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4 x 12-Bit and 4 x 16-Bit Octal DAC with On-Chip Reference in 14-Lead TSSOP AD5678
FEATURES
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
AD5678
LDAC INPUT REGISTER INPUT REGISTER SCLK INTERFACE LOGIC INPUT REGISTER INPUT REGISTER INPUT REGISTER INPUT REGISTER INPUT REGISTER INPUT REGISTER POWER-ON RESET LDAC1 CLR1
1RU-16
FUNCTIONAL BLOCK DIAGRAM
VDD VREFIN/VREFOUT 1.25V/2.5V REF DAC REGISTER DAC REGISTER DAC REGISTER DAC REGISTER DAC REGISTER DAC REGISTER DAC REGISTER DAC REGISTER STRING DAC A STRING DAC B STRING DAC C STRING DAC D STRING DAC E STRING DAC F STRING DAC G STRING DAC H BUFFER VOUTA
BUFFER
VOUTB
BUFFER
VOUTC
SYNC
BUFFER
VOUTD
DIN
BUFFER
VOUTE
BUFFER
VOUTF
BUFFER
VOUTG
BUFFER VOUTH POWER-DOWN LOGIC GND
05299-001
APPLICATIONS
Process control Data acquisition systems Portable battery-powered instruments Digital gain and offset adjustment Programmable voltage current sources Programmable attenuators
PACKAGE ONLY
Figure 1.
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(R), QSPITM, MICROWIRETM, 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. A
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 (c) 2005 Analog Devices, Inc. All rights reserved.
AD5678 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Product Highlights ........................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 AC Characteristics........................................................................ 7 Timing Characteristics ................................................................ 8 Absolute Maximum Ratings............................................................ 9 ESD Caution.................................................................................. 9 Pin Configuration and Function Descriptions........................... 10 Typical Performance Characteristics ........................................... 11 Terminology .................................................................................... 18 Theory of Operation ...................................................................... 20 D/A Section................................................................................. 20 Resistor String............................................................................. 20 Internal Reference ...................................................................... 20 Output Amplifier........................................................................ 21 Serial Interface ............................................................................ 21 Input Shift Register .................................................................... 22 SYNC Interrupt .......................................................................... 22 Internal Reference Register....................................................... 23 Power-On Reset.......................................................................... 23 Power-Down Modes .................................................................. 23 Clear Code Register ................................................................... 23 LDAC Function .......................................................................... 25 Power Supply Bypassing and Grounding................................ 25 Outline Dimensions ....................................................................... 26 Ordering Guide .......................................................................... 26
REVISION HISTORY
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. A | Page 2 of 28
AD5678 SPECIFICATIONS
VDD = 4.5 V to 5.5 V, RL = 2 k 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 Unit Conditions/Comments
12 0.5 2 0.25
12 0.5 1 0.25
Bits LSB LSB
See Figure 11 Guaranteed monotonic by design (see Figure 12)
16 8 1 2 -0.2 2.5 1 -80 10 5 10 25 10 9 32 1 9 -1 1
16 8 1 2 -0.2 2.5 1 -80 10 5 10 25 10 VDD 2 10 0.5 30 4 VDD 35 0 2 10 0.5 30 4 VDD 35 0 14.6 VDD 9 16 1 9 -1 1
Bits LSB LSB mV V/C % FSR % FSR ppm mV dB V V/mA V V V/mA V nF nF mA s V A V k
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 k to GND or VDD Due to load current change Due to powering down (per channel) Due to full-scale output change, RL = 2 k to GND or VDD Due to load current change
DC Crosstalk (Internal Reference) OUTPUT CHARACTERISTICS 3 Output Voltage Range Capacitive Load Stability 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
0
RL = RL = 2 k 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
0 14.6
45 VDD
45 VDD
2.495 5 7.5
2.505 10
2.495 5 7.5
2.505 10
V ppm/C k A V V pF
At ambient
3 0.8 2 3 2 3
3 0.8
All digital inputs VDD = 5 V VDD = 5 V
Rev. A | 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
1 2
A Grade 1 Min Typ Max 4.5 5.5
B Grade1 Min Typ Max 4.5 5.5
Unit V
Conditions/Comments All digital inputs at 0 or VDD, DAC active, excludes load current VIH = VDD and VIL = GND Internal reference off Internal reference on VIH = VDD and VIL = GND
1.3 2 0.4
1.8 2.5 1
1.3 2 0.4
1.8 2.5 1
mA mA A
Temperature range is -40C to +105C, typical at 25C. 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.
