4 × 12-Bit and 4 × 16-Bit Octal DAC with
On-Chip Reference in 14-Lead TSSOP
AD5678
Low power octal DAC with
Four 16-bit DACs
Four 12-bit DACs
14-lead/16-lead TSSOP
On-chip 1.25 V/2.5 V, 5 ppm/°C reference
Power down to 400 nA @ 5 V, 200 nA @ 3 V
2.7 V to 5.5 V power supply
Guaranteed monotonic by design
Power-on reset to zero scale
3 power-down functions
Hardware LDAC and LDAC override function
CLR function to programmable code
Rail-to-rail operation
FUNCTIONAL BLOCK DIAGRAM
VREFIN/VREFOUT
VDD
AD5678
1.25V/2.5V
REF
LDAC
INPUT
REGISTER
INPUT
REGISTER
INPUT
REGISTER
SCLK
SYNC
INTERFACE
LOGIC
INPUT
REGISTER
INPUT
REGISTER
DIN
DAC
REGISTER
DAC
REGISTER
DAC
REGISTER
DAC
REGISTER
DAC
REGISTER
STRING
DAC B
STRING
DAC C
STRING
DAC D
STRING
DAC E
INPUT
REGISTER
DAC
REGISTER
STRING
DAC F
INPUT
REGISTER
DAC
REGISTER
STRING
DAC G
INPUT
REGISTER
DAC
REGISTER
STRING
DAC H
BUFFER
VOUTA
BUFFER
VOUTB
BUFFER
VOUTC
BUFFER
VOUTD
BUFFER
VOUTE
BUFFER
VOUTF
BUFFER
VOUTG
BUFFER
VOUTH
POWER-DOWN
LOGIC
POWER-ON
RESET
GND
LDAC1 CLR1
APPLICATIONS
STRING
DAC A
1RU-16 PACKAGE ONLY
05299-001
FEATURES
Figure 1.
Process control
Data acquisition systems
Portable battery-powered instruments
Digital gain and offset adjustment
Programmable voltage current sources
Programmable attenuators
GENERAL DESCRIPTION
The AD5678 is a low power, octal, buffered voltage-output
DAC with four 12-bit DACs and four 16-bit DACs in a single
package. All devices operate from a single 2.7 V to 5.5 V supply
and are guaranteed monotonic by design.
The AD5678 has an on-chip reference with an internal gain of 2.
The AD5678-1 has a 1.25 V 5 ppm/°C reference, giving a fullscale output of 2.5 V; the AD5678-2 has a 2.5 V 5 ppm/°C
reference, giving a full-scale output of 5 V. The on-board
reference is off at power-up, allowing the use of an external
reference. The internal reference is enabled via a software write.
The part incorporates a power-on reset circuit that ensures that
the DAC output powers up to 0 V and remains powered up at
this level until a valid write takes place. The part contains a
power-down feature that reduces the current consumption of
the device to 400 nA at 5 V and provides software-selectable
output loads while in power-down mode for any or all DAC
channels.
The outputs of all DACs can be updated simultaneously using
the LDAC function, with the added functionality of userselectable DAC channels to simultaneously update. There is
also an asynchronous CLR that clears all DACs to a softwareselectable code—0 V, midscale, or full scale.
The AD5678 utilizes a versatile 3-wire serial interface that
operates at clock rates of up to 50 MHz and is compatible with
standard SPI®, QSPI™, MICROWIRE™, and DSP interface
standards. The on-chip precision output amplifier enables railto-rail output swing.
PRODUCT HIGHLIGHTS
1.
2.
3.
4.
5.
Octal DAC (four 12-bit DACs and four 16-bit DACs).
On-chip 1.25 V/2.5 V, 5 ppm/°C reference.
Available in 14-lead/16-lead TSSOP.
Power-on reset to 0 V.
Power-down capability. When powered down, the DAC
typically consumes 200 nA at 3 V and 400 nA at 5 V.
Rev. C
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 ©2005–2011 Analog Devices, Inc. All rights reserved.
AD5678
TABLE OF CONTENTS
Features .............................................................................................. 1
D/A Section................................................................................. 20
Applications....................................................................................... 1
Resistor String............................................................................. 20
Functional Block Diagram .............................................................. 1
Internal Reference ...................................................................... 20
General Description ......................................................................... 1
Output Amplifier........................................................................ 21
Product Highlights ........................................................................... 1
Serial Interface ............................................................................ 21
Revision History ............................................................................... 2
Input Shift Register .................................................................... 22
Specifications..................................................................................... 3
SYNC Interrupt .......................................................................... 22
AC Characteristics........................................................................ 7
Internal Reference Register....................................................... 23
Timing Characteristics ................................................................ 8
Power-On Reset.......................................................................... 23
Absolute Maximum Ratings............................................................ 9
Power-Down Modes .................................................................. 23
ESD Caution.................................................................................. 9
Clear Code Register ................................................................... 23
Pin Configuration and Function Descriptions........................... 10
LDAC Function .......................................................................... 25
Typical Performance Characteristics ........................................... 11
Power Supply Bypassing and Grounding................................ 25
Terminology .................................................................................... 18
Outline Dimensions ....................................................................... 26
Theory of Operation ...................................................................... 20
Ordering Guide .......................................................................... 26
REVISION HISTORY
2/11—Rev. B to Rev. C
Changes to Zero-Code Error Parameter and Offset Error
Parameter, Table 1............................................................................. 3
Changes to Zero-Code Error Parameter and Offset Error
Parameter, Table 2............................................................................. 5
2/09—Rev. A to Rev. B
Changes to Reference Current Parameter, Table 1....................... 3
Change to IDD (Normal Mode) Parameter, Table 1 ...................... 4
Changes to Reference Current Parameter, Table 2....................... 5
Change to IDD (Normal Mode) Parameter, Table 2 ...................... 6
11/05—Rev. 0 to Rev. A
Change to General Description ...................................................... 1
Change to Specifications.................................................................. 3
Replaced Figure 48 ......................................................................... 22
Change to the Power-Down Modes Section ............................... 23
10/05—Revision 0: Initial Version
Rev. C | Page 2 of 28
AD5678
SPECIFICATIONS
VDD = 4.5 V to 5.5 V, RL = 2 kΩ to GND, CL = 200 pF to GND, VREFIN = VDD. All specifications TMIN to TMAX, unless otherwise noted.
Table 1.
