EVAL-AD5680EB [ADI]
5 V 18-Bit nanoDAC in a SOT-23; 5 V 18位属于nanoDAC采用SOT- 23
| 型号： | EVAL-AD5680EB |
| 厂家： | 
ADI |
| 描述： | 5 V 18-Bit nanoDAC in a SOT-23 |
| 文件： | 总20页 (文件大小：466K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
5 V 18-Bit nanoDACTM
in a SOT-23
AD5680
FUNCTIONAL BLOCK DIAGRAM
FEATURES
V
V
DD
Single 18-bit nanoDAC
GND
REF
18-bit monotonic
V
FB
POWER-ON
RESET
12-bit accuracy guaranteed
Tiny 8-lead SOT-23 package
Power-on reset to zero scale/midscale
4.5 V to 5.5 V power supply
Serial interface
OUTPUT
BUFFER
V
OUT
REF(+)
DAC
REGISTER
18-BIT
DAC
Rail-to-rail operation
SYNC interrupt facility
Temperature range −40°C to +105°C
INPUT
CONTROL
LOGIC
APPLICATIONS
AD5680
Closed-loop process control
SYNC SCLK DIN
Low bandwidth data acquisition systems
Portable battery-powered instruments
Gain and offset adjustment
Figure 1.
Precision setpoint control
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
The AD5680, a member of the nanoDAC family, is a single,
18-bit buffered voltage-out DAC that operates from a single
4.5 V to 5.5 V supply and is 18-bit monotonic.
1. 18 bits of resolution.
2. 12-bit accuracy guaranteed for 18-bit DAC.
3. Available in an 8-lead SOT-23.
The AD5680 requires an external reference voltage to set the
output range of the DAC. The part incorporates a power-on
reset circuit that ensures the DAC output powers up to 0 V
(AD5680-1) or to midscale (AD5680-2) and remains there until
a valid write takes place.
4. Low power. Typically consumes 1.6 mW at 5 V.
5. Power-on reset to zero scale or to midscale.
RELATED DEVICES
The low power consumption of this part in normal operation
makes it ideally suited to portable battery-operated equipment.
The power consumption is 1.6 mW at 5 V.
AD5662 16-bit DAC in SOT-23.
The AD5680 on-chip precision output amplifier allows rail-to-
rail output swing to be achieved. For remote sensing applications,
the output amplifier’s inverting input is available to the user.
The AD5680 uses a versatile 3-wire serial interface that operates
at clock rates up to 30 MHz, and is compatible with standard
SPI®, QSPI™, MICROWIRE™, and DSP interface standards.
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 registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
www.analog.com
©2006 Analog Devices, Inc. All rights reserved.
AD5680
TABLE OF CONTENTS
Features .............................................................................................. 1
Output Amplifier........................................................................ 11
Interpolator Architecture .......................................................... 11
Serial Interface............................................................................ 12
Input Shift Register .................................................................... 12
Applications....................................................................................... 1
Functional Block Diagram .............................................................. 1
General Description......................................................................... 1
Product Highlights ........................................................................... 1
Related Devices................................................................................. 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Timing Characteristics..................................................................... 4
Absolute Maximum Ratings............................................................ 5
ESD Caution.................................................................................. 5
Pin Configuration and Function Description .............................. 6
Typical Performance Characteristics ............................................. 7
Terminology .................................................................................... 10
Theory of Operation ...................................................................... 11
DAC Section................................................................................ 11
Resistor String............................................................................. 11
SYNC
Interrupt .......................................................................... 12
Power-On Reset.......................................................................... 12
Microprocessor Interfacing....................................................... 13
Applications..................................................................................... 14
Closed-Loop Applications ........................................................ 14
Filter ............................................................................................. 14
Choosing a Reference for the AD5680.................................... 15
Using a Reference as a Power Supply for the AD5680 .......... 16
Using the AD5680 with a Galvanically Isolated Interface .... 16
Power Supply Bypassing and Grounding................................ 16
Outline Dimensions....................................................................... 17
Ordering Guide .......................................................................... 17
REVISION HISTORY
6/06—Revision 0: Initial Version
Rev. 0 | Page 2 of 20
AD5680
SPECIFICATIONS
VDD = 4.5 V to 5.5 V; RL = 2 kΩ to GND; CL = 200 pF to GND; VREF = VDD; all specifications TMIN to TMAX, unless otherwise noted.
Table 1.