Rev. A | Page 4 of 28
AD5678
VDD = 2.7 V to 3.6 V, RL = 2 k 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 Unit Conditions/Comments
12 0.5 2 1
12 0.5 1 1
Bits LSB LSB
See Figure 11 Guaranteed monotonic by design (see Figure 12)
16 32 1 9 -1 1 9
16 16 1 9 -1 1 9
1 2 -0.2 2.5 1 1.7 -80 10 4.5 10 25 4.5
1 2 -0.2 2.5 1 1.7 -80 10 4.5 10 25 4.5
Bits LSB LSB mV V/C % FSR % FSR ppm mV V/C dB V V/mA V V V/mA
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 k to GND or VDD Due to load current change Due to powering down (per channel) Due to full-scale output change, RL = 2 k to GND or VDD Due to load current change
DC Crosstalk (Internal Reference) OUTPUT CHARACTERISTICS 3 Output Voltage Range Capacitive Load Stability 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 2 10 0.5 30 4 VDD 20 0 14.6
VDD
0 2 10 0.5 30 4 VDD 20 0 14.6
VDD
V nF nF mA s V A V k
RL = RL = 2 k 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
20 VDD
20 VDD
1.247 5 7.5
1.253 15
1.247 5 7.5
1.253 15
V ppm/C k
At ambient
Rev. A | Page 5 of 28
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
1 2
A Grade 1 Min Typ Max 3 0.8 2 3 2.7 3.6
B Grade1 Min Typ Max 3 0.8 2 3 2.7 3.6
Unit A V V pF V
Conditions/Comments All digital inputs VDD = 3 V VDD = 3 V
1.2 1.7 0.2
1.5 2.25 1
1.2 1.7 0.2
1.5 2.25 1
mA mA A
All digital inputs at 0 or VDD, DAC active, excludes load current VIH = VDD and VIL = GND Internal reference off Internal reference on VIH = VDD and VIL = GND
Temperature range is -40C to +105C, typical at 25C. 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.
Rev. A | Page 6 of 28
AD5678
AC CHARACTERISTICS
VDD = 2.7 V to 5.5 V, RL = 2 k 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
1 2
Min
Typ 6 1.5 4 0.1 -90 0.5 2.5 3 340 -80 120 100 15
Max 10
Unit s V/s nV-s nV-s dB nV-s nV-s nV-s kHz dB nV/Hz nV/Hz V p-p
Conditions/Comments 3 1/4 to 3/4 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
Guaranteed by design and characterization; not production tested. See the Terminology section. 3 Temperature range is -40C to +105C, typical at 25C.
Rev. A | 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.
Parameter t1 1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t12 t13 t14 t15
1
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
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
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
SCLK
t1
t9
t8
SYNC
t4
t3
t2
t7
t5
DIN DB31
t6
DB0
t14
LDAC1
t11
t12
LDAC2 CLR
t13 t15
05299-002
VOUT
1ASYNCHRONOUS LDAC UPDATE MODE. 2SYNCHRONOUS LDAC UPDATE MODE.