Parameter
STATIC PERFORMANCE 2
AD5678 (DAC C, D, E, F)
Resolution
Relative Accuracy
Differential Nonlinearity
AD5678 (DAC A, B, G, H)
Resolution
Relative Accuracy
Differential Nonlinearity
Zero-Code Error
Zero-Code Error Drift
Full-Scale Error
Gain Error
Gain Temperature
Coefficient
Offset Error
DC Power Supply Rejection
Ratio
DC Crosstalk
(External Reference)
A Grade 1
Min
Typ Max
B Grade1
Min
Typ Max
12
12
DC Output Impedance
Short-Circuit Current
Power-Up Time
REFERENCE INPUTS
Reference Input Voltage
Reference Current
Reference Input Range
Reference Input Impedance
REFERENCE OUTPUT
Output Voltage
AD5678-2
Reference TC3
Reference Output Impedance
LOGIC INPUTS3
Input Current
Input Low Voltage, VINL
Input High Voltage, VINH
Pin Capacitance
±2
±0.25
±8
±32
±1
19
16
±0.5
±1
±0.25
±8
±16
±1
19
16
6
±2
−0.2
6
±2
−0.2
−1
±1
±2.5
±6
–80
DC Crosstalk
(Internal Reference)
OUTPUT CHARACTERISTICS 3
Output Voltage Range
Capacitive Load Stability
±0.5
−1
±1
±2.5
±19
±6
–80
±19
Unit
Bits
LSB
LSB
Bits
LSB
LSB
mV
μV/°C
% FSR
% FSR
ppm
mV
dB
10
10
μV
5
10
25
5
10
25
μV/mA
μV
μV
10
10
μV/mA
0
VDD
0
VDD
2
10
0.5
30
4
VDD
35
0
2
10
0.5
30
4
55
VDD
VDD
35
0
14.6
2.495
±5
7.5
14.6
2.505
±10
2.495
±5
7.5
±3
0.8
2
55
VDD
V
μA
V
kΩ
See Figure 11
Guaranteed monotonic by design
(see Figure 12)
See Figure 5
Guaranteed monotonic by design (see Figure 6)
All 0s loaded to DAC register (see Figure 17)
All 1s loaded to DAC register (see Figure 18)
Of FSR/°C
VDD ± 10%
Due to full-scale output change,
RL = 2 kΩ to GND or VDD
Due to load current change
Due to powering down (per channel)
Due to full-scale output change,
RL = 2 kΩ to GND or VDD
Due to load current change
RL = ∞
RL = 2 kΩ
VDD = 5 V
Coming out of power-down mode; VDD = 5 V
±1% for specified performance
VREF = VDD = 5.5 V (per DAC channel)
Per DAC channel
2.505
±10
V
ppm/°C
kΩ
At ambient
±3
0.8
μA
V
V
pF
All digital inputs
VDD = 5 V
VDD = 5 V
2
3
V
nF
nF
Ω
mA
μs
Conditions/Comments
3
Rev. C | Page 3 of 28
AD5678
Parameter
POWER REQUIREMENTS
VDD
IDD (Normal Mode) 4
VDD = 4.5 V to 5.5 V
VDD = 4.5 V to 5.5 V
IDD (All Power-Down Modes) 5
VDD = 4.5 V to 5.5 V
A Grade 1
Min
Typ Max
B Grade1
Min
Typ Max
Unit
Conditions/Comments
4.5
4.5
5.5
V
5.5
1.3
2
1.8
2.6
1.3
2
1.8
2.6
mA
mA
All digital inputs at 0 or VDD,
DAC active, excludes load current
VIH = VDD and VIL = GND
Internal reference off
Internal reference on
0.4
1
0.4
1
μA
VIH = VDD and VIL = GND
1
Temperature range is −40°C to +105°C, typical at 25°C.
Linearity calculated using a reduced code range of AD5678 12-bit DACs (Code 32 to Code 4,064) and AD5678 16-bit DACs (Code 512 to Code 65,024). Output
unloaded.
3
Guaranteed by design and characterization; not production tested.
4
Interface inactive. All DACs active. DAC outputs unloaded.
5
All eight DACs powered down.
2
Rev. C | Page 4 of 28
AD5678
VDD = 2.7 V to 3.6 V, RL = 2 kΩ to GND, CL = 200 pF to GND, VREFIN = VDD. All specifications TMIN to TMAX, unless otherwise noted.
Table 2.
Parameter
STATIC PERFORMANCE 2
AD5678 (DAC C, D, E, F)
Resolution
Relative Accuracy
Differential Nonlinearity
AD5678 (DAC A, B, G, H)
Resolution
Relative Accuracy
Differential Nonlinearity
Zero-Code Error
Zero-Code Error Drift
Full-Scale Error
Gain Error
Gain Temperature Coefficient
Offset Error
Offset Temperature Coefficient
DC Power Supply Rejection
Ratio
DC Crosstalk
(External Reference)
A Grade 1
Min
Typ Max
B Grade1
Min
Typ Max
12
12
±0.5
16
DC Output Impedance
Short-Circuit Current
Power-Up Time
REFERENCE INPUTS
Reference Input Voltage
Reference Current
Reference Input Range
Reference Input Impedance
REFERENCE OUTPUT
Output Voltage
AD5678-1
Reference TC3
Reference Output Impedance
±0.5
±1
±1
16
6
±2
−0.2
±2.5
±6
1.7
–80
DC Crosstalk
(Internal Reference)
OUTPUT CHARACTERISTICS 3
Output Voltage Range
Capacitive Load Stability
±2
±1
±32
±1
19
6
±2
−0.2
−1
±1
±2.5
±6
1.7
–80
±19
±16
±1
19
−1
±1
±19
Unit
Bits
LSB
LSB
Bits
LSB
LSB
mV
μV/°C
% FSR
% FSR
ppm
mV
μV/°C
dB
10
10
μV
4.5
10
25
4.5
10
25
μV/mA
μV
μV
4.5
4.5
μV/mA
0
VDD
0
VDD
2
10
0.5
30
4
VDD
20
0
2
10
0.5
30
4
55
VDD
VDD
20
0
14.6
1.247
±5
7.5
55
VDD
14.6
1.253
±15
1.247
±5
7.5
1.253
±15
Rev. C | Page 5 of 28
V
nF
nF
Ω
mA
μs
V
μA
V
kΩ
V
ppm/°C
kΩ
Conditions/Comments
See Figure 11
Guaranteed monotonic by design
(see Figure 12)
See Figure 5
Guaranteed monotonic by design (See Figure 6)
All 0s loaded to DAC register (See Figure 17)
All 1s loaded to DAC register (See Figure 18)
Of FSR/°C
VDD ± 10%
Due to full-scale output change,
RL = 2 kΩ to GND or VDD
Due to load current change
Due to powering down (per channel)
Due to full-scale output change,
RL = 2 kΩ to GND or VDD
Due to load current change
RL = ∞
RL = 2 kΩ
VDD = 3 V
Coming out of power-down mode; VDD = 3 V
±1% for specified performance
VREF = VDD = 3.6 V (per DAC channel)
Per DAC channel
At ambient
AD5678
Parameter
LOGIC INPUTS3
Input Current
Input Low Voltage, VINL
Input High Voltage, VINH
Pin Capacitance
POWER REQUIREMENTS
VDD
IDD (Normal Mode) 4
VDD = 2.7 V to 3.6 V
VDD = 2.7 V to 3.6 V
IDD (All Power-Down Modes) 5
VDD = 2.7 V to 3.6 V
A Grade 1
Min
Typ Max
B Grade1
Min
Typ Max
±3
0.8
2
Unit
Conditions/Comments
±3
0.8
μA
V
V
pF
All digital inputs
VDD = 3 V
VDD = 3 V
3.6
V
2
3
2.7
3
3.6
2.7
1.2
1.7
1.7
2.6
1.2
1.7
1.7
2.6
mA
mA
All digital inputs at 0 or VDD,
DAC active, excludes load current
VIH = VDD and VIL = GND
Internal reference off
Internal reference on
0.2
1
0.2
1
μA
VIH = VDD and VIL = GND
1
Temperature range is −40°C to +105°C, typical at 25°C.
Linearity calculated using a reduced code range of AD5678 12-bit DACs (Code 32 to Code 4,064) and AD5678 16-bit DACs (Code 512 to Code 65,024). Output
unloaded.