B Grade
Typ
B Version1
Parameter
STATIC PERFORMANCE2
Min
Max
Unit
Conditions/Comments
Resolution
18
Bits
Relative Accuracy
Differential Nonlinearity3
±32
±±6
±1
±2
LSB
LSB
LSB
mV
Measured in 50 Hz system bandwidth
Measured in 300 Hz system bandwidth
All 0s loaded to DAC register
Zero-Code Error
2
10
Full-Scale Error
Offset Error
Gain Error
Zero-Code Error Drift
Gain Temperature Coefficient
DC Power Supply Rejection Ratio
OUTPUT CHARACTERISTICS3
Output Voltage Range
Output Voltage Settling Time
−0.2
−1
±10
±1.5
% FSR
mV
% FSR
μV/°C
ppm
dB
All 1s loaded to DAC register
±2
±2.5
−100
Of FSR/°C
DAC code = midscale; VDD = 5 V ± 10%
0
VDD
85
V
μs
80
¼ to ¾ scale change settling to ±8 LSB
RL = 2 kΩ; 0 pF < CL < 200 pF
Slew Rate
Capacitive Load Stability
1.5
2
V/μs
nF
¼ to ¾ scale
RL = ∞
10
80
25
−80
5
0.2
0.5
30
nF
RL = 2 kΩ
Output Noise Spectral Density6
Output Noise (0.1 Hz to 10 Hz)6
Total Harmonic Distortion (THD)6
Digital-to-Analog Glitch Impulse
Digital Feedthrough
DC Output Impedance
Short-Circuit Current6
REFERENCE INPUT
nV/√Hz
μV p-p
dB
nV-s
nV-s
Ω
DAC code = midscale, 10 kHz
DAC code = midscale
VREF = 2 V ± 300 mV p-p, f = 200 Hz
1 LSB change around major carry
mA
VDD = 5 V
Reference Current
60
75
VDD
μA
V
kΩ
VREF = VDD = 5 V
Reference Input Range5
Reference Input Impedance
LOGIC INPUTS
0.75
125
Input Current
±2
0.8
μA
V
V
All digital inputs
VDD = 5 V
VDD = 5 V
VINL, Input Low Voltage
VINH, Input High Voltage
Pin Capacitance
2
3
pF
POWER REQUIREMENTS
VDD
IDD (Normal Mode)
6.5
5.5
V
All digital inputs at 0 V or VDD
DAC active and excluding load current
VIH = VDD and VIL = GND
VDD = 6.5 V to 5.5 V
325
85
650
ꢀA
%
POWER EFFICIENCY
IOUT/IDD
ILOAD = 2 mA, VDD = 5 V
1 Temperature range for B version is −60°C to +105°C, typical at +25°C.
2 DC specifications tested with the outputs unloaded, unless otherwise stated. Linearity calculated using a reduced code range of 2068 to 2±009±.
3 Guaranteed by design and characterization; not production tested.
6 Output unloaded.
5 Reference input range at ambient where maximum DNL specification is achievable.
Rev. 0 | Page 3 of 20
AD5680
TIMING CHARACTERISTICS
All input signals are specified with tr = tf = 1 ns/V (10% to 90% of VDD) and timed from a voltage level of (VIL + VIH)/2. See Figure 2.
VDD = 4.5 V to 5.5 V; all specifications TMIN to TMAX, unless otherwise noted.
Table 2.
Limit at TMIN, TMAX
Parameter
VDD = 4.5 V to 5.5 V
Unit
Conditions/Comments
SCLK cycle time
SCLK high time
SCLK low time
SYNC to SCLK falling edge setup time
Data setup time
1
t1
33
13
13
13
5
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
t2
t3
t6
t5
t±
t7
t8
t9
t10
6.5
0
Data hold time
SCLK falling edge to SYNC rising edge
Minimum SYNC high time
SYNC rising edge to SCLK fall ignore
SCLK falling edge to SYNC fall ignore
33
13
0
1 Maximum SCLK frequency is 30 MHz at VDD = 6.5 V to 5.5 V.
t10
t1
t9
SCLK
t2
t8
t3
t7
t4
SYNC
t6
t5
DB23
DIN
DB0
Figure 2. Serial Write Operation
Rev. 0 | Page 6 of 20
AD5680
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 3.
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.
Parameter
Rating
VDD to GND
−0.3 V to +7 V
VOUT to GND
VFB to GND
VREF to GND
Digital Input Voltage to GND
Operating Temperature Range
Industrial (B Version)
Storage Temperature Range
Junction Temperature (TJ max)
Power Dissipation
−0.3 V to VDD + 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
−60°C to +105°C
−±5°C to +150°C
150°C
(TJ max − TA)/θJA
SOT-23 Package (6-Layer Board)
θJA Thermal Impedance
Reflow Soldering Peak Temperature
Pb-free
119°C/W
2±0°C
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 6000 V readily accumulate on the
human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
Rev. 0 | Page 5 of 20
AD5680
PIN CONFIGURATION AND FUNCTION DESCRIPTION
V
1
2
3
4
8
7
6
5
GND
DIN
DD
AD5680
V
REF
TOP VIEW
V
SCLK
SYNC
FB
(Not to Scale)
V
OUT
Figure 3. Pin Configuration
Table 4. Pin Function Descriptions
Pin No. Mnemonic Function
1
2
3
6
5
VDD
VREF
VFB
VOUT
SYNC
Power Supply Input. The part can be operated from 6.5 V to 5.5 V. VDD should be decoupled to GND.