Figure 2. Serial Write Operation
Rev. A | Page 8 of 28
AD5678 ABSOLUTE MAXIMUM RATINGS
TA = 25C, 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 JA 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 -40C to +105C -65C to +150C +150C (TJ MAX - TA)/JA 150.4C/W 240C 260C
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
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. A | Page 9 of 28
AD5678 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
LDAC 1
SYNC VDD VOUTA VOUTC VOUTE VOUTG VREFIN/VREFOUT
1 2 3 4 5 6 7 14 13
16 15
SCLK DIN GND VOUTB VOUTD VOUTF VOUTH CLR
05299-004
SCLK DIN GND VOUTB VOUTD VOUTF VOUTH
05299-003
SYNC 2 VDD
3
AD5678
TOP VIEW (Not to Scale)
14 13 12 11 10 9
AD5678
TOP VIEW (Not to Scale)
12 11 10 9 8
VOUTA 4 VOUTC VOUTE VOUTG VREFIN/VREFOUT
5 6 7 8
Figure 3. 14-Lead TSSOP (RU-14)
Figure 4. 16-Lead TSSOP (RU-16)
Table 6. Pin Function Descriptions
Pin No. 14-Lead 16-Lead TSSOP TSSOP - 1
Mnemonic LDAC
Description 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 F capacitor in parallel with a 0.1 F 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.
1
2
SYNC
2 3 11 4 10 7
3 4 13 5 12 8
VDD VOUTA VOUTB VOUTC VOUTD VREFIN/VREFOUT
-
9
CLR
5 9 6 8 12 13 14
6 11 7 10 14 15 16
VOUTE VOUTF VOUTG VOUTH GND DIN SCLK
Rev. A | Page 10 of 28
AD5678 TYPICAL PERFORMANCE CHARACTERISTICS
10 8 6 4
INL ERROR (LSB)
DNL ERROR (LSB)
1.0
VDD = VREF = 5V TA = 25C
0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6
05299-011
VDD = 5V VREFOUT = 2.5V TA = 25C
2 0 -2 -4 -6 -8 -10 0
-0.8 -1.0
0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 55000 60000 65000
5k 10k 15k 20k 25k 30k 35k 40k 45k 50k 55k 60k 65k CODE
CODE
Figure 5. INL--16-Bit DAC
Figure 8. DNL 16-Bit DAC, 2.5 V Internal Reference
10
1.0 0.8 0.6
DNL ERROR (LSB)
VDD = VREF = 5V TA = 25C
8 6
VDD = 3V VREFOUT = 1.25V TA = 25C
0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 0 10k 20k 30k CODE 40k 50k 60k
05299-012
INL ERROR (LSB)
4 2 0 -2 -4 -6 -8 -10
05299-015
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
55000
60000
CODE
Figure 6. DNL--16-Bit DAC
Figure 9. INL--16-Bit DAC, 1.25 V Internal Reference
10 8 6
INL ERROR (LSB)
VDD = 5V VREFOUT = 2.5V TA = 25C
4 2 0 -2 -4 -6 -8 -10
0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 55000 60000 65000
05299-013
CODE
Figure 7. INL--16-Bit DAC, 2.5 V Internal Reference
Rev. A | Page 11 of 28
65000
05299-014
AD5678
1.0 0.8 0.6 VDD = 3V VREFOUT = 1.25V TA = 25C
1.0 0.8 0.6
INL ERROR (LSB)
VDD = 5V VREFOUT = 2.5V TA = 25C
DNL ERROR (LSB)
0.4 0.2 0 -0.2 -0.4 -0.6
05299-016
0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 0 500 1000 1500 2000 2500 CODE 3000 3500 4000
05299-047
-0.8 -1.0
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
55000
60000
CODE
65000
Figure 13. INL--12-Bit DAC, 2.5 V Internal Reference
