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FEATURES Micropower--100 A Single-Supply-- 2.7 to 5.5 V Operation Compact 1.75 mm Height SO-8 Package & 1.1 mm Height TSSOP-8 AD7390--12-Bit Resolution AD7391--10-Bit Resolution SPI & QSPI Serial Interface Compatible with Schmitt Trigger Inputs APPLICATIONS Automotive 0.5 V to 4.5 V Output Span Voltage Portable Communications Digitally Controlled Calibration GENERAL DESCRIPTION
+3 Volt Serial-Input Micropower 10-Bit & 12-Bit DACs AD7390/AD7391
FUNCTIONAL DIAGRAM
AD7390
REF 12-BIT DAC 12 CLR LD EN CLK SDI 12 SERIAL REGISTER DAC REGISTER GND VDD VOUT
The AD7390/AD7391 family of 10-bit & 12-bit voltage-output digital-to-analog converters is designed to operate from a single 3 V supply. Built using a CBCMOS process, these monolithic DACs offer the user low cost, and ease-of-use in single-supply 3 V systems. Operation is guaranteed over the supply voltage range of 2.7 V to 5.5 V consuming less than 100 A making this device ideal for battery operated applications. The full-scale voltage output is determined by the external reference input voltage applied. The rail-to-rail REFIN to DACOUT allows for a full-scale voltage set equal to the positive supply VDD or any value in between.
A doubled-buffered serial-data interface offers high speed, three-wire, SPI and microcontroller compatible inputs using data in (SDI), clock (CLK) and load strobe (LD) pins. Additionally, a CLR input sets the output to zero scale at power on or upon user demand. Both parts are offered in the same pinout to allow users to select the amount of resolution appropriate for their application without circuit card redesign. The AD7390/AD7391 are specified over the extended industrial ( 40C to 85C) temperature range. The AD7391AR is specified for the 40C to 125C automotive temperature range. The AD7390/AD7391s are available in plastic DIP, and low profile 1.75 mm height SO-8 surface mount packages. The AD7391ARU is available for ultracompact applications in a thin 1.1 mm TSSOP-8 package.
1.00
2.0
AD7390
0.75 0.50 0.25
VDD = +3.0V
AD7390
1.5 1.0 0.5
INL - LSB
VDD = +3.0V VREF = +2.5V 25 , 85 C
DNL - LSB
0.00 0.25 0.50 0.75 1.00
0.0 0.5 1.0 1.5 2.0 55
TA = 55 C, 25 C, 85 C SUPERIMPOSED
0
512
1024
1536 2048 2560 CODE - Decimal
3072
3584
4096
0
512
1024
1536 2048 2560 CODE - Decimal
3072
2584
4096
Figure 1. Differential Nonlinearity Error vs. Code
Figure 2. INL Error vs. Code & Temperature
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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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. (c) Analog Devices, Inc., 1996 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
AD7390/AD7391-SPECIFICATIONS
AD7390 ELECTRICAL CHARACTERISTICS (@ V