3
Guaranteed by design and characterization; not production tested.
4
Interface inactive. All DACs active. DAC outputs unloaded.
5
All eight DACs powered down.
2
Rev. C | Page 6 of 28
AD5678
AC CHARACTERISTICS
VDD = 2.7 V to 5.5 V, RL = 2 kΩ to GND, CL = 200 pF to GND, VREFIN = VDD. All specifications TMIN to TMAX, unless otherwise noted.
Table 3.
Parameter 1, 2
Output Voltage Settling Time
Slew Rate
Digital-to-Analog Glitch Impulse
Digital Feedthrough
Reference Feedthrough
Digital Crosstalk
Analog Crosstalk
DAC-to-DAC Crosstalk
Multiplying Bandwidth
Total Harmonic Distortion
Output Noise Spectral Density
Output Noise
Min
Typ
6
1.5
4
0.1
−90
0.5
2.5
3
340
−80
120
100
15
Max
10
Unit
μs
V/μs
nV-s
nV-s
dB
nV-s
nV-s
nV-s
kHz
dB
nV/√Hz
nV/√Hz
μV p-p
Conditions/Comments 3
¼ to ¾ scale settling to ±2 LSB
1 LSB change around major carry (see Figure 34)
VREF = 2 V ± 0.1 V p-p, frequency = 10 Hz to 20 MHz
VREF = 2 V ± 0.2 V p-p
VREF = 2 V ± 0.1 V p-p, frequency = 10 kHz
DAC code = 0x8400, 1 kHz
DAC code = 0x8400, 10 kHz
0.1 Hz to 10 Hz
1
Guaranteed by design and characterization; not production tested.
See the Terminology section.
3
Temperature range is −40°C to +105°C, typical at 25°C.
2
Rev. C | Page 7 of 28
AD5678
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 = 2.7 V to 5.5 V. All specifications TMIN to TMAX, unless otherwise noted.
Table 4.
Limit at TMIN, TMAX
VDD = 2.7 V to 5.5 V
20
8
8
13
4
4
0
15
13
0
10
15
5
0
300
Parameter
t1 1
t2
t3
t4
t5
t6
t7
t8
t9
t10
t11
t12
t13
t14
t15
Conditions/Comments
SCLK cycle time
SCLK high time
SCLK low time
SYNC to SCLK falling edge set-up time
Data set-up time
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
LDAC pulse width low
SCLK falling edge to LDAC rising edge
CLR pulse width low
SCLK falling edge to LDAC falling edge
CLR pulse activation time
Maximum SCLK frequency is 50 MHz at VDD = 2.7 V to 5.5 V. Guaranteed by design and characterization; not production tested.
t10
t1
t9
SCLK
t8
t3
t4
t2
t7
SYNC
t5
DIN
t6
DB31
DB0
t14
t11
LDAC1
t12
LDAC2
CLR
VOUT
t13
t15
05299-002
1
Unit
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns typ
1ASYNCHRONOUS LDAC UPDATE MODE.
2SYNCHRONOUS LDAC UPDATE MODE.
Figure 2. Serial Write Operation
Rev. C | Page 8 of 28
AD5678
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 5.
Parameter
VDD to GND
Digital Input Voltage to GND
VREFIN/VREFOUT to GND
Operating Temperature Range
Industrial (B Version)
Storage Temperature Range
Junction Temperature (TJ MAX)
TSSOP Package
Power Dissipation
θJA Thermal Impedance
Lead Temperature, Soldering
SnPb
Pb Free
Rating
−0.3 V to +7 V
−0.3 V to VDD + 0.3 V
−0.3 V to VDD + 0.3 V
−40°C to +105°C
−65°C to +150°C
150°C
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.
(TJ MAX − TA)/θJA
150.4°C/W
240°C
260°C
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 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. C | Page 9 of 28
AD5678
LDAC 1
16
SCLK
SYNC 2
15
DIN
AD5678
14
GND
TOP VIEW
(Not to Scale)
13
VOUTB
12
VOUTD
1
14
SCLK
VDD
2
13
DIN
VDD
VOUTA
3
AD5678
12
GND
VOUTA 4
VOUTC
4
11
VOUTB
VOUTC
5
VOUTE
5
TOP VIEW
(Not to Scale)
10
VOUTD
VOUTE
6
11
VOUTF
VOUTG
6
9
VOUTF
VOUTG
7
10
VOUTH
VREFIN/VREFOUT
7
8
VOUTH
VREFIN/VREFOUT
8
9
05299-003
SYNC
Figure 3. 14-Lead TSSOP (RU-14)
3
CLR
05299-004
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
Figure 4. 16-Lead TSSOP (RU-16)
Table 6. Pin Function Descriptions
Pin No.
14-Lead
16-Lead
TSSOP
TSSOP
Mnemonic
Description
N/A
1
LDAC
1
2
SYNC
2
3
VDD
3
11
4
10
7
4
13
5
12
8
VOUTA
VOUTB
VOUTC
VOUTD
VREFIN/VREFOUT
N/A
9
CLR
5
9
6
8
12
13
6
11
7
10
14
15
VOUTE
VOUTF
VOUTG
VOUTH
GND
DIN
14
16
SCLK
Pulsing this pin low allows any or all DAC registers to be updated if the input registers have
new data. This allows all DAC outputs to simultaneously update. Alternatively, this pin can be
tied permanently low.
Active Low Control Input. This is the frame synchronization signal for the input data. When
SYNC goes low, it powers on the SCLK and DIN buffers and enables the input shift register.
Data is transferred in on the falling edges of the next 32 clocks. If SYNC is taken high before
the 32nd falling edge, the rising edge of SYNC acts as an interrupt and the write sequence is
ignored by the device.
Power Supply Input. These parts can be operated from 2.7 V to 5.5 V, and the supply should
be decoupled with a 10 μF capacitor in parallel with a 0.1 μF capacitor to GND.
Analog Output Voltage from DAC A. The output amplifier has rail-to-rail operation.
Analog Output Voltage from DAC B. The output amplifier has rail-to-rail operation.
Analog Output Voltage from DAC C. The output amplifier has rail-to-rail operation.
Analog Output Voltage from DAC D. The output amplifier has rail-to-rail operation.
The AD5678 has a common pin for reference input and reference output. When using the
internal reference, this is the reference output pin. When using an external reference, this is
the reference input pin. The default for this pin is as a reference input.
Asynchronous Clear Input. The CLR input is falling edge sensitive. When CLR is low, all LDAC
pulses are ignored. When CLR is activated, the input register and the DAC register are
updated with the data contained in the CLR code register—zero, midscale, or full scale.
Default setting clears the output to 0 V.
Analog Output Voltage from DAC E. The output amplifier has rail-to-rail operation.
Analog Output Voltage from DAC F. The output amplifier has rail-to-rail operation.
Analog Output Voltage from DAC G. The output amplifier has rail-to-rail operation.
Analog Output Voltage from DAC H. The output amplifier has rail-to-rail operation.
Ground Reference Point for All Circuitry on the Part.
Serial Data Input. This device has a 32-bit shift register. Data is clocked into the register on
the falling edge of the serial clock input.
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 of up to 50 MHz.