0.20 0.15 0.10
DNL ERROR (LSB)
Figure 10. DNL--16-Bit DAC, 1.25 V Internal Reference
1.0 VDD = VREF = 5V 0.8 TA = 25C 0.6 0.4
VDD = 5V VREFOUT = 2.5V TA = 25C
INL ERROR (LSB)
0.05 0 -0.05 -0.10
05299-048
0.2 0 -0.2 -0.4 -0.6
-0.15
-0.8 -1.0 0 500 1000 1500 2000 2500 CODE 3000 3500 4000
05299-045
-0.20
0
500
1000
1500
2000 2500 CODE
3000
3500
4000
Figure 14. DNL 12-Bit DAC, 2.5 V Internal Reference
Figure 11. INL--12-Bit DAC
1.0
0.20 0.15 0.10 VDD = VREF = 5V TA = 25C
0.8 0.6
INL ERROR (LSB)
VDD = 3V VREFOUT = 1.25V TA = 25C
0.4 0.2 0 -0.2 -0.4 -0.6 -0.8
05299-049
DNL ERROR (LSB)
0.05 0 -0.05 -0.10
05299-046
-0.15 -0.20
-1.0 0 500 1000 1500 2000 2500 CODE 3000 3500 4000
0
500
1000
1500
2000 2500 CODE
3000
3500
4000
Figure 15. INL--12-Bit DAC, 1.25 V Internal Reference
Figure 12. DNL--12-Bit DAC
Rev. A | Page 12 of 28
AD5678
0.20 0.15 0.10
DNL ERROR (LSB)
1.0
VDD = 3V VREFOUT = 1.25V TA = 25C
0.5 GAIN ERROR
0.05 0 -0.05 -0.10
05299-050
ERROR (% FSR)
0 FULL-SCALE ERROR -0.5
-1.0
-0.20 0 500 1000 1500 2000 2500 CODE 3000 3500 4000
-2.0 2.7
3.2
3.7
4.2 VDD (V)
4.7
5.2
Figure 16. DNL--12-Bit DAC, 1.25 V Internal Reference
0 -0.02 -0.04 -0.06
ERROR (% FSR)
Figure 19. Gain Error and Full-Scale Error vs. Supply Voltage
1.0 TA = 25C 0.5 ZERO-SCALE ERROR
VDD = 5V
GAIN ERROR
ERROR (mV)
0 -0.5 -1.0 -1.5 -2.0 -2.5 2.7
-0.08 -0.10 -0.12 -0.14 -0.16
05299-017
FULL-SCALE ERROR
-0.18 -0.20 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100
3.2
3.7
4.2 VDD (V)
4.7
5.2
Figure 17. Gain Error and Full-Scale Error vs. Temperature
Figure 20. Zero-Scale Error and Offset Error vs. Supply Voltage
1.5 1.0 0.5 ZERO-SCALE ERROR
20 18 16 14
VDD = 3.6V VDD = 5.5V
FREQUENCY
ERROR (mV)
0 -0.5 -1.0 -1.5 OFFSET ERROR
05299-018
12 10 8 6 4 2 0 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)
05299-021
-2.0 -2.5 -40
-20
0
20 40 60 TEMPERATURE (C)
80
100
Figure 18. Zero-Scale Error and Offset Error vs. Temperature
Figure 21. IDD Histogram with External Reference
Rev. A | Page 13 of 28
05299-020
OFFSET ERROR
05299-019
-0.15
-1.5
AD5678
14 12 10 VDD = 3.6V VDD = 5.5V
4.00 VDD = 3V VREFOUT = 1.25V TA = 25C FULL SCALE 3/4 SCALE MIDSCALE 1.00 1/4 SCALE
3.00
VREFOUT = 1.25V 8 6 4 2 0 VREFOUT = 2.5V
FREQUENCY
VOUT (V)
2.00
0
05299-022
ZERO SCALE
05299-025
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)
-1.00 -30
-20
-10
0 10 CURRENT (mA)
20
30
Figure 22. IDD Histogram with Internal Reference
0.50 0.40 0.30
ERROR VOLTAGE (V)
Figure 25. AD5678-1 Source and Sink Capability
2.0 TA = 25C VDD = VREF = 5V
DAC LOADED WITH FULL-SCALE SOURCING CURRENT
DAC LOADED WITH ZERO-SCALE SINKING CURRENT
1.8 1.6 1.4
IDD (mA)
0.20 0.10 0 -0.10 -0.20 -0.30 -0.40 -0.50 -10 -8 -6 -4 -2 0 2 CURRENT (mA) 4 6 8 VDD = 5V VREFOUT = 2.5V VDD = 3V VREFOUT = 1.25V
1.2 1.0 0.8 0.6 0.4
VDD = VREF = 3V
05299-023