Parameter STATIC PERFORMANCE Resolution1 Relative Accuracy2 Relative Accuracy2 Differential Nonlinearity2 Differential Nonlinearity2 Zero-Scale Error Full-Scale Voltage Error Full-Scale Voltage Error Full-Scale Tempco3 REFERENCE INPUT VREF IN Range Input Resistance Input Capacitance3 ANALOG OUTPUT Output Current (Source) Output Current (Sink) Capacitive Load3 LOGIC INPUTS Logic Input Low Voltage Logic Input High Voltage Input Leakage Current Input Capacitance3 INTERFACE TIMING3, 5 Clock Width High Clock Width Low Load Pulse Width Data Setup Data Hold Clear Pulse Width Load Setup Load Hold AC CHARACTERISTICS6 Output Slew Rate Settling Time DAC Glitch Digital Feedthrough Feedthrough SUPPLY CHARACTERISTICS Power Supply Range Positive Supply Current Positive Supply Current Power Dissipation Power Supply Sensitivity Symbol N INL INL DNL DNL VZSE VFSE VFSE TCVFS VREF RREF CREF IOUT IOUT CL VIL VIH IIL CIL tCH tCL tLDW tDS tDH tCLRW tLD1 tLD2 SR tS Q Q VOUT/VREF Data = 000H to FFFH to 000H To 0.1% of Full Scale Code 7FFH to 800H to 7FFH VREF = 1.5 VDC 1 V p-p, Data = 000H, f = 100 kHz DNL < 1 LSB VIL = 0 V, No Load, TA = VIL = 0 V, No Load VIL = 0 V, No Load VDD = 5% Data = 800H, VOUT = 5 LSB Data = 800H, VOUT = 5 LSB No Oscillation
REF IN
= 2.5 V,
40 C < TA <
85 C, unless otherwise noted)
3V 10% 5V 12 1.6 2 0.9 1 4.0 8 20 16 0/VDD 2.5 5 1 3 100 0.8 VDD 0.6 10 10 30 30 20 10 15 15 15 20 0.05 60 65 15 63 10% Units Bits LSB max LSB max LSB max LSB max mV max mV max mV max ppm/C typ V min/max M typ4 pF typ mA typ mA typ pF typ V max V min A max pF max ns min ns min ns min ns min ns min ns min ns min ns min V/s typ s typ nVs typ nVs typ dB typ
Conditions
12 TA = 25C 1.6 TA = 40C, 85C 2.0 TA = 25C, Monotonic 0.9 Monotonic 1 Data = 000H 4.0 TA = 25C, 85C, Data = FFFH 8 TA = 40C, Data = FFFH 20 16 0/VDD 2.5 5 1 3 100 0.5 VDD 0.6 10 10 50 50 30 10 30 15 30 40 0.05 70 65 15 63
VDD RANGE IDD IDD PDISS PSS
25C
2.7/5.5 55 100 300 0.003
2.7/5.5 55 100 500 0.006
V min/max A typ A max W max %/% max
NOTES 1 One LSB = VREF /4096 V for the 12-bit AD7390. 2 The first two codes (000 H, 001H) are excluded from the linearity error measurement. 3 These parameters are guaranteed by design and not subject to production testing. 4 Typicals represent average readings measured at 25C. 5 All input control signals are specified with tR = tF = 2 ns (10% to 90% of 3 V) and timed from a voltage level of 1.6 V. 6 The settling time specification does not apply for negative going transitions within the last 3 LSBs of ground. Specifications subject to change without notice.
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SPECIFICATIONS
AD7391 ELECTRICAL CHARACTERISTICS (@ V
Parameter STATIC PERFORMANCE Resolution1 Relative Accuracy2 Relative Accuracy2 Differential Nonlinearity2 Zero-Scale Error Full-Scale Voltage Error Full-Scale Voltage Error Full-Scale Tempco3 REFERENCE INPUT VREF IN Range Input Resistance Input Capacitance3 ANALOG OUTPUT Output Current (Source) Output Current (Sink) Capacitive Load3 LOGIC INPUTS Logic Input Low Voltage Logic Input High Voltage Input Leakage Current Input Capacitance3 INTERFACE TIMING3, 5 Clock Width High Clock Width Low Load Pulse Width Data Setup Data Hold Clear Pulse Width Load Setup Load Hold AC CHARACTERISTICS6 Output Slew Rate Settling Time DAC Glitch Digital Feedthrough Feedthrough SUPPLY CHARACTERISTICS Power Supply Range Positive