Reference Voltage Input.
Feedback Connection for the Output Amplifier. VFB should be connected to VOUT for normal operation.
Analog Output Voltage from DAC. The output amplifier has rail-to-rail operation.
Level-Triggered Control Input (Active Low). This is the frame synchronization signal for the input data. When SYNC
goes low, it enables the input shift register and data is transferred in on the falling edges of the following clocks.
The DAC is updated following the 26th clock cycle unless SYNC is taken high before this edge, in which case the
rising edge of SYNC acts as an interrupt and the write sequence is ignored by the DAC.
±
7
8
SCLK
DIN
Serial Clock Input. Data is clocked into the input shift register on the falling edge of the serial clock input. Data can
be transferred at rates up to 30 MHz.
Serial Data Input. This device has a 26-bit shift register. Data is clocked into the register on the falling edge of the
serial clock input.
GND
Ground Reference Point (for all circuitry on the part).
Rev. 0 | Page ± of 20
AD5680
TYPICAL PERFORMANCE CHARACTERISTICS
40
0
–0.02
–0.04
–0.06
–0.08
V
T
= V = 5V
REF
DD
= 25°C
V
= 5V
DD
32
A
24
16
8
GAIN ERROR
0
–8
–0.01
–0.12
–16
–0.14
–0.16
FULL-SCALE ERROR
–24
–32
–40
–0.18
–0.20
0
40k
80k
120k
CODE
160k
200k
240k
–40
–20
0
20
40
60
80
100
TEMPERATURE (°C)
Figure 4. Typical INL Plot
Figure 7. Gain Error and Full-Scale Error vs. Temperature
1.0
1.5
V
= V = 5V
REF
DD
= 25°C
T
A
0.8
0.6
0.4
0.2
1.0
ZERO-SCALE ERROR
0.5
0
0
–0.5
–1.0
–1.5
–2.0
–2.5
–0.2
–0.4
–0.6
OFFSET ERROR
–0.8
–1.0
0
25k 50k 75k 100k 125k 150k 175k 200k 225k 250k
CODE
–40
–20
0
20
40
60
80
100
TEMPERATURE (°C)
Figure 5. Typical DNL Plot in 50 Hz System Bandwidth
Figure 8. Zero-Scale Error and Offset Error vs. Temperature
0.20
±4
V
= 4.5V TO 5.5V
DAC LOADED WITH
ZERO SCALE –
SINKING CURRENT
V
T
= V
REF
= 5V, 3V
DD
T = –40°C TO +105°C
DD
= 25°C
0.15
0.10
0.05
0
A
±2
±1
–0.05
–0.10
–0.15
DAC LOADED WITH
FULL SCALE –
SOURCING CURRENT
–0.20
–0.25
0
–5
–4
–3
–2
–1
0
1
2
3
4
5
300
>300
0
50
I (mA)
SYSTEM BANDWIDTH (Hz)
Figure 6. DNL Performance vs. System Bandwidth
Figure 9. Headroom at Rails vs. Source and Sink Current
Rev. 0 | Page 7 of 20
AD5680
450
400
350
300
250
200
150
100
50
V
T
= V = 5V
REF
DD
= 25°C
SCLK
A
1
2
D
IN
Δ: 1.52V
Δ: 64.8µs
@: 1.20V
V
OUT
3
0
CH1 2.00V CH2 2.00V
CH3 1.00V
M 20.0µs
CH4
1.30V
0
4000
8000
12000
CODE
16000
20000
24000
Figure 10. Supply Current vs. Code
Figure 13. Full-Scale Settling Time, 5 V
350
300
250
200
150
100
50
V
= V = 5V
REF
DD
V
DD
1
V
REF
V
OUT
2
C3 MAX
284mV
V
OUT
C3 MIN
–52mV
V
OUT
3
0
–40
CH1 3.00V CH2 3.00V
CH3 100mV
M 100µs
CH1
2.40V
–20
0
20
40
60
80
100
TEMPERATURE (°C)
Figure 14. Power-On Reset to 0 V
Figure 11. Supply Current vs. Temperature
700
T
= 25°C
A
600
500
400
300
200
100
0
V
= 5V
V
DD
DD
1
2
V
REF
V
OUT
C3 MAX
2.5V
V
OUT
C3 MIN
–40mV
V
OUT
3
CH1 3.00V CH2 3.00V
CH3 500mV
M 100µs
CH1
2.40V
0
1
2
3
4
5
V
(V)
LOGIC
Figure 12. Supply Current vs. Logic Input Voltage
Figure 15. Power-On Reset to Midscale
Rev. 0 | Page 8 of 20
AD5680
2.502500
2.502250
2.502000
2.501750
2.501500
2.501250
2.501000
2.500750
2.500500
16
14
12
10
8
V
= V = 5V
REF
DD
= 25°C
V
T
= V
DD
REF
A
T
A
= 25
°
C
13nS/SAMPLE NUMBER
1 LSB CHANGE AROUND
MIDSCALE (0x20000 TO 0x1FFFF)
GLITCH IMPULSE = 2.723nV.s
V
= 3V
DD
2.500250
2.500000
2.499750
2.499500
V
= 5V
DD
6
4
2.499250
2.499000
2.498750
0
50 100 150 200 250 300 350 400 450 500 550
SAMPLE NUMBER
0
1
2
3
4
5
6
7
8
9
10
CAPACITANCE (nF)