0.2 0 512 10512 20512 30512 40512 CODE 50512 60512
10
Figure 23. Headroom at Rails vs. Source and Sink
Figure 26. Supply Current vs. Code
6.00 5.00 4.00 3.00 2.00 1/4 SCALE 1.00 0 -1.00 -30 VDD = 5V VREFOUT = 2.5V TA = 25C FULL SCALE
1.6 1.4
VDD = VREFIN = 5.5V
3/4 SCALE
1.2 1.0 VDD = VREFIN = 3.6V
VOUT (V)
MIDSCALE
IDD (mA)
0.8 0.6 0.4
05299-024
-20
-10
0 10 CURRENT (mA)
20
30
0 -40
-20
0
20 40 60 TEMPERATURE (C)
80
100
Figure 24. AD5678-2 Source and Sink Capability
Figure 27. Supply Current vs. Temperature
Rev. A | Page 14 of 28
05299-027
ZERO SCALE
0.2
05299-026
AD5678
1.6 1.4 1.2 1.0
IDD (mA)
TA = 25C
VDD = VREF = 5V TA = 25C
0.8
VDD
0.6 0.4
05299-028
1
MAX(C2)* 420.0mV VOUT CH1 2.0V CH2 500mV M100s 125MS/s A CH1 1.28V 8.0ns/pt
05299-031
0.2 0 2.7
2
3.2
3.7
4.2 VDD (V)
4.7
5.2
Figure 28. Supply Current vs. Supply Voltage
8 7 6 5 TA = 25C
Figure 31. Power-On Reset to 0 V
VDD = VREF = 5V TA = 25C
IDD (mA)
VDD
4 3 2
05299-029
1
VDD = 5V
0
VDD = 3V 0 1 2 3 VLOGIC (V) 4 5 6
VOUT CH1 2.0V CH2 1.0V M100s 125MS/s A CH1 1.28V 8.0ns/pt
Figure 29. Supply Current vs. Logic Input Voltage
Figure 32. Power-On Reset to Midscale
SYNC 1 3
VDD = VREF = 5V TA = 25C FULL-SCALE CODE CHANGE 0x0000 TO 0xFFFF OUTPUT LOADED WITH 2k AND 200pF TO GND
SLCK
VOUT = 909mV/DIV 1
05299-030
VOUT 2
VDD = 5V
05299-033
TIME BASE = 4s/DIV
CH1 5.0V CH3 5.0V
CH2 500mV
M400ns
A CH1
1.4V
Figure 30. Full-Scale Settling Time, 5 V
Figure 33. Exiting Power-Down to Midscale
Rev. A | Page 15 of 28
05299-032
1
2
AD5678
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 = 25C 4ns/SAMPLE NUMBER GLITCH IMPULSE = 3.55nV-s 1 LSB CHANGE AROUND MIDSCALE (0x8000 TO 0x7FFF)
VDD = VREF = 5V TA = 25C DAC LOADED WITH MIDSCALE
VOUT (V)
1
05299-034
0
64
128
192
256 320 SAMPLE
384
448
512
Figure 34. Digital-to-Analog Glitch Impulse (Negative)
2.5000 2.4995 2.4990 2.4985
VOUT (V)
Figure 37. 0.1 Hz to 10 Hz Output Noise Plot, External Reference
VDD = 5V VREFOUT = 2.5V TA = 25C DAC LOADED WITH MIDSCALE
2.4980 2.4975 2.4970 2.4965 2.4960 2.4955 2.4950 0 64 128 192 VDD = 5V VREFOUT = 2.5V TA = 25C 4ns/SAMPLE NUMBER 256 320 SAMPLE 384 448
10V/DIV
1
05299-035
05299-037
Y AXIS = 2V/DIV X AXIS = 4s/DIV
512
5s/DIV
Figure 35. Analog Crosstalk
Figure 38. 0.1 Hz to 10 Hz Output Noise Plot, Internal Reference
2.4900 2.4895 2.4890 2.4885
VOUT (V)
5V/DIV
VDD = 3V VREFOUT = 1.25V TA = 25C DAC LOADED WITH MIDSCALE
2.4880 2.4875 2.4870 2.4865 2.4860 2.4855 VDD = 5V VREFOUT = 2.5V TA = 25C 4ns/SAMPLE NUMBER 0 64 128 192 256 320 SAMPLE 384 448
1
05299-036
512
4s/DIV
Figure 36. DAC-to-DAC Crosstalk
Figure 39. 0.1 Hz to 10 Hz Output Noise Plot, Internal Reference
Rev. A | Page 16 of 28
05299-039
05299-038
AD5678
800 700
OUTPUT NOISE (nV/Hz)
TA = 25C MIDSCALE LOADED
3 CLR
600 500 400 300 200 100 0 100 VDD = 3V VREFOUT = 1.25V 1000 10000 FREQUENCY (Hz) 100000 VDD = 5V VREFOUT = 2.5V