Supply Current Positive Supply Current Power Dissipation Power Supply Sensitivity Symbol N INL INL DNL VZSE VFSE VFSE TCVFS VREF RREF CREF IOUT IOUT CL VIL VIH IIL CIL tCH tCL tLDW tDS tDH tCLRW tLD1 tLD2 SR tS Q Q VOUT/VREF Data = 000H to 3FFH to 000H To 0.1% of Full Scale Code 7FFH to 800H to 7FFH VREF = 1.5 VDC 1 V p-p, Data = 000H, f = 100 kHz DNL < 1 LSB VIL = 0 V, No Load, TA = VIL = 0 V, No Load VIL = 0 V, No Load VDD = 5% Data = 800H, VOUT = 5 LSB Data = 800H, VOUT = 5 LSB No Oscillation Conditions
REF IN
AD7390/AD7391
= 2.5 V, 40 C < TA < 85 C, unless otherwise noted)
3V 10 1.75 2.0 0.9 9.0 32 35 16 0/VDD 2.5 5 1 3 100 0.5 VDD 0.6 10 10 50 50 30 10 30 15 30 40 0.05 70 65 15 63 10% 5V 10 1.75 2.0 0.9 9.0 32 35 16 0/VDD 2.5 5 1 3 100 0.8 VDD 0.6 10 10 30 30 20 10 15 15 15 20 0.05 60 65 15 63 10% Units Bits LSB max LSB max LSB max mV max mV max mV max ppm/C typ V min/max M typ4 pF typ mA typ mA typ pF typ V min V max A max pF max ns ns ns ns ns ns ns ns V/s typ s typ nVs typ nVs typ dB typ
TA = 25C TA = 40C, 85C, 125C Monotonic Data = 000H TA = 25C, 85C, 125C, Data = 3FFH TA = 40C, Data = 3FFH
VDD RANGE IDD IDD PDISS PSS
25C
2.7/5.5 55 100 300 0.003
2.7/5.5 55 100 500 0.006
V min/max A typ A max W max %/% max
NOTES 1 One LSB = VREF /1024 V for the 10-bit AD7391. 2 The first two codes (000 H, 001H) are excluded from the linearity error measurement. 3 These parameters are guaranteed by design and not subject to production testing. 4 Typicals represent average readings measured at 25C. 5 All input control signals are specified with tR = tF = 2 ns (10% to 90% of 3 V) and timed from a voltage level of 1.6 V. 6 The settling time specification does not apply for negative going transitions within the last 3 LSBs of ground. Specifications subject to change without notice.
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AD7390/AD7391
ABSOLUTE MAXIMUM RATINGS* PIN CONFIGURATIONS SO-8 TSSOP-8
1 2 3 4 8 TOP VIEW (Not to Scale) 7 6 5 1 2 8
VDD to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 V, 8 V VREF to GND . . . . . . . . . . . . . . . . . . . . . . . 0.3 V, VDD 0.3 V Logic Inputs to GND . . . . . . . . . . . . . . . . . . . . . 0.3 V, 8 V VOUT to GND . . . . . . . . . . . . . . . . . . . . . 0.3 V, VDD 0.3 V IOUT Short Circuit to GND . . . . . . . . . . . . . . . . . . . . . . 50 mA Package Power Dissipation . . . . . . . . . . . . . . (TJ MAX TA)/JA Thermal Resistance JA 8-Pin Plastic DIP Package (N-8) . . . . . . . . . . . . . . 103C/W 8-Lead SOIC Package (SO-8) . . . . . . . . . . . . . . . . 158C/W TSSOP-8 Package (RU-8) . . . . . . . . . . . . . . . . . . . 240C/W Maximum Junction Temperature (TJ MAX) . . . . . . . . . . 150C Operating Temperature Range . . . . . . . . . . . 40C to 85C Storage Temperature Range . . . . . . . . . . . . 65C to 150C Lead Temperature (Soldering, 10 secs) . . . . . . . . . . . . 300C
NOTES *Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational specification is not implied. Exposure to the above maximum rating conditions for extended periods may affect device reliability.
