a low-to-high transition on SDA while SCL
is high, to end the transaction.
DATA FORMAT
Data is written to the AD5821 high byte first, MSB first, and is
shifted into the 16-bit input register. After all data is shifted in,
data from the input register is transferred to the DAC register.
Because the DAC requires only 10 bits of data, not all bits of the
input register data are used. The MSB is reserved for an activehigh, software-controlled, power-down function. Bit 14 is unused;
Bit 13 to Bit 4 correspond to the DAC data bits, Bit 9 to Bit 0.
Bit 3 to Bit 0 are unused.
During a read operation, data is read in the same bit order.
SDA
SCL
I2C MASTER
DEVICE
I2C SLAVE
DEVICE
AD5821
I2C SLAVE
DEVICE
05950-016
RP
At the end of the address data, after the R/W bit, the slave
device that recognizes its own address responds by generating
an acknowledge (ACK) condition. This is defined as the slave
device pulling SDA low while SCL is low before the ninth clock
pulse and keeping it low during the ninth clock pulse. Upon
receiving ACK, the master device can clock data into the AD5821
in a write operation, or it can clock it out in a read operation.
Data must change either during the low period of the clock
(because SDA transitions during the high period define a start
condition, as described previously), or during a stop condition,
as described in the Data Format section.
Figure 21. Typical I2C Bus
Rev. 0 | Page 11 of 16
AD5821
1
9
1
9
1
SCL
0
0
0
1
1
1
1
R/W
START BY
MASTER
PD
X
D9
D8
D7
D6
D5
D4
ACK BY
AD5821
D3
D2
D1
D0
X
X
X
X
ACK BY
AD5821
ACK BY
AD5821
FRAME 3
LEAST SIGNIFICANT
DATA BYTE
FRAME 2
MOST SIGNIFICANT
DATA BYTE
FRAME 1
SERIAL BUS
ADDRESS BYTE
STOP BY
MASTER
05950-017
SDA
Figure 22. Write Operation
1
9
1
1
9
SCL
0
0
0
1
1
1
1
R/W
START BY
MASTER
PD
X
D9
D8
D7
D6
D5
D4
ACK BY
AD5821
D3
D2
D1
D0
X
X
X
X
ACK BY
AD5821
FRAME 1
SERIAL BUS
ADDRESS BYTE
ACK BY
AD5821
FRAME 2
MOST SIGNIFICANT
DATA BYTE
STOP BY
MASTER
FRAME 3
LEAST SIGNIFICANT
DATA BYTE
05950-018
SDA
Figure 23. Read Operation
Table 6. Data Format 1
Serial Data-Words
Serial Data Bits
Input Register
Function
1
High Byte
SD7
R15
XSHUTDOWN
SD6
R14
X
SD5
R13
D9
SD4
R12
D8
SD3
R11
D7
SD2
R10
D6
SD1
R9
D5
SD0
R8
D4
Low Byte
SD7 SD6
R7
R6
D3
D2
SD5
R5
D1
SD4
R4
D0
SD3
R3
X
SD2
R2
X
SD1
R1
X
SD0
R0
X
XSHUTDOWN = soft power-down; X = unused/don’t care; and D9 to D0 = DAC data.
VBATTERY
POWER SUPPLY BYPASSING AND GROUNDING
VOICE
COIL
When accuracy is important in an application, it is beneficial to
consider power supply and ground return layout on the PCB.
The PCB for the AD5821 should have separate analog and digital
power supply sections. Where shared AGND and DGND is
necessary, the connection of grounds should be made at only
one point, as close as possible to the AD5821.
VCOIL
RC
VDD
AD5821
DGND
RT
TRACE
RESISTANCE
ISINK
Q1
SDA
SCL
R
VDROP
RSENSE
XSHUTDOWN
Rev. 0 | Page 12 of 16
AGND
DGND
RG
LG
GROUND
RETURN
Figure 24. Effect of PCB Trace Resistance and Inductance
05950-019
Special attention should be paid to the layout of the AGND return
path and, and it should be tracked between the voice coil motor
and ISINK to minimize any series resistance. Figure 24 shows the
output current sink of the AD5821 and illustrates the importance
of reducing the effective series impedance of AGND and the track
resistance between the motor and ISINK. The voice coil is modeled
as Inductor LC and Resistor RC. The current through the voice coil
is effectively a dc current that results in a voltage drop, VC, when
the AD5821 is sinking current. The effect of any series inductance
is minimal.
LC
AD5821
When sinking the maximum current of 120 mA, the maximum
voltage drop allowed across RSENSE is 400 mV, and the minimum
drain to source voltage of Q1 is 200 mV. This means that the
AD5821 output has a compliance voltage of 600 mV. If VDROP
falls below 600 mV, the output transistor, Q1, can no longer
operate properly and ISINK may not be maintained as a constant.
When sinking 90 mA, the maximum voltage drop allowed
across RSENSE is 300 mV, and the minimum drain to source
voltage of Q1 is 180 mV. This means that the AD5821 output
has a compliance voltage of 480 mV. If VDROP falls below 480 mV,
the output transistor, Q1, can no longer operate properly and
ISINK may not be maintained as a constant. As ISINK decreases, the
voltage required across the transistor, Q1, also decreases and,
therefore, lower supplies can be used with the voice coil motor.
As the current increases to 120 mA through the voice coil,
VC increases. VDROP decreases and eventually approaches the
minimum specified compliance voltage of 600 mV (or 480 mV,
if ISINK = 90 mA). The ground return path is modeled by the
components RG and LG. The track resistance between the voice
coil and the AD5821 is modeled as RT. The inductive effects of
LG influence RSENSE and RC equally, and because the current is
maintained as a constant, it is not as critical as the purely resistive
component of the ground return path. When the maximum sink
current is flowing through the motor, the resistive elements, RT and
RG, may have an impact on the voltage headroom of Q1 and
could, in turn, limit the maximum value of RC because of
voltage compliance.