Rev. C | Page 10 of 28
AD5678
TYPICAL PERFORMANCE CHARACTERISTICS
1.0
10
VDD = VREF = 5V
TA = 25°C
8
0.6
DNL ERROR (LSB)
6
2
0
–2
–4
0.4
0.2
0
–0.2
–0.4
–0.8
05299-011
60000
65000
65000
55000
60000
50000
45000
40000
35000
30000
25000
20000
15000
–1.0
5k 10k 15k 20k 25k 30k 35k 40k 45k 50k 55k 60k 65k
CODE
10000
0
0
–8
05299-014
–0.6
–6
5000
INL ERROR (LSB)
4
–10
VDD = 5V
VREFOUT = 2.5V
TA = 25°C
0.8
CODE
Figure 8. DNL 16-Bit DAC, 2.5 V Internal Reference
Figure 5. INL—16-Bit DAC
10
1.0
0.8
6
INL ERROR (LSB)
0.4
0.2
0
–0.2
4
2
0
–2
–4
–0.4
05299-012
–8
55000
50000
45000
40000
0
60k
35000
50k
30000
40k
25000
30k
CODE
20000
20k
15000
10k
10000
0
–10
5000
–0.8
CODE
Figure 6. DNL—16-Bit DAC
Figure 9. INL—16-Bit DAC, 1.25 V Internal Reference
1.0
0.6
0.2
0
–6
–0.6
CODE
60000
55000
50000
45000
–1.0
40000
65000
60000
55000
50000
45000
40000
35000
30000
25000
20000
15000
10000
0
5000
–0.8
0
–8
–10
CODE
Figure 7. INL—16-Bit DAC, 2.5 V Internal Reference
Figure 10. DNL—16-Bit DAC, 1.25 V Internal Reference
Rev. C | Page 11 of 28
65000
–0.4
05299-013
–4
05299-016
–0.2
35000
0
–2
0.4
30000
2
25000
DNL ERROR (LSB)
4
VDD = 3V
VREFOUT = 1.25V
TA = 25°C
20000
6
0.8
15000
VDD = 5V
VREFOUT = 2.5V
TA = 25°C
8
10000
10
INL ERROR (LSB)
05299-015
–6
–0.6
5000
DNL ERROR (LSB)
0.6
–1.0
VDD = 3V
VREFOUT = 1.25V
TA = 25°C
8
VDD = VREF = 5V
TA = 25°C
AD5678
1.0
VDD = VREF = 5V
0.8 TA = 25°C
0.20
0.10
DNL ERROR (LSB)
0.2
0
–0.2
–0.4
–0.6
0.05
0
–0.05
05299-045
–0.10
0
500
1000
1500
2000
2500
CODE
3000
3500
–0.15
4000
–0.20
Figure 11. INL—12-Bit DAC
0.20
0.6
0.05
INL ERROR (LSB)
1500
2000 2500
CODE
3000
3500
4000
0
–0.05
0.4
0.2
0
–0.2
–0.4
–0.6
05299-046
–0.15
0
500
1000
1500
2000 2500
CODE
3000
3500
05299-049
DNL ERROR (LSB)
1000
VDD = 3V
VREFOUT = 1.25V
TA = 25°C
0.8
–0.10
–0.8
–1.0
4000
0
Figure 12. DNL—12-Bit DAC
500
1000
1500
2000 2500
CODE
3000
3500
4000
Figure 15. INL—12-Bit DAC, 1.25 V Internal Reference
0.20
1.0
VDD = 5V
VREFOUT = 2.5V
TA = 25°C
0.8
0.6
VDD = 3V
VREFOUT = 1.25V
TA = 25°C
0.15
0.10
DNL ERROR (LSB)
0.4
0.2
0
–0.2
–0.4
0.05
0
–0.05
–0.10
–0.6
05299-047
INL ERROR (LSB)
500
1.0
0.10
–0.20
0
Figure 14. DNL 12-Bit DAC, 2.5 V Internal Reference
VDD = VREF = 5V
TA = 25°C
0.15
05299-048
–0.8
–0.8
–1.0
0
500
1000
1500
2000 2500
CODE
3000
3500
–0.15
05299-050
INL ERROR (LSB)
0.4
–1.0
VDD = 5V
VREFOUT = 2.5V
TA = 25°C
0.15
0.6
–0.20
0
4000
500
1000
1500
2000 2500
CODE
3000
3500
Figure 16. DNL—12-Bit DAC, 1.25 V Internal Reference
Figure 13. INL—12-Bit DAC, 2.5 V Internal Reference
Rev. C | Page 12 of 28
4000
AD5678
1.0
0
–0.02
TA = 25°C
VDD = 5V
0.5
–0.04
GAIN ERROR
0
ERROR (mV)
ERROR (% FSR)
–0.06
–0.08
–0.10
–0.12
–0.14
ZERO-SCALE ERROR
–0.5
–1.0
–1.5
FULL-SCALE ERROR
–0.20
–40
–2.0
05299-017
–0.18
–20
0
20
40
60
TEMPERATURE (°C)
80
–2.5
2.7
100
Figure 17. Gain Error and Full-Scale Error vs. Temperature
3.2
3.7
4.2
VDD (V)
4.7
5.2
Figure 20. Zero-Scale Error and Offset Error vs. Supply Voltage
20
1.5
1.0
OFFSET ERROR
05299-020
–0.16
18
VDD = 3.6V
VDD = 5.5V
ZERO-SCALE ERROR
16
14
0
FREQUENCY
ERROR (mV)
0.5
–0.5
–1.0
12
10
8
6
–1.5
2
05299-018
–20
0
20
40
60
TEMPERATURE (°C)
80
0
100
Figure 18. Zero-Scale Error and Offset Error vs. Temperature
Figure 21. IDD Histogram with External Reference
1.0
14
12
0.5
VDD = 3.6V
VDD = 5.5V
10
FREQUENCY
FULL-SCALE ERROR
–0.5
–1.0
VREFOUT = 1.25V
VREFOUT = 2.5V
8
6
4
–1.5
05299-019
ERROR (% FSR)
GAIN ERROR
0
–2.0
2.7
1.20 1.22 1.24 1.26 1.28 1.30 1.32 1.34 1.36 1.38 1.40 1.42 1.44
IDD (mA)
3.2
3.7
4.2
VDD (V)
4.7
5.2
2
0
05299-022
–2.5
–40
05299-021
4
OFFSET ERROR
–2.0
2.02 2.04 2.06 2.08 2.10 2.12 2.14 2.16 2.18 2.20 2.22 2.24 2.26 2.28
IDD (mA)
Figure 22. IDD Histogram with Internal Reference
Figure 19. Gain Error and Full-Scale Error vs. Supply Voltage
Rev. C | Page 13 of 28
AD5678
0.50
2.0
DAC LOADED WITH
FULL-SCALE
SOURCING CURRENT
0.40
DAC LOADED WITH
ZERO-SCALE
SINKING CURRENT
VDD = VREF = 5V
1.6
0.30
1.4
0.20
0.10
IDD (mA)
VDD = 3V
VREFOUT = 1.25V
0
–0.10
1.2
VDD = VREF = 3V
1.0
0.8
0.6
–0.20
–0.40
–0.50
–10
–8
–6
–4
–2
0
2
CURRENT (mA)
4
6
8
05299-026
0.4
VDD = 5V
VREFOUT = 2.5V
–0.30
05299-023
ERROR VOLTAGE (V)
TA = 25°C
1.8
0.2
0
512
10
Figure 23. Headroom at Rails vs. Source and Sink
10512
20512
1.6
5.00
1.4
1.2
3/4 SCALE
VDD = VREFIN = 3.6V
3.00
IDD (mA)
1.0
MIDSCALE
2.00
1/4 SCALE
0.8