7 TOP VIEW (Not to Scale) 6 3 4 5
P-DIP-8
LD CLK SDI CLR 1 2 3 4 TOP VIEW (Not to Scale) 8 7 6 5 VREF VDD VOUT GND
ORDERING GUIDE
PIN DESCRIPTIONS
Model AD7390AN AD7390AR AD7391AN AD7391AR AD7391ARU
Res 12 12 10 10 10
Temp XIND XIND XIND AUTO XIND
Package Description 8-Pin P-DIP 8-Lead SOIC 8-Pin P-DIP 8-Lead SOIC TSSOP-8
Package Option N-8 SO-8 N-8 SO-8 RU-8
Pin No. 1
Name LD
Function Load Strobe. Transfers shift register data to DAC register while active low. See truth table for operation. Clock Input. Positive edge clocks data into shift register. Serial Data Input. Data loads directly into the shift register. Resets DAC register to zero condition. Active low input. Analog & Digital Ground. DAC Voltage Output. Full-scale output 1 LSB less than reference input voltage REF. Positive Power Supply Input. Specified range of operation 2.7 V to 5.5 V. DAC Reference Input Pin. Establishes DAC full-scale voltage.
2 3 4 5 6
CLK SDI CLR GND VOUT VDD VREF
NOTES XIND = 40C to 85C; AUTO = 40C to 125C The AD7390 contains 558 transistors. The die size measures 70 mil X 68 mil.
CLR LD
RESET LOAD
DAC REGISTER
7
12
8
CLK CLK SDI D 12-BIT AD7390* SHIFT REGISTER
* NOTE: AD7391 HAS A 10-BIT SHIFT REGISTER
Figure 3. Digital Control Logic
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 the AD7390/AD7391 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.
WARNING!
ESD SENSITIVE DEVICE
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AD7390/AD7391
SDI
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
AD7390
CLK
AD7391 tLD2 tLD1
tLD1
LD DAC REGISTER LOAD
SDI
tDS
CLK
tDH tCH tLDW
tCL
LD
CLR
tS
FS VOUT ZS 0.1% FS ERROR BAND
tCLRW
tS
Figure 4. Timing Diagram
Table I. Control-Logic Truth Table
CLK X X X X
CLR H H L
LD H L X H L
Serial Shift Register Function Shift-Register-Data Advanced One-Bit Disables No Effect No Effect Disabled
DAC Register Function Latched Updated with Current Shift Register Contents Loaded with all Zeros Latched with all Zeros Previous SR Contents Loaded (Avoid usage of CLR when LD is logic low, since SR data could be corrupted if a clock edge takes place, while CLR returns high.)
NOTES 1 = Positive logic transition. 2 X = Don't care.
Table II. AD7390 Serial Input Register Data Format, Data is Loaded in the MSB-First Format
MSB B11 AD7390 D11 B10 D10 B9 D9 B8 D8 B7 D7 B6 D6 B5 D5 B4 D4 B3 D3 B2 D2 B1 D1
LSB B0 D0
Table III. AD7391 Serial Input Register Data Format, Data is Loaded in the MSB-First Format
MSB B9 AD7391 D9 B8 D8 B7 D7 B6 D6 B5 D5 B4 D4 B3 D3 B2 D2 B1 D1
LSB B0 D0
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AD7390/AD7391-Typical Performance Characteristics
25 100 30
AD7390
20 SS = 100 units TA = 25 C VDD = 2.7V VREF = 2.5V
90 80 70
AD7391
SS = 300 units TA = 25 C VDD = 2.7V VREF = 2.5V FREQUENCY 24
AD7391
SS = 100 units TA = 40 to 85 C VDD = 2.7V VREF = 2.5V
FREQUENCY
15
FREQUENCY
60 50 40 30
18
10
12
5
20 10
6
0
5.0 5.8 6.6 7.3 8.1 8.9 9.7 10.5 11.2 12.0 TOTAL UNADJUSTED ERROR - LSB
0
-10 -3.3 3.3 10 16 23 30 36 43 50 TOTAL UNADJUSTED ERROR - LSB