Figure 16. Digital-to-Analog Glitch Impulse (Negative)
Figure 19. Settling Time vs. Capacitive Load
2.5010
2.5008
2.5006
2.5004
2.5002
2.5000
2.4998
2.4996
2.4994
2.4992
2.4990
2.4988
2.4986
V
T
= V = 5V
REF
DD
= 25°C
V
T
= V = 5V
REF
= 25°C
DD
A
DAC LOADED WITH MIDSCALED
DIGITAL
FEEDTHROUGH = 0.201nV
A
DAC LOADED WITH MIDSCALE
V
REF
1
50 100 150 200 250 300 350 400 450 500
SAMPLES × 6.5ns
0
5s/DIV
Figure 20. 0.1 Hz to 10 Hz Output Noise Plot
Figure 17. Digital Feedthrough
1000
900
800
700
600
500
400
300
200
–20
–30
–40
–50
–60
–70
–80
V
= V
REF
= 5V
DD
= 25°C
V
= 5V
DD
= 25°C
T
A
T
A
MIDSCALE LOADED
FULLSCALE LOADED
= 2V ±300mV p-p
V
REF
–90
100
0
–100
100
1M
1k
10k
100k
0
1
2
3
4
5
6
7
8
9
10
FREQUENCY (Hz)
FREQUENCY (kHz)
Figure 18. Total Harmonic Distortion
Figure 21. Noise Spectral Density
Rev. 0 | Page 9 of 20
AD5680
TERMINOLOGY
Relative Accuracy or Integral Nonlinearity (INL)
Offset Error
For the DAC, relative accuracy or integral nonlinearity is a
measurement of the maximum deviation, in LSBs, from a
straight line passing through the endpoints of the DAC transfer
function. Figure 4 shows a typical INL vs. code plot.
Offset error is a measure of the difference between VOUT (actual)
and VOUT (ideal) expressed in mV in the linear region of the
transfer function. Offset error is measured on the AD5680 with
Code 2048 loaded in the DAC register. It can be negative or
positive.
Differential Nonlinearity (DNL)
DC Power Supply Rejection Ratio (PSRR)
This indicates how the output of the DAC is affected by
changes in the supply voltage. PSRR is the ratio of the change in
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. Figure 5 shows a typical DNL vs. code plot.
VOUT to a change in VDD for full-scale output of the DAC. It is
measured in dB. VREF is held at 2 V, and VDD is varied by 10%.
Zero-Code Error
Output Voltage Settling Time
Zero-code error is a measurement of the output error when
zero code (0x00000) is loaded to the DAC register. Ideally, the
output should be 0 V. The zero-code error is always positive in
the AD5680 because the output of the DAC cannot go below
0 V. It is due to a combination of the offset errors in the DAC
and the output amplifier. Zero-code error is expressed in mV. A
plot of zero-code error vs. temperature can be seen in Figure 7.
This is the amount of time it takes for the output of a DAC to
settle to a specified level for a ¼ to ¾ full-scale input change
and is measured from the 24th falling edge of SCLK.
Digital-to-Analog Glitch Impulse
Digital-to-analog glitch impulse is 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 nV-s, and is
measured when the digital input code is changed by 1 LSB at
the major carry transition (0x1FFFF to 0x20000). See Figure 16.
Full-Scale Error
Full-scale error is a measurement of the output error when full-
scale code (0x3FFFF) is loaded to the DAC register. Ideally, the
output should be VDD − 1 LSB. Full-scale error is expressed in
percent of full-scale range.
Digital Feedthrough
Digital feedthrough is a measure of the impulse injected into
the analog output of the DAC from the digital inputs of the
DAC, but is measured when the DAC output is not updated. It
is specified in nV-s and measured with a full-scale code change
on the data bus, that is, from all 0s to all 1s and vice versa.
Gain Error
This is a measure of the span error of the DAC. It is the deviation
in slope of the DAC transfer characteristic from ideal expressed
as a percent of the full-scale range.