0.6
1.00
0.4
–1.00
–30
–20
–10
0
10
CURRENT (mA)
20
0.2
0
–40
30
Figure 24. AD5678-2 Source and Sink Capability
1.6
VDD = 3V
VREFOUT = 1.25V
TA = 25°C
20
40
60
TEMPERATURE (°C)
80
100
TA = 25°C
1.2
1.0
IDD (mA)
3/4 SCALE
MIDSCALE
1.00
0
1.4
FULL SCALE
2.00
–20
Figure 27. Supply Current vs. Temperature
4.00
3.00
05299-027
ZERO SCALE
05299-024
0
0.8
0.6
1/4 SCALE
0.4
0
–1.00
–30
05299-025
ZERO SCALE
–20
–10
0
10
CURRENT (mA)
20
30
Figure 25. AD5678-1 Source and Sink Capability
0.2
0
2.7
05299-028
VOUT (V)
60512
VDD = VREFIN = 5.5V
FULL SCALE
4.00
VOUT (V)
50512
Figure 26. Supply Current vs. Code
6.00
VDD = 5V
VREFOUT = 2.5V
TA = 25°C
30512
40512
CODE
3.2
3.7
4.2
VDD (V)
4.7
Figure 28. Supply Current vs. Supply Voltage
Rev. C | Page 14 of 28
5.2
AD5678
8
TA = 25°C
VDD = VREF = 5V
TA = 25°C
7
6
5
IDD (mA)
VDD
4
1
VDD = 5V
3
2
VDD = 3V
0
1
2
3
VLOGIC (V)
4
5
05299-032
0
2
05299-029
1
VOUT
6
CH1 2.0V
CH2 1.0V
M100μs 125MS/s
A CH1
1.28V
8.0ns/pt
Figure 32. Power-On Reset to Midscale
Figure 29. Supply Current vs. Logic Input Voltage
SYNC
1
SLCK
3
VDD = VREF = 5V
TA = 25°C
FULL-SCALE CODE CHANGE
0x0000 TO 0xFFFF
OUTPUT LOADED WITH 2kΩ
AND 200pF TO GND
VOUT
VOUT = 909mV/DIV
1
VDD = 5V
05299-033
05299-030
2
CH1 5.0V
CH3 5.0V
TIME BASE = 4μs/DIV
Figure 30. Full-Scale Settling Time, 5 V
MAX(C2)*
420.0mV
05299-031
2
VOUT
M100μs 125MS/s
A CH1
1.28V
A CH1
1.4V
8.0ns/pt
2.505
2.504
2.503
2.502
2.501
2.500
2.499
2.498
2.497
2.496
2.495
2.494
2.493
2.492
2.491
2.490
2.489
2.488
2.487
2.486
2.485
VDD = 5V
VREFOUT = 2.5V
TA = 25°C
4ns/SAMPLE NUMBER
GLITCH IMPULSE = 3.55nV-s
1 LSB CHANGE AROUND
MIDSCALE (0x8000 TO 0x7FFF)
05299-034
VOUT (V)
VDD
1
CH2 500mV
M400ns
Figure 33. Exiting Power-Down to Midscale
VDD = VREF = 5V
TA = 25°C
CH1 2.0V
CH2 500mV
0
64
128
192
256
320
SAMPLE
384
448
Figure 34. Digital-to-Analog Glitch Impulse (Negative)
Figure 31. Power-On Reset to 0 V
Rev. C | Page 15 of 28
512
AD5678
2.5000
VDD = 5V
VREFOUT = 2.5V
TA = 25°C
DAC LOADED WITH MIDSCALE
2.4995
2.4990
2.4980
10μV/DIV
VOUT (V)
2.4985
2.4975
2.4970
1
2.4965
2.4950
0
64
128
192
256
320
SAMPLE
384
05299-035
VDD = 5V
VREFOUT = 2.5V
TA = 25°C
4ns/SAMPLE NUMBER
2.4955
05299-038
2.4960
512
448
5s/DIV
Figure 38. 0.1 Hz to 10 Hz Output Noise Plot, Internal Reference
Figure 35. Analog Crosstalk
2.4900
VDD = 3V
VREFOUT = 1.25V
TA = 25°C
DAC LOADED WITH MIDSCALE
2.4895
2.4890
5μV/DIV
2.4880
2.4875
1
2.4870
2.4855
0
64
128
192
256
320
SAMPLE
384
448
05299-036
VDD = 5V
VREFOUT = 2.5V
TA = 25°C
4ns/SAMPLE NUMBER
2.4860
05299-039
2.4865
512
4s/DIV
Figure 39. 0.1 Hz to 10 Hz Output Noise Plot, Internal Reference
Figure 36. DAC-to-DAC Crosstalk
800
TA = 25°C
MIDSCALE LOADED
700
1
600
500
400
300
VDD = 5V
VREFOUT = 2.5V
200
VDD = 3V
VREFOUT = 1.25V
100
Y AXIS = 2μV/DIV
X AXIS = 4s/DIV
0
100
Figure 37. 0.1 Hz to 10 Hz Output Noise Plot, External Reference
1000
05299-040
OUTPUT NOISE (nV/√Hz)
VDD = VREF = 5V
TA = 25°C
DAC LOADED WITH MIDSCALE
05299-037
VOUT (V)
2.4885
10000
FREQUENCY (Hz)
100000
Figure 40. Noise Spectral Density, Internal Reference
Rev. C | Page 16 of 28
1000000
AD5678
–20
VDD = 5V
TA = 25°C
DAC LOADED WITH FULL SCALE
VREF = 2V ± 0.3V p-p
–30
–40
CLR
3
VOUT F
(dB)
–50
–60
–70
–80
VOUT B
–100
2k
4k
6k
FREQUENCY (Hz)
8k
05299-043
4
05299-041
–90
2
10k
CH3 5.0V
Figure 41. Total Harmonic Distortion
CH2 1.0V
CH4 1.0V
M200ns A CH3
1.10V
Figure 43. Hardware CLR
16
5
VREF = VDD
TA = 25°C
VDD = 5V
TA = 25°C
0
14
–5
VDD = 3V
(dB)
–10
10
VDD = 5V
8
–15
–20
–25
–30
6
0
1
2
3
4
5
6
7
CAPACITANCE (nF)
8
9
10
Figure 42. Settling Time vs. Capacitive Load
–35
–40
10k
05299-044
4
05299-042
TIME (μs)
12
100k
1M
FREQUENCY (Hz)
Figure 44. Multiplying Bandwidth
Rev. C | Page 17 of 28
10M
AD5678
TERMINOLOGY
Relative Accuracy
For the DAC, relative accuracy, or integral nonlinearity (INL), is
a measure of the maximum deviation in LSBs from a straight
line passing through the endpoints of the DAC transfer
function. Figure 5, Figure 7, and Figure 9 show plots of typical
INL vs. code.
Full-Scale Error
Full-scale error is a measure of the output error when full-scale
code (0xFFFF) is loaded into the DAC register. Ideally, the
output should be VDD − 1 LSB. Full-scale error is expressed as a
percentage of the full-scale range. Figure 17 shows a plot of
typical full-scale error vs. temperature.