0
-33 -30 -26 -23 -20 -16 -13 -10 -6 -3 FULL SCALE TEMPCO - ppm/C
0
Figure 5. AD7390 Total Unadjusted Error Histogram
Figure 6. AD7391 Total Unadjusted Error Histogram
Figure 7. AD7391 Full-Scale Output Tempco Histogram
16
AD7390
OUTPUT VOLTAGE NOISE - V/Hz
100 95
SUPPLY CURRENT - A
5.0 VLOGIC FROM 3.0V TO 0V 4.5
THRESHOLD VOLTAGE - V
AD7390
CODE = FFFH VREF = 2V LOGIC VOLTAGE VARIED VLOGIC FROM HIGH TO LOW
14 12 10 8 6 4 2 0 1
VDD = 5V VREF = 2.5V TA = 25 C
90 85
VLOGIC FROM 0V TO 3.0V
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
AD7390
80 75 70 65 60 55 TA = 25 C VDD = 3.0V
VLOGIC FROM LOW TO HIGH
10
100 1K FREQUENCY - Hz
10K
100K
50 0.0
0.5
1.0
1.5 2.0 VIN - Volts
2.5
3.0
1
2
3 4 5 SUPPLY VOLTAGE - V
6
7
Figure 8. Voltage Noise Density vs. Frequency
Figure 9. Supply Current vs. Logic Input Voltage
Figure 10. Logic Threshold vs. Supply Voltage
100
1000
60
AD7390
90 SUPPLY CURRENT - A 80 70 60 50 40 30 20 0 1K VDD = 3.0V, VLOGIC = 0V SAMPLE SIZE = 300 UNITS SUPPLY CURRENT - A VDD = 5.0V, VLOGIC = 0V VDD = 3.6V, VLOGIC = 2.4V 800
AD7391
VLOGIC = 0V TO VDD TO 0V VREF = 2.5V TA = 25 C PSRR - dB 50 VDD = 5V 5%
TA = 25 C
40 600 a. VDD = 5.5V, CODE = 155H b. VDD = 5.5V, CODE = 3FFH c. VDD = 2.7V, CODE = 155H d. VDD = 2.7V, CODE = 355H ab VDD = 3V 30 5%
400
20
200 dc 10K 100K 1M CLOCK FREQUENCY - Hz 10M
10
55
35
15
5 25 45 65 85 105 125 TEMPERATURE - C
0 10
100 1K FREQUENCY - Hz
10K
Figure 11. Supply Current vs. Temperature
Figure 12. Supply Current vs. Clock Frequency
Figure 13. Power Supply Rejection vs. Frequency
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AD7390/AD7391
40
2s
VOUT (5mV/DIV)
AD7390
5s
VDD = 5V VREF = 2.5V
fCLK = 50KHz
VOUT (5mV/DIV) = HIGH
30 VDD = +5V VREF = +3V CODE = OOOH 20
IOUT - mA
10
(5V/DIV)
VDD = 5V VREF = 2.5V
20mV
fCLK = 50KHz CODE: 7FH to 80H
TIME - 2s/DIV
5mV
TIME - 5s/DIV
CLK (5V/DIV)
0
0
1
2 3 VOUT - V
4
5
Figure 14. IOUT at Zero Scale vs. VOUT
Figure 15. Midscale Transition Performance
Figure 16. Digital Feedthrough
5
100s
2.0 INTEGRAL NONLINEARITY - LSB 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
AD7390
0 5
AD7390
VDD = +5V CODE = 768H TA = 25 C
GAIN - dB
VOUT (1V/DIV) VDD = 5V VREF = 2.5V (5V/DIV)
10 15 20 25
VDD = +5V VREF = +100mV + 2VDC DATA = FFFH
fCLK = 50KHz
1V
TIME - 100s/div
30 10
100
1K 10K FREQUENCY - Hz
100K
0.0 0 1 2 3 4 REFERENCE VOLTAGE - V 5
Figure 17. Large Signal Settling Time
Figure 18. Reference Multiplying Bandwidth
Figure 19. INL Error vs. Reference Voltage
1.2 NOMINAL CHANGE IN VOLTAGE - mV
AD7390
SAMPLE SIZE = 50 1.0
0.8 CODE = FFFH 0.6
0.4 CODE = 000H
0.2
0.0
0
200 300 400 500 100 HOURS OF OPERATION AT 150C
600
Figure 20. Long-Term Drift Accelerated by Burn-In
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AD7390/AD7391
OPERATION
VDD P-CH