Total Harmonic Distortion (THD)
Zero-Code Error Drift
This is the difference between an ideal sine wave and its
attenuated version using the DAC. The sine wave is used as the
reference for the DAC. The THD is a measurement of the
harmonics present on the DAC output. It is measured in dB.
This is a measurement of the change in zero-code error with a
change in temperature. It is expressed in μV/°C.
Gain Temperature Coefficient
This is a measurement of the change in gain error with changes
in temperature. It is expressed in (ppm of full-scale range)/°C.
Noise Spectral Density
This is a measurement of the internally generated random
noise. Random noise is characterized as a spectral density
(voltage per √Hz). It is measured by loading the DAC to
midscale and measuring noise at the output. It is measured in
nV/√Hz. Figure 21 shows a plot of noise spectral density.
Rev. 0 | Page 10 of 20
AD5680
THEORY OF OPERATION
DAC SECTION
OUTPUT AMPLIFIER
The AD5680 DAC is fabricated on a CMOS process. The
architecture consists of a string DAC followed by an output
buffer amplifier. Figure 22 shows a block diagram of the DAC
architecture.
The output buffer amplifier can generate rail-to-rail voltages on
its output, which gives an output range of 0 V to VDD. This output
buffer amplifier has a gain of 2 derived from a 50 kΩ resistor
divider network in the feedback path. The output amplifier’s
inverting input is available to the user, allowing for remote
sensing. This VFB pin must be connected to VOUT for normal
operation. It can drive a load of 2 kΩ in parallel with 1000 pF to
GND. The source and sink capabilities of the output amplifier can
be seen in Figure 9. The slew rate is 1.5 V/μs with a ¼ to ¾ full-
scale settling time of 10 μs.
V
DD
R
V
FB
R
REF (+)
RESISTOR
STRING
V
DAC REGISTER
OUT
REF (–)
OUTPUT
AMPLIFIER
GND
INTERPOLATOR ARCHITECTURE
Figure 22. DAC Architecture
The AD5680 contains a 16-bit DAC with an internal clock
generator and interpolator. The voltage levels generated by the
16-bit, 1 LSB step can be subdivided using the interpolator to
increase the resolution to 18 bits.
Because the input coding to the DAC is straight binary, the ideal
output voltage is given by
D
The 18-bit input code can be divided into two segments:
16-bit DAC code (DB19 to DB4) and 2-bit interpolator code
(DB3 and DB2). The input to the DAC is switched between a
16-bit code (for example, Code 1023) and a 16-bit code + 1 LSB
(for example, Code 1024). The 2-bit interpolator code deter-
mines the duty cycle of the switching and hence the 18-bit
code level. See Table 5 for an example.
⎛
⎜
⎝
⎞
⎟
⎠
VOUT = VREF
×
262144
where D is the decimal equivalent of the binary code that is
loaded to the DAC register. It can range from 0 to 262143.
RESISTOR STRING
The resistor string section is shown in Figure 23. It is simply a
string of resistors, each of value R. The code loaded to the DAC
register determines at which node on the string the voltage is
tapped off to be fed into the output amplifier. The voltage is
tapped off by closing one of the switches connecting the string
to the amplifier. Because it is a string of resistors, it is guaranteed
monotonic.
Table 5.
16-Bit
DAC Code
2-Bit
Interpolator Code
18-Bit Code
DB19 to DB2
6092
6093
6096
DB19 to DB4 DB3
DB2
Duty Cycle
1023
1023
1023
1023
1026
0
0
1
1
0
0
1
0
1
0
0
25%
50%
75%
0
6095
609±
R
R
The DAC output voltage is given by the average value of
the waveform switching between 16-bit code (C) and 16-bit
code + 1 (C + 1). The output voltage is a function of the duty
cycle of the switching.
TO OUTPUT
R
AMPLIFIER
FILTER
PLANT
18-BIT INPUT CODE
C
DAC
MUX
V
18
16
OUT
C + 1
+1
16
C + 1
C
C + 1
C
C + 1
C
75% DUTY CYCLE
50% DUTY CYCLE
R
R
INTERPOLATOR
2
25% DUTY CYCLE
CLK
Figure 24. Interpolation Architecture
Figure 23. Resistor String
Rev. 0 | Page 11 of 20
AD5680
SERIAL INTERFACE
INPUT SHIFT REGISTER
The AD5680 has a 3-wire serial interface (
, SCLK, and
The input shift register is 24 bits wide (see Figure 25). The first
four bits are don’t care bits. The next 18 bits are the data bits
followed by two don’t care bits. These are transferred to the
DAC register on the 24th falling edge of SCLK.
SYNC
DIN) that is compatible with SPI, QSPI, and MICROWIRE
interface standards as well as with most DSPs. See Figure 2 for
a timing diagram of a typical write sequence.