Differential Nonlinearity
Differential nonlinearity (DNL) 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. Figure 6, Figure 8, and Figure 10 show plots of
typical DNL vs. code.
Digital-to-Analog Glitch Impulse
Offset Error
Offset error is a measure of the difference between the actual
VOUT and the ideal VOUT, expressed in millivolts in the linear
region of the transfer function. Offset error is measured on the
AD5678 with Code 512 loaded into the DAC register. It can be
negative or positive and is expressed in millivolts.
DC Power Supply Rejection Ratio (PSRR)
PSRR indicates how the output of the DAC is affected by changes
in the supply voltage. PSRR is the ratio of the change in VOUT to
a change in VDD for full-scale output of the DAC. It is measured
in decibels. VREF is held at 2 V, and VDD is varied ±10%.
Zero-Code Error
Zero-code error is a measure of the output error when zero
code (0x0000) is loaded into the DAC register. Ideally, the
output should be 0 V. The zero-code error is always positive in
the AD5678, 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
output amplifier. Zero-code error is expressed in millivolts.
Figure 18 shows a plot of typical zero-code error vs.
temperature.
Gain Error
Gain error is a measure of the span error of the DAC. It is the
deviation in slope of the DAC transfer characteristic from the
ideal, expressed as a percentage of the full-scale range.
Zero-Code Error Drift
Zero-code error drift is a measure of the change in zero-code
error with a change in temperature. It is expressed in μV/°C.
Gain Error Drift
Gain error drift is a measure of the change in gain error with
changes in temperature. It is expressed in (ppm of full-scale
range)/°C.
Digital-to-analog glitch impulse 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 nV-s
and is measured when the digital input code is changed by
1 LSB at the major carry transition (0x7FFF to 0x8000). See
Figure 34.
DC Crosstalk
DC crosstalk is the dc change in the output level of one DAC in
response to a change in the output of another DAC. It is measured
with a full-scale output change on one DAC (or soft power-down
and power-up) while monitoring another DAC. It is expressed
in microvolts.
DC crosstalk due to load current change is a measure of the
impact that a change in load current on one DAC has to another
DAC kept at midscale. It is expressed in microvolts per milliamp.
Reference Feedthrough
Reference feedthrough is the ratio of the amplitude of the signal
at the DAC output to the reference input when the DAC output
is not being updated (that is, LDAC is high). It is expressed in
decibels.
Channel-to-Channel Isolation
Channel-to-channel isolation is the ratio of the amplitude of the
signal at the output of one DAC to a sine wave on the reference
input of another DAC. It is measured in decibels.
Digital Feedthrough
Digital feedthrough is a measure of the impulse injected into
the analog output of a DAC from the digital input pins of the
device, but is measured when the DAC is not being written to
(SYNC held high). It is specified in nV-s and measured with a
full-scale change on the digital input pins, that is, from all 0s to
all 1s or vice versa.
Rev. C | Page 18 of 28
AD5678
Digital Crosstalk
Digital crosstalk is the glitch impulse transferred to the output
of one DAC at midscale in response to a full-scale code change
(all 0s to all 1s or vice versa) in the input register of another
DAC. It is measured in standalone mode and is expressed in
nV-s.
Multiplying Bandwidth
The amplifiers within the DAC have a finite bandwidth. The
multiplying bandwidth is a measure of this. A sine wave on the
reference (with full-scale code loaded to the DAC) appears on
the output. The multiplying bandwidth is the frequency at
which the output amplitude falls to 3 dB below the input.
Analog Crosstalk
Analog crosstalk is the glitch impulse transferred to the output
of one DAC due to a change in the output of another DAC. It is
measured by loading one of the input registers with a full-scale
code change (all 0s to all 1s or vice versa) while keeping LDAC
high, and then pulsing LDAC low and monitoring the output of
the DAC whose digital code has not changed. The area of the
glitch is expressed in nV-s.
Total Harmonic Distortion (THD)
Total harmonic distortion 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, and the THD is a
measure of the harmonics present on the DAC output. It is
measured in decibels.
DAC-to-DAC Crosstalk
DAC-to-DAC crosstalk is the glitch impulse transferred to the
output of one DAC due to a digital code change and subsequent
output change of another DAC. This includes both digital and
analog crosstalk. It is measured by loading one of the DACs
with a full-scale code change (all 0s to all 1s or vice versa) with
LDAC low and monitoring the output of another DAC. The
energy of the glitch is expressed in nV-s.
Rev. C | Page 19 of 28
AD5678
THEORY OF OPERATION
D/A SECTION
R
The AD5678 DAC is fabricated on a CMOS process. The architecture consists of a string of DACs followed by an output buffer
amplifier. The parts include an internal 1.25 V/2.5 V, 5 ppm/°C
reference with an internal gain of 2. Figure 45 shows a block
diagram of the DAC architecture.
R
TO OUTPUT
AMPLIFIER
R
VDD
REF (+)
RESISTOR
STRING
R
OUTPUT
AMPLIFIER
(GAIN = +2)
GND
R
05299-006
REF (–)
VOUT
05299-005
DAC REGISTER
Figure 45. DAC Architecture
Because the input coding to the DAC is straight binary, the ideal
output voltage when using an external reference is given by
Figure 46. Resistor String
INTERNAL REFERENCE
D
VOUT = VREFIN × ⎛⎜ N ⎞⎟
⎝2 ⎠
The AD5678 has an on-chip reference with an internal gain of
2. The AD5678-1 has a 1.25 V 5 ppm/°C reference, giving a fullscale output of 2.5 V. The AD5678-2 has a 2.5 V 5 ppm/°C
reference, giving a full-scale output of 5 V. The on-board
reference is off at power-up, allowing the use of an external
reference. The internal reference is enabled via a write to a
control register. See Table 7.
the ideal output voltage when using an internal reference is
given by
D
VOUT = 2 × V REFOUT × ⎛⎜ N ⎞⎟
⎝2 ⎠
where:
D = decimal equivalent of the binary code that is loaded to the
DAC register.
0 to 4,095 for AD5678 DAC C, D, E, F (12 bits).
0 to 65,535 for AD5678 DAC A, B, G, H (16 bits).
N = the DAC resolution.
The internal reference associated with each part is available at
the VREFOUT pin. A buffer is required if the reference output is
used to drive external loads. When using the internal reference,
it is recommended that a 100 nF capacitor be placed between
the reference output and GND for reference stability.
RESISTOR STRING
Individual channel power-down is not supported while using
the internal reference.
The resistor string section is shown in Figure 46. It is simply a
string of resistors, each of value R. The code loaded into 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.
Rev. C | Page 20 of 28
AD5678
Table 7. Command Definitions
OUTPUT AMPLIFIER
The output buffer amplifier can generate rail-to-rail voltages on
its output, which gives an output range of 0 V to VDD. The
amplifier is capable of driving a load of 2 kΩ in parallel with
1,000 pF to GND. The source and sink capabilities of the output
amplifier can be seen in Figure 24 and Figure 25. The slew rate
is 1.5 V/μs with a ¼ to ¾ scale settling time of 10 μs.
SERIAL INTERFACE
The AD5678 has a 3-wire serial interface (SYNC, SCLK, and
DIN) that is compatible with SPI, QSPI, and MICROWIRE
interface standards as well as most DSPs. See Figure 2 for a
timing diagram of a typical write sequence.