The AD7390 and AD7391 are a set of pin compatible, 12-bit/10bit digital-to-analog converters. These single-supply operation devices consume less than 100 microamps of current while operating from power supplies in the 2.7 V to 5.5 V range making them ideal for battery operated applications. They contain a voltage-switched, 12-bit/10-bit, laser-trimmed digital-toanalog converter, rail-to-rail output op amps, serial-input register, and a DAC register. The external reference input has constant input resistance independent of the digital code setting of the DAC. In addition, the reference input can be tied to the same supply voltage as VDD resulting in a maximum output voltage span of 0 to VDD . The SPI compatible, serial-data interface consists of a serial data input (SDI), clock (CLK), and load (LD) pins. A CLR pin is available to reset the DAC register to zero-scale. This function is useful for power-on reset or system failure recovery to a known state.
D/A CONVERTER SECTION
N-CH
VOUT
AGND
Figure 21. Equivalent Analog Output Circuit
The rail-to-rail output stage provides 1 mA of output current. The N-channel output pull-down MOSFET shown in Figure 21 has a 35 ON resistance, which sets the sink current capability near ground. In addition to resistive load driving capability, the amplifier has also been carefully designed and characterized for up to 100 pF capacitive load driving capability.
REFERENCE INPUT
The voltage switched R-2R DAC generates an output voltage dependent on the external reference voltage connected to the VREF pin according to the following equation: D Equation 1 2N where D is the decimal data word loaded into the DAC register, and N is the number of bits of DAC resolution. In the case of the 10-bit AD7391 using a 2.5 V reference, Equation 1 simplifies to: VOUT = VREF VOUT = 2.5 D 1024 Equation 2
Using Equation 2 the nominal midscale voltage at VOUT is 1.25 V for D = 512; full-scale voltage is 2.497 volts. The LSB step size is = 2.5 1/1024 = 0.0024 volts. For the 12-bit AD7390 operating from a 5.0 V reference Equation 1 becomes: VOUT = 5.0 D 4096 Equation 3
The reference input terminal has a constant input-resistance independent of digital code which results in reduced glitches on the external reference voltage source. The high 2 M inputresistance minimizes power dissipation within the AD7390/ AD7391 D/A converters. The VREF input accepts input voltages ranging from ground to the positive-supply voltage VDD . One of the simplest applications which saves an external reference voltage source is connection of the VREF terminal to the positive VDD supply. This connection results in a rail-to-rail voltage output span maximizing the programmed range. The reference input will accept ac signals as long as they are kept within the supply voltage range, 0 < VREF IN < VDD. The reference bandwidth and integral nonlinearity error performance are plotted in the typical performance section, see Figures 18 and 19. The ratiometric reference feature makes the AD7390/AD7391 an ideal companion to ratiometric analog-to-digital converters such as the AD7896.
POWER SUPPLY
Using Equation 3 the AD7390 provides a nominal midscale voltage of 2.5 V for D =2048, and a full-scale output of 4.998 V. The LSB step size is = 5.0 1/4096 = 0.0012 volts.