SYNC INTERRUPT
The write sequence begins by bringing the
line low. Data
SYNC
from the DIN line is clocked into the 24-bit shift register on the
falling edge of SCLK. The serial clock frequency can be as high
as 30 MHz, making the AD5680 compatible with high speed
DSPs. On the 24th falling clock edge, the last data bit is clocked
in and the programmed function is executed, that is, a change
In a normal write sequence, the
line is kept low for at
SYNC
least 24 falling edges of SCLK, and the DAC is updated on the
24th falling edge. However, if
is brought high before the
SYNC
24th falling edge, this acts as an interrupt to the write sequence.
The shift register is reset and the write sequence is seen as
invalid. Neither an update of the DAC register contents nor a
change in the operating mode occurs (see Figure 26).
in DAC register contents occurs. At this stage, the
line
SYNC
can be kept low or be brought high. In either case, it must be
brought high for a minimum of 33 ns before the next write
POWER-ON RESET
sequence so that a falling edge of
can initiate the next
SYNC
write sequence. Because the
when VIN = 2 V than it does when VIN = 0.8 V,
idled low between write sequences for even lower power
operation. As mentioned previously it must, however, be
brought high again just before the next write sequence.
buffer draws more current
SYNC
The AD5680 family contains a power-on reset circuit that
controls the output voltage during power-up. The AD5680-1
DAC output powers up to 0 V, and the AD5680-2 DAC output
powers up to midscale. The output remains there until a valid
write sequence is made to the DAC. This is useful in
should be
SYNC
applications where it is important to know the output state of
the DAC while it is in the process of powering up.
DB23 (MSB)
DB0 (LSB)
X
X
X
X
D17
D16
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
X
X
DATA BITS
Figure 25. Input Register Contents
SCLK
SYNC
DIN
DB23
DB0
DB23
DB0
INVALID WRITE SEQUENCE:
SYNC HIGH BEFORE 24TH FALLING EDGE
VALID WRITE SEQUENCE, OUTPUT UPDATES
ON THE 24TH FALLING EDGE
SYNC
Figure 26.
Interrupt Facility
Rev. 0 | Page 12 of 20
AD5680
MICROPROCESSOR INTERFACING
AD5680 to Blackfin® ADSP-BF53x Interface
AD5680 to 80C51/80L51 Interface
Figure 27 shows a serial interface between the AD5680 and
the Blackfin ADSP-BF53x microprocessor. The ADSP-BF53x
processor family incorporates two dual-channel synchronous
serial ports, SPORT1 and SPORT0, for serial and multiprocessor
communications. Using SPORT0 to connect to the AD5680, the
setup for the interface is as follows. DT0PRI drives the DIN pin
of the AD5680, while TSCLK0 drives the SCLK of the part. The
Figure 29 shows a serial interface between the AD5680 and the
80C51/80L51 microcontroller. The setup for the interface is as
follows. TxD of the 80C51/80L51 drives SCLK of the AD5680,
while RxD drives the serial data line of the part. The
SYNC
signal is again derived from a bit-programmable pin on the port.
In this case, port line P3.3 is used. When data is to be transmitted
to the AD5680, P3.3 is taken low. The 80C51/80L51 transmits
data in 8-bit bytes only; thus only eight falling clock edges occur
in the transmit cycle. To load data to the DAC, P3.3 is left low
after the first eight bits are transmitted, and a second write cycle
is initiated to transmit the second byte of data. P3.3 is taken
high following the completion of this cycle. The 80C51/80L51
outputs the serial data in a format that has the LSB first. The
AD5680 must receive data with the MSB first. The 80C51/80L51
transmit routine should take this into account.
is driven from TFS0.
SYNC
ADSP-BF53x*
AD5680*
TFS0
DTOPRI
TSCLK0
SYNC
DIN
SCLK
*ADDITIONAL PINS OMITTED FOR CLARITY
AD5680*
80C51/80L51*
Figure 27. AD5680 to Blackfin ADSP-BF53x Interface
P3.3
TxD
RxD
SYNC
SCLK
DIN
AD5680 to 68HC11/68L11 Interface
Figure 28 shows a serial interface between the AD5680 and the
68HC11/68L11 microcontroller. SCK of the 68HC11/68L11
drives the SCLK of the AD5680, while the MOSI output drives
the serial data line of the DAC.
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 29. AD5680 to 80C51/80L51 Interface
The
signal is derived from a port line (PC7). The setup
SYNC
AD5680 to MICROWIRE Interface
conditions for correct operation of this interface are as follows.
The 68HC11/68L11 is configured with its CPOL bit as 0 and its
CPHA bit as 1. When data is being transmitted to the DAC, the
Figure 30 shows an interface between the AD5680 and any
MICROWIRE-compatible device. Serial data is shifted out on
the falling edge of the serial clock and is clocked into the AD5680
on the rising edge of the SK.
line is taken low (PC7). When the 68HC11/68L11 is
SYNC
configured this way, data appearing on the MOSI output is valid
on the falling edge of SCK. Serial data from the 68HC11/68L11
is transmitted in 8-bit bytes with only eight falling clock edges
occurring in the transmit cycle. Data is transmitted MSB first. To
load data to the AD5680, PC7 is left low after the first eight bits
are transferred, and a second serial write operation is performed
to the DAC; PC7 is taken high at the end of this procedure.