The write sequence begins by bringing the SYNC line low. Data
from the DIN line is clocked into the 32-bit shift register on the
falling edge of SCLK. The serial clock frequency can be as high
as 50 MHz, making the AD5678 compatible with high speed
DSPs. On the 32nd falling clock edge, the last data bit is clocked
in and the programmed function is executed, that is, a change
in DAC register contents and/or a change in the mode of
operation. At this stage, the SYNC line can be kept low or be
brought high. In either case, it must be brought high for a
minimum of 15 ns before the next write sequence so that a
falling edge of SYNC can initiate the next write sequence.
Because the SYNC buffer draws more current when VIN = 2 V
than it does when VIN = 0.8 V, SYNC should be idled low
between write sequences for even lower power operation of the
part. As is mentioned previously, however, SYNC must be
brought high again just before the next write sequence.
C3
0
0
0
0
0
0
0
0
1
1
–
1
Command
C2 C1
0
0
0
0
0
1
0
1
1
1
1
0
0
–
1
1
0
0
1
1
0
0
–
1
C0
0
1
0
1
0
1
0
1
0
1
–
1
Description
Write to Input Register n
Update DAC Register n
Write to Input Register n, update all
(software LDAC)
Write to and update DAC Channel n
Power down/power up DAC
Load clear code register
Load LDAC register
Reset (power-on reset)
Set up internal REF register
Reserved
Reserved
Reserved
Table 8. Address Commands
A3
0
0
0
0
0
0
0
0
1
Rev. C | Page 21 of 28
A2
0
0
0
0
1
1
1
1
1
Address (n)
A1
0
0
1
1
0
0
1
1
1
A0
0
1
0
1
0
1
0
1
1
Selected DAC
Channel
DAC A (16 bits)
DAC B (16 bits)
DAC C (12 bits)
DAC D (12 bits)
DAC E (12 bits)
DAC F (12 bits)
DAC G (16 bits)
DAC H (16 bits)
All DACs
AD5678
INPUT SHIFT REGISTER
SYNC INTERRUPT
The input shift register is 32 bits wide. The first four bits are
don’t cares. The next four bits are the command bits, C3 to C0
(see Table 7), followed by the 4-bit DAC address bits, A3 to A0
(see Table 8), and finally the 16-/12-bit data-word. The dataword comprises the 16-/12-bit input code followed by four or
eight don’t care bits for the AD5678 DAC A, B, G, H and
AD5678 DAC C, D, E, F, respectively (See Figure 47 and
Figure 48). These data bits are transferred to the DAC register
on the 32nd falling edge of SCLK.
In a normal write sequence, the SYNC line is kept low for
32 falling edges of SCLK, and the DAC is updated on the 32nd
falling edge and rising edge of SYNC. However, if SYNC is
brought high before the 32nd 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 49.
DB31 (MSB)
X
X
DB0 (LSB)
X
X
C3
C2
C1
C0
A3
A2
A1
A0
D15 D14 D13 D12 D11 D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
X
X
X
X
COMMAND BITS
05299-007
DATA BITS
ADDRESS BITS
Figure 47. AD5678 Input Register Content for DAC A, B, G , H
DB31 (MSB)
X
X
X
C3
C2
C1
C0
A3
A2
A1
A0
D11 D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
X
X
X
X
X
X
X
X
COMMAND BITS
05299-008
DATA BITS
ADDRESS BITS
Figure 48. AD5678 Input Register Content for DAC C, D, E, F
SCLK
SYNC
DIN
DB31
DB0
INVALID WRITE SEQUENCE:
SYNC HIGH BEFORE 32ND FALLING EDGE
DB31
DB0
VALID WRITE SEQUENCE, OUTPUT UPDATES
ON THE 32ND FALLING EDGE
Figure 49. SYNC Interrupt Facility
Rev. C | Page 22 of 28
05299-009
X
DB0 (LSB)
AD5678
INTERNAL REFERENCE REGISTER
The on-board reference is off at power-up by default. This
allows the use of an external reference if the application requires
it. The on-board reference can be turned on/off by a userprogrammable internal REF register by setting Bit DB0 high or
low (see Table 9). Command 1000 is reserved for this internal
REF set-up command (see Table 7). Table 11 shows the state of
the bits in the input shift register corresponds to the mode of
operation of the device.
POWER-ON RESET
The AD5678 contains a power-on reset circuit that controls the
output voltage during power-up. The AD5678 output powers up
to 0 V, and the output remains powered up at this level until a
valid write sequence is made to the DAC. This is useful in
applications where it is important to know the state of the
output of the DAC while it is in the process of powering up.
There is also a software executable reset function that resets the
DAC to the power-on reset code. Command 0111 is reserved
for this reset function—see Table 7. Any events on LDAC or
CLR during power-on reset are ignored.
POWER-DOWN MODES
The AD5678 contains four separate modes of operation.
Command 0100 is reserved for the power-down function. See
Table 7. These modes are software-programmable by setting
two bits, Bit DB9 and Bit DB8, in the control register.
Table 11 shows how the state of the bits corresponds to the
mode of operation of the device. Any or all DACs (DAC H to
DAC A) can be powered down to the selected mode by setting
the corresponding eight bits (DB7 to DB0) to 1. See Table 12 for
the contents of the input shift register during power-down/powerup operation. When using the internal reference, only all channel
power-down to the selected modes is supported.
When both bits are set to 0, the part works normally with its
normal power consumption of 1.3 mA at 5 V. However, for the
three power-down modes, the supply current falls to 400 nA at
5 V (200 nA at 3 V). Not only does the supply current fall, but
the output stage is also internally switched from the output of
the amplifier to a resistor network of known values. This has the
advantage that the output impedance of the part is known while
the part is in power-down mode. There are three different
options. The output is connected internally to GND through
either a 1 kΩ or a 100 kΩ resistor, or it is left open-circuited
(three-state). The output stage is illustrated in Figure 50.
The bias generator of the selected DAC(s), output amplifier,
resistor string, and other associated linear circuitry are shut
down when the power-down mode is activated. However, the
contents of the DAC register are unaffected when in powerdown. The time to exit power-down is typically 5 μs for
VDD = 5 V and for VDD = 3 V, see Figure 33.
Any combination of DACs can be powered up by setting PD1
and PD0 to 0 (normal operation). The output powers up to the
value in the input register (LDAC low) or to the value in the
DAC register before powering down (LDAC high).
CLEAR CODE REGISTER
The AD5678 has a hardware CLR pin that is an asynchronous
clear input. The CLR input is falling edge sensitive . Bringing
the CLR line low clears the contents of the input register and the
DAC registers to the data contained in the user-configurable
CLR register and sets the analog outputs accordingly. This
function can be used in system calibration to load zero scale,
midscale, or full scale to all channels together. These clear code
values are user-programmable by setting two bits, Bit DB1 and Bit
DB0, in the CLR control register. See Table 13. The default
setting clears the outputs to 0 V. Command 0101 is reserved for
loading the clear code register, see Table 7.
The part exits clear code mode on the 32nd falling edge of the
next write to the part. If CLR is activated during a write
sequence, the write is aborted.
The CLR pulse activation time—the falling edge of CLR to when
the output starts to change—is typically 280 ns. However, if the
value is outside the linear region, it typically takes 520 ns after
executing CLR for the output to start changing. See Figure 43.
See Table 14 for contents of the input shift register during the
loading clear code register operation.