For example, if
VBATTERY = 3.6 V
RG = 0.5 Ω
RT = 0.5 Ω
ISINK = 120 mA
VDROP = 600 mV (the compliance voltage)
Then the largest value of resistance of the voice coil, RC, is
RC =
VBAT − [VDROP + ( I SINK × RT ) + ( I SINK × RG )]
=
I SINK
3.6 V − [600 mV + 2 × (120 mA × 0.5 Ω)]
120 mA
= 24 Ω
Using another example, if
VBATTERY = 3.6 V
RG = 0.5 Ω
RT = 0.5 Ω
ISINK = 90 mA
VDROP = 480 mV (the compliance voltage specification at 90 mA)
Then the largest value of resistance of the voice coil, RC, is
RC =
VBAT − [VDROP + ( I SINK × RT ) + ( I SINK × RG )]
=
I SINK
3.6 V − [480 mV + 2 × (90 mA × 0.5 Ω)]
90 mA
= 33.66 Ω
For this reason, it is important to minimize any series impedance
on both the ground return path and interconnect between the
AD5821 and the motor. It is also important to note that for
lower values of ISINK, the compliance voltage of the output stage
also decreases. This decrease allows the user to either use voice
coil motors with high resistance values or decrease the power
supply voltage on the voice coil motor. The compliance voltage
decreases as the ISINK current decreases.
The power supply of the AD5821, or the regulator used to supply
the AD5821, should be decoupled. Best practice power supply
decoupling recommends that the power supply be decoupled
with a 10 μF capacitor. Ideally, this 10 μF capacitor should be of
a tantalum bead type. However, if the power supply or regulator
supply is well regulated and clean, such decoupling may not be
required. The AD5821 should be decoupled locally with a 0.1 μF
ceramic capacitor, and this 0.1 μF capacitor should be located as
close as possible to the VDD pin. The 0.1 μF capacitor should be
ceramic with a low effective series resistance and effective series
inductance. The 0.1 μF capacitor provides a low impedance path
to ground for high transient currents.
The power supply line should have as large a trace as possible to
provide a low impedance path and reduce glitch effects on the
supply line. Clocks and other fast switching digital signals should
be shielded from other parts of the board by digital ground.
Avoid crossover of digital and analog signals, if possible. When
traces cross on opposite sides of the board, they should run at
right angles to each other to reduce feedthrough effects through
the board. The best technique is to use a multilayer board with
ground and power planes, where the component side of the
board is dedicated to the ground plane only and the signal
traces are placed on the solder side. However, this is not always
possible with a 2-layer board.
Rev. 0 | Page 13 of 16
AD5821
APPLICATIONS INFORMATION
0.5
0.4
STROKE (mm)
0.3
0.2
START
CURRENT
0.1
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.
10
20
30
40
50
60
70
80
90 100 110 120
SINK CURRENT (mA)
Figure 25. Spring-Preloaded Voice Coil Stroke vs. Sink Current
The AD5821 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 AD5821 the ideal solution
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 AD5821.
VDD
VCC
0.1µF
2
6
VDD
RP
RP
SDA
3
SCL
I2C MASTER
DEVICE
REFERENCE
1
4
I2C SERIAL
INTERFACE
I2C SLAVE
DEVICE
POWER-ON
RESET
VOICE
COIL
D1
10-BIT
CURRENT
OUTPUT DAC
8
ISINK
RSENSE
R
AD5821
5
7
VDD
10µF
Figure 26. Typical Application Circuit
Rev. 0 | Page 14 of 16
+
VCC
0.1µF
10µF
+
05950-028
XSHUTDOWN
05950-029
The AD5821 is designed to drive both spring-preloaded and
nonspring linear motors used in applications such as lens autofocus, 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 displacement or stroke, which is the actual distance the lens moves in
millimeters (mm) and the current through the motor, measured
in milliamps (mA).
AD5821
OUTLINE DIMENSIONS
0.65
0.59
0.53
1.575
1.515
1.455
SEATING
PLANE
BALL 1
IDENTIFIER
3
2
A
0.36
0.32
0.28
1.750
1.690
1.630
B
C
0.50 BSC
BALL PITCH
0.28
0.24
0.20
BOTTOM VIEW
(BALL SIDE UP)
110405-0
TOP VIEW
(BALL SIDE DOWN)
1
Figure 27. 9-Ball Wafer Level Chip Scale Package [WLCSP]
(CB-9-1)
Dimensions shown in millimeters
ORDERING GUIDE
Model
AD5821BCBZ-REEL7 1
AD5821BCBZ-REEL1
AD5821-WAFER
AD5821D-WAFER
EVAL-AD5821EBZ1
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
Package Description
9-Ball Wafer Level Chip Scale Package (WLCSP)
9-Ball Wafer Level Chip Scale Package (WLCSP)
Bare Die Wafer
Bare Die Wafer on Film
Evaluation Board
Z = Pb-free part.
Rev. 0 | Page 15 of 16
Package Option
CB-9-1
CB-9-1
Branding
D82
D82
AD5821
NOTES
Purchase of licensed I2C components of Analog Devices or one of its sublicensed Associated Companies conveys a license for the purchaser under the Philips I2C Patent
Rights to use these components in an I2C system, provided that the system conforms to the I2C Standard Specification as defined by Philips.
©2007 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D05950-0-1/07(0)
T
T
Rev. 0 | Page 16 of 16
Download PDF