AD5680*
MICROWIRE*
CS
SK
SO
SYNC
SCLK
DIN
*ADDITIONAL PINS OMITTED FOR CLARITY
68HC11/68L11*
AD5680*
Figure 30. AD5680 to MICROWIRE Interface
PC7
SCK
SYNC
SCLK
DIN
MOSI
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 28. AD5680 to 68HC11/68L11 Interface
Rev. 0 | Page 13 of 20
AD5680
APPLICATIONS
CLOSED-LOOP APPLICATIONS
The AD5680 is suitable for closed-loop low bandwidth
applications. Ideally, the system bandwidth acts as a filter on the
DAC output. (See the Filter section for details of the DAC
output prefiltering and postfiltering.) The DAC updates at the
interpolation frequency of 10 kHz.
Δ: 2.09ms
@: 1.28ms
2
PLANT
CONTROLLER
DAC
CODE 4092
CODE 4094
1
ADC
M 500µs
CH2
1.4V
CH1 20.0µV CH2 5V
Figure 33. DAC Output with 50 Hz Filter on Output
Figure 31. Typical Closed-Loop Application
Δ: 2.09ms
@: 1.28ms
FILTER
2
The DAC output voltage for code transition 4092 to 4094 can be
seen in Figure 32. This is the DAC output unfiltered. Code 4092
does not have any interpolation but code 4094 has interpolation
with a 50% duty cycle. See Table 5. Figure 33 shows the DAC
output with a 50 Hz passive RC filter and Figure 34 shows the
output with a 300 Hz passive RC filter. An RC combination of
320 kΩ and 10 nF has been used to achieve the 50 Hz cutoff
frequency, and an RC combination of 81 kΩ and 10 nF has
been used to achieve the 300 Hz cutoff frequency.
1
CODE 4092
CODE 4094
M 500µs
CH2
1.4V
CH1 20.0µV CH2 5V
Figure 34. DAC Output with 300 Hz Filter on Output
CODE 4092
CODE 4094
1
M 500µs
CH4
0V
CH1 20.0µV
Figure 32. DAC Output Unfiltered
Rev. 0 | Page 16 of 20
AD5680
CHOOSING A REFERENCE FOR THE AD5680
To achieve the optimum performance from the AD5680,
choose a precision voltage reference carefully. The AD5680 has
only one reference input, VREF. The voltage on the reference
input is used to supply the positive input to the DAC. Therefore
any error in the reference is reflected in the DAC.
Long-term drift is a measurement of how much the reference
drifts over time. A reference with a tight long-term drift
specification ensures that the overall solution remains relatively
stable during its entire lifetime.
The temperature coefficient of a reference’s output voltage
affects INL, DNL, and TUE. A reference with a tight temperature
coefficient specification should be chosen to reduce temperature
dependence of the DAC output voltage in ambient conditions.
When choosing a voltage reference for high accuracy applica-
tions, the sources of error are initial accuracy, ppm drift, long-
term drift, and output voltage noise. Initial accuracy on the
output voltage of the DAC leads to a full-scale error in the
DAC. To minimize these errors, a reference with high initial
accuracy is preferred. Also, choosing a reference with an output
trim adjustment, such as the ADR425, allows a system designer
to trim out system errors by setting a reference voltage to a
voltage other than the nominal. The trim adjustment can also
be used at temperature to trim out any error.
In high accuracy applications, which have a relatively low noise
budget, reference output voltage noise needs to be considered. It
is important to choose a reference with as low an output noise
voltage as practical for the system noise resolution required.
Precision voltage references such as the ADR425 produce low
output noise in the 0.1 Hz to 10 Hz range. Examples of recom-
mended precision references for use as supply to the AD5680
are shown in the Table 6.
Table 6. Partial List of Precision References for Use with the AD5680
Part No.
ADR625
ADR395
REF195
Initial Accuracy (mV max)
Temp. Drift (ppmoC max)
0.1 Hz to 10 Hz Noise (μV p-p typ)
VOUT (V)
±2
±±
±2
3
25
5
3.6
5
50
5
5
5
Rev. 0 | Page 15 of 20
AD5680
5V
USING A REFERENCE AS A POWER SUPPLY FOR
THE AD5680
REGULATOR
10µF
0.1µF
POWER
Because the supply current required by the AD5680 is extremely
low, an alternative option is to use a voltage reference to supply
the required voltage to the part (see Figure 35). This is especially
useful if the power supply is quite noisy, or if the system supply
voltages are at some value other than 5 V, for example, 15 V.