Rev. C | Page 23 of 28
AD5678
Table 9. Internal Reference Register
Internal REF Register (DB0)
0
1
Action
Reference off (default)
Reference on
Table 10. 32-Bit Input Shift Register Contents for Reference Set-Up Function
MSB
DB31 to DB28
X
Don’t cares
DB27
DB26
DB25
DB24
1
0
0
0
Command bits (C3 to C0)
DB23
X
DB22
DB21
DB20
X
X
X
Address bits (A3 to A0)
DB19 to DB1
X
Don’t cares
LSB
DB0
1/0
Internal REF
register
Table 11. Power-Down Modes of Operation
DB9
0
DB8
0
0
1
1
1
0
1
Operating Mode
Normal operation
Power-down modes
1 kΩ to GND
100 kΩ to GND
Three-state
Table 12. 32-Bit Input Shift Register Contents for Power-Down/Power-Up Function
MSB
DB31
to
DB28
X
Don’t
cares
LSB
DB27
0
DB26
1
DB25
0
Command bits (C3 to C0)
DB24
0
DB23
X
DB22
X
DB21
X
DB20
X
Address bits (A3 to A0)—
don’t cares
DB19
to
DB10
X
DB9
PD1
Don’t
cares
Powerdown mode
DB8
PD0
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DAC
DAC
DAC
DAC
DAC
DAC
DAC
DAC
H
G
F
E
D
C
B
A
Power-down/power-up channel selection—set bit to 1 to select
VFB
AMPLIFIER
VOUT
POWER-DOWN
CIRCUITRY
RESISTOR
NETWORK
05299-010
RESISTOR
STRING DAC
Figure 50. Output Stage During Power-Down
Table 13. Clear Code Register
DB1
CR1
0
0
1
1
Clear Code Register
DB0
CR0
0
1
0
1
Clears to Code
0x0000
0x8000
0xFFFF
No operation
Table 14. 32-Bit Input Shift Register Contents for Clear Code Function
MSB
DB31 to DB28
X
Don’t cares
DB27
DB26
DB25
DB24
0
1
0
1
Command bits (C3 to C0)
DB23
DB22
DB21
DB20
X
X
X
X
Address bits (A3 to A0)—don’t cares
Rev. C | Page 24 of 28
DB19 to DB2
X
Don’t cares
LSB
DB1
DB0
CR1
CR0
Clear code register
AD5678
LDAC FUNCTION
POWER SUPPLY BYPASSING AND GROUNDING
The outputs of all DACs can be updated simultaneously using
the hardware LDAC pin.
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 AD5678 should
have separate analog and digital sections. If the AD5678 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 AD5678.
Synchronous LDAC: After new data is read, the DAC registers
are updated on the falling edge of the 32nd SCLK pulse. LDAC
can be permanently low or pulsed as in Figure 2.
Asynchronous LDAC: The outputs are not updated at the same
time that the input registers are written to. When LDAC goes low,
the DAC registers are updated with the contents of the input register.
Alternatively, the outputs of all DACs can be updated simultaneously using the software LDAC function by writing to Input
Register n and updating all DAC registers. Command 0011 is
reserved for this software LDAC function.
An LDAC register gives the user extra flexibility and control
over the hardware LDAC pin. This register allows the user to
select which combination of channels to simultaneously update
when the hardware LDAC pin is executed. Setting the LDAC bit
register to 0 for a DAC channel means that this channel’s update
is controlled by the LDAC pin. If this bit is set to 1, this channel
updates synchronously; that is, the DAC register is updated
after new data is read, regardless of the state of the LDAC pin. It
effectively sees the LDAC pin as being tied low. (See Table 15
for the LDAC register mode of operation.) This flexibility is
useful in applications where the user wants to simultaneously
update select channels while the rest of the channels are
synchronously updating.
The power supply to the AD5678 should be bypassed with 10 μF
and 0.1 μF capacitors. The capacitors should physically be 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 low effective series inductance (ESI),
such as is typical of 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.
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, ensure that they run at right
angles to each other to reduce feedthrough effects through 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.
Writing to the DAC using command 0110 loads the 8-bit LDAC
register (DB7 to DB0). The default for each channel is 0; that is,
the LDAC pin works normally. Setting the bits to 1 means the
DAC channel is updated regardless of the state of the LDAC
pin. See Table 16 for the contents of the input shift register
during the load LDAC register mode of operation.
Table 15. LDAC Register
Load DAC Register
LDAC Bits (DB7 to DB0)
LDAC Pin
LDAC Operation
0
1
Determined by LDAC pin
DAC channels update, overriding the LDAC pin. DAC channels see LDAC as 0.
1/0
X—don’t care
Table 16. 32-Bit Input Shift Register Contents for LDAC Overwrite Function
MSB
DB31
to
DB28
X
Don’t
cares
LSB
DB27
0
DB26
1
DB25
1
DB24
0
Command bits (C3 to C0)
DB23
X
DB22
X
DB21
X
Address bits (A3 to A0)—
don’t cares
DB20
X
DB19
to
DB8
X
Don’t
cares
Rev. C | Page 25 of 28
DB7
DAC
H
DB6
DAC
G
DB5
DB4
DB3
DB2
DB1
DAC
DAC
DAC
DAC
DAC
F
E
D
C
B
Setting LDAC bit to 1 overrides LDAC pin
DB0
DAC
A
AD5678
OUTLINE DIMENSIONS
5.10
5.00
4.90
14
8
4.50
4.40
4.30
6.40
BSC
1
7
PIN 1
0.65 BSC
1.20
MAX
0.15
0.05
COPLANARITY
0.10
0.20
0.09
SEATING
PLANE
0.30
0.19
0.75
0.60
0.45
8°
0°
061908-A
1.05
1.00
0.80
COMPLIANT TO JEDEC STANDARDS MO-153-AB-1
Figure 51. 14-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-14)
Dimensions shown in millimeters
5.10
5.00
4.90
16
9
4.50
4.40
4.30
6.40
BSC
1
8
PIN 1
1.20
MAX
0.15
0.05
0.65
BSC
0.30
0.19
COPLANARITY
0.10
0.20
0.09
SEATING
PLANE
0.75
0.60
0.45
8°
0°
COMPLIANT TO JEDEC STANDARDS MO-153-AB
Figure 52. 16-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-16)
Dimensions shown in millimeters
ORDERING GUIDE
Model 1
AD5678BRUZ-1
AD5678BRUZ-1REEL7
AD5678BRUZ-2
AD5678BRUZ-2REEL7
AD5678ARUZ-2
AD5678ARUZ-2REEL7
1
Temperature Range
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
Package Description
14-Lead TSSOP
14-Lead TSSOP
16-Lead TSSOP
16-Lead TSSOP
16-Lead TSSOP
16-Lead TSSOP
Z = RoHS Compliant Part.
Rev. C | Page 26 of 28
Package
Option
RU-14
RU-14
RU-16
RU-16
RU-16
RU-16
Power-On
Reset to Code
Zero
Zero
Zero
Zero
Zero
Zero
Accuracy
±16 LSB INL
±16 LSB INL
±16 LSB INL
±16 LSB INL
±32 LSB INL
±32 LSB INL
Internal
Reference
1.25 V
1.25 V
2.5 V
2.5 V
2.5 V
2.5 V
AD5678
NOTES
Rev. C | Page 27 of 28
AD5678
NOTES
©2005–2011 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D05299–0–2/11(C)
Rev. C | Page 28 of 28
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