05299-040
VOUT F
VOUT B
05299-043
4 2 CH3 5.0V CH2 1.0V CH4 1.0V M200ns A CH3 1.10V
1000000
Figure 40. Noise Spectral Density, Internal Reference
-20 -30 -40 -50
(dB)
Figure 43. Hardware CLR
VDD = 5V TA = 25C DAC LOADED WITH FULL SCALE VREF = 2V 0.3V p-p
5 0 -5
VDD = 5V TA = 25C
-60
-10
-70 -80
05299-041
(dB)
-15 -20 -25 -30
05299-044
-90 -100
2k
4k 6k FREQUENCY (Hz)
8k
10k
-35 -40 10k
Figure 41. Total Harmonic Distortion
100k 1M FREQUENCY (Hz)
10M
Figure 44. Multiplying Bandwidth
16 VREF = VDD TA = 25C 14 VDD = 3V 12
TIME (s)
10 VDD = 5V
8
6
05299-042
4
0
1
2
3
4 5 6 7 CAPACITANCE (nF)
8
9
10
Figure 42. Settling Time vs. Capacitive Load
Rev. A | Page 17 of 28
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. 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. 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. 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 V/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. 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. Digital-to-Analog Glitch Impulse 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 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%. 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. A | 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. 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. 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. 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. 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.
Rev. A | Page 19 of 28
AD5678 THEORY OF OPERATION
D/A SECTION
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.
VDD REF (+) DAC REGISTER RESISTOR STRING REF (-)
OUTPUT AMPLIFIER (GAIN = +2)
R
R
R
TO OUTPUT AMPLIFIER
VOUT
R
05299-005
GND
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
D VOUT = VREFIN x N 2
the ideal output voltage when using an internal reference is given by
INTERNAL REFERENCE
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 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. Individual channel power-down is not supported while using the internal reference.
D VOUT = 2 x VREFOUT x 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.
RESISTOR STRING
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. A | Page 20 of 28
05299-006
R
AD5678
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 k 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/s with a 1/4 to 3/4 scale settling time of 10 s. Table 7. Command Definitions
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
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.
Table 8. Address Commands
A3 0 0 0 0 0 0 0 0 1 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
Rev. A | Page 21 of 28
AD5678
INPUT SHIFT REGISTER
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.