The voltage reference outputs a steady supply voltage for the
AD5680; see Table 6 for a suitable reference. If the low dropout
REF195 is used, it must supply 325 μA of current to the
AD5680, with no load on the output of the DAC. When the
DAC output is loaded, the REF195 also needs to supply the
current to the load. The total current required (with a 5 kΩ
load on the DAC output) is
V
DD
VOA
SCLK
V1A
V1B
SCLK
SYNC
ADuM1300
AD5680
V
OUT
SDI
VOB
VOC
V1C
DIN
DATA
GND
325 μA + (5 V/5 kΩ) = 1.33 mA
Figure 36. AD5680 with a Galvanically Isolated Interface
The load regulation of the REF195 is typically 2 ppm/mA,
which results in a 2.7 ppm (13.5 μV) error for the 1.33 mA
current drawn from it. This corresponds to a 0.177 LSB error.
POWER SUPPLY BYPASSING AND GROUNDING
When accuracy is important in a circuit, it is helpful to carefully
consider the power supply and ground return layout on the
board. The printed circuit board containing the AD5680 should
have separate analog and digital sections, each having its own
area of the board. If the AD5680 is in a system where other
devices require an AGND-to-DGND connection, the connection
should be made at one point only. This ground point should be
as close as possible to the AD5680.
15V
5V
REF195
250µA
V
V
REF
DD
SYNC
SCLK
DIN
3-WIRE
SERIAL
INTERFACE
V
= 0V TO 5V
OUT
AD5680
The power supply to the AD5680 should be bypassed with 10 μF
and 0.1 μF capacitors. The capacitors should be located as close
as possible to the device, with the 0.1 μF capacitor ideally right
up against the device. The 10 μF capacitors are the tantalum
bead type. It is important that the 0.1 μF capacitor has low
effective series resistance (ESR) and effective series inductance
(ESI), for example, common ceramic types of capacitors. This
0.1 μF capacitor provides a low impedance path to ground for
high frequencies caused by transient currents due to internal
logic switching.
Figure 35. REF195 as Power Supply to the AD5680
USING THE AD5680 WITH A GALVANICALLY
ISOLATED INTERFACE
In process-control applications in industrial environments, it is
often necessary to use a galvanically isolated interface to protect
and isolate the controlling circuitry from any hazardous
common-mode voltages that might occur in the area where the
DAC is functioning. Isocouplers provide isolation in excess of
3 kV. The AD5680 uses a 3-wire serial logic interface, so the
ADuM130x 3-channel digital isolator provides the required
isolation (see Figure 36). The power supply to the part also
needs to be isolated, which is done by using a transformer. On
the DAC side of the transformer, a 5 V regulator provides the
5 V supply required for the AD5680.
The power supply line itself should have as large a trace as
possible to provide a low impedance path and to 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,
ensure that they run at right angles to each other to reduce
feedthrough effects on the board. The best board layout
technique is the microstrip technique 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 1± of 20
AD5680
OUTLINE DIMENSIONS
2.90 BSC
8
1
7
2
6
3
5
4
1.60 BSC
2.80 BSC
PIN 1
INDICATOR
0.65 BSC
1.95
BSC
1.30
1.15
0.90
1.45 MAX
0.22
0.08
0.60
0.45
0.30
8°
4°
0°
0.38
0.22
0.15 MAX
SEATING
PLANE
COMPLIANT TO JEDEC STANDARDS MO-178-BA
Figure 37. 8-Lead Small Outline Transistor Package [SOT-23]
(RJ-8)
Dimensions shown in millimeters
ORDERING GUIDE
Package
Description
Package
Option
Power-On
Reset to Code
Model
Temperature Range
Branding
D3C
D3C
D3D
D3D
Accuracy
AD5±80BRJZ-1500RL71
AD5±80BRJZ-1REEL71
AD5±80BRJZ-2500RL71
AD5±80BRJZ-2REEL71
EVAL-AD5±80EB
−60°C to +105°C
−60°C to +105°C
−60°C to +105°C
−60°C to +105°C
8-lead SOT-23
8-lead SOT-23
8-lead SOT-23
8-lead SOT-23
Evaluation Board
RJ-8
RJ-8
RJ-8
RJ-8
Zero
Zero
Midscale
Midscale
±±6 LSB INL
±±6 LSB INL
±±6 LSB INL
±±6 LSB INL
1 Z = Pb-free part.
Rev. 0 | Page 17 of 20
AD5680
NOTES
Rev. 0 | Page 18 of 20
AD5680
NOTES
Rev. 0 | Page 19 of 20
AD5680
NOTES
©2006 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D05854–0–6/06(0)
Rev. 0 | Page 20 of 20
相关型号：
EVAL-AD5755-1SDZ
Quad Channel, 16-Bit,Serial Input, 4 mA to 20 mA and Voltage Output DAC,Dynamic Power Control
ADI
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