SYNC INTERRUPT
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 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
DB0 (LSB) X X
DATA BITS
COMMAND BITS
ADDRESS BITS
Figure 47. AD5678 Input Register Content for DAC A, B, G , H
DB31 (MSB) X 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 DB0 (LSB) X X
DATA BITS
COMMAND BITS
ADDRESS BITS
Figure 48. AD5678 Input Register Content for DAC C, D, E, F
SCLK
SYNC
DIN
DB31
DB0
DB31
DB0
05299-009
INVALID WRITE SEQUENCE: SYNC HIGH BEFORE 32ND FALLING EDGE
VALID WRITE SEQUENCE, OUTPUT UPDATES ON THE 32ND FALLING EDGE
Figure 49. SYNC Interrupt Facility
Rev. A | Page 22 of 28
05299-008
05299-007
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. the part is in power-down mode. There are three different options. The output is connected internally to GND through either a 1 k or a 100 k 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 s 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).
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.
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.
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
Rev. A | 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 0 1 1 DB8 0 1 0 1 Operating Mode Normal operation Power-down modes 1 k to GND 100 k 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 DB19 to DB10 X Don't cares
DB27 0
DB26 1
DB25 0
DB24 0
DB23 X
DB22 X
DB21 X
DB20 X
DB9 PD1
DB8 PD0
Command bits (C3 to C0)
Address bits (A3 to A0)-- don't cares
Powerdown mode
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 RESISTOR STRING DAC
VOUT
POWER-DOWN CIRCUITRY
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 DB19 to DB2 X Don't cares LSB DB1 DB0 CR1 CR0 Clear code register
Rev. A | Page 24 of 28
05299-010
RESISTOR NETWORK
AD5678
LDAC FUNCTION
The outputs of all DACs can be updated simultaneously using the hardware LDAC pin. 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. 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 Table 15. LDAC Register
Load DAC Register LDAC Bits (DB7 to DB0) LDAC Pin 0 1 1/0 X--don't care LDAC Operation Determined by LDAC pin DAC channels update, overriding the LDAC pin. DAC channels see LDAC as 0.
pin. See Table 16 for the contents of the input shift register during the load LDAC register mode of operation.
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 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. The power supply to the AD5678 should be bypassed with 10 F and 0.1 F capacitors. The capacitors should physically be as close as possible to the device, with the 0.1 F capacitor ideally right up against the device. The 10 F capacitors are the tantalum bead type. It is important that the 0.1 F 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 F 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.
Table 16. 32-Bit Input Shift Register Contents for LDAC Overwrite Function
MSB DB31 to DB28 X Don't cares LSB DB19 to DB8 X Don't cares
DB27 0
DB26 1
DB25 1
DB24 0
DB23 X
DB22 X
DB21 X
DB20 X
DB7 DAC H
DB6 DAC G
Command bits (C3 to C0)
Address bits (A3 to A0)-- don't cares
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
Rev. A | Page 25 of 28
AD5678 OUTLINE DIMENSIONS
5.10 5.00 4.90
14
8
4.50 4.40 4.30
1 7
6.40 BSC
PIN 1 1.05 1.00 0.80 0.65 BSC 1.20 MAX 0.15 0.05 0.30 0.19
0.20 0.09
SEATING COPLANARITY PLANE 0.10
8 0
0.75 0.60 0.45
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
1 8
6.40 BSC
PIN 1 0.15 0.05 0.65 BSC 0.30 0.19 COPLANARITY 0.10 1.20 MAX
0.20 0.09
SEATING PLANE
8 0
0.75 0.60 0.45
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 AD5678BRUZ-1 1 AD5678BRUZ-1REEL71 AD5678BRUZ-21 AD5678BRUZ-2REEL71 AD5678ARUZ-21 AD5678ARUZ-2REEL71
1
Temperature Range -40C to +105C -40C to +105C -40C to +105C -40C to +105C -40C to +105C -40C to +105C
Package Description 14-Lead TSSOP 14-Lead TSSOP 16-Lead TSSOP 16-Lead TSSOP 16-Lead TSSOP 16-Lead TSSOP
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
Z = Pb-free part.
Rev. A | Page 26 of 28
AD5678 NOTES
Rev. A | Page 27 of 28
AD5678 NOTES
(c) 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05299-0-11/05(A)
Rev. A | Page 28 of 28

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