AMPLIFIER SECTION
The very low power consumption of the AD7390/AD7391 is a direct result of a circuit design optimizing the use of a CBCMOS process. By using the low power characteristics of CMOS for the logic, and the low noise, tight-matching of the complementary bipolar transistors, excellent analog accuracy is achieved. One advantage of the rail-to-rail output amplifiers used in the AD7390/ AD7391 is the wide range of usable supply voltage. The part is fully specified and tested for operation from 2.7 V to 5.5 V.
POWER SUPPLY BYPASSING AND GROUNDING
The internal DAC's output is buffered by a low power consumption precision amplifier. The op amp has a 60 s typical settling time to 0.1% of full scale. There are slight differences in settling time for negative slewing signals versus positive. Also, negative transition settling time to within the last 6 LSBs of zero volts has an extended settling time. The rail-to-rail output stage of this amplifier has been designed to provide precision performance while operating near either power supply. Figure 21 shows an equivalent output schematic of the rail-to-rail amplifier with its N-channel pull-down FETs that will pull an output load directly to GND. The output sourcing current is provided by a P-channel pull-up device that can source current to GND terminated loads.
Precision analog products, such as the AD7390/AD7391, require a well filtered power source. Since the AD7390/AD7391 operates from a single 3 V to 5 V supply, it seems convenient to simply tap into the digital logic power supply. Unfortunately, the logic supply is often a switch-mode design, which generates noise in the 20 kHz to 1 MHz range. In addition, fast logic gates can generate glitches hundred of millivolts in amplitude due to wiring resistance and inductance. The power supply noise generated thereby means that special care must be taken to assure that the inherent precision of the DAC is maintained. Good engineering judgment should be exercised when addressing the power supply grounding and bypassing of the AD7390.
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AD7390/AD7391
The AD7390 should be powered directly from the system power supply. This arrangement, shown in Figure 22, employs an LC filter and separate power and ground connections to isolate the analog section from the logic switching transients.
FERRITE BEAD: 2 TURNS, FAIR-RITE #2677006301 TTL/CMOS LOGIC CIRCUITS +5V 100F ELECT. 10-22F TANT. 0.1F CER. +5V RETURN VDD LOGIC IN GND
Figure 24. Equivalent Digital Input ESD Protection
+5V POWER SUPPLY
Figure 22. Use Separate Traces to Reduce Power Supply Noise
Whether or not a separate power supply trace is available, however, generous supply bypassing will reduce supply-line induced errors. Local supply bypassing consisting of a 10 F tantalum electrolytic in parallel with a 0.1 F ceramic capacitor is recommended in all applications (Figure 23).
+2.7V to +5.5V 0.1 F 10 F
In order to minimize power dissipation from input-logic levels that are near the VIH and VIL logic input voltage specifications, a Schmitt trigger design was used that minimizes the input-buffer current consumption compared to traditional CMOS input stages. Figure 9 shows a plot of incremental input voltage versus supply current showing that negligible current consumption takes place when logic levels are in their quiescent state. The normal crossover current still occurs during logic transitions. A secondary advantage of this Schmitt trigger, is the prevention of false triggers that would occur with slow moving logic transitions when a standard CMOS logic interface or opto isolators are used. The logic inputs SDI, CLK, LD, CLR all contain the Schmitt trigger circuits.
DIGITAL INTERFACE
*
C
8 REF 1 2 3 4
7 VDD
LD CLK SDI CLR
AD7390 or AD7391
GND 5
6
VOUT
* OPTIONAL EXTERNAL
REFERENCE BYPASS
Figure 23. Recommended Supply Bypassing for the AD7390/AD7391
INPUT LOGIC LEVELS
All digital inputs are protected with a Zener-type ESD protection structure (Figure 24) that allows logic input voltages to exceed the VDD supply voltage. This feature can be useful if the user is driving one or more of the digital inputs with a 5 V CMOS logic input-voltage level while operating the AD7390/ AD7391 on a 3 V power supply. If this mode of interface is used, make sure that the VOL of the 5 V CMOS meets the VIL input requirement of the AD7390/AD7391 operating at 3 V. See Figure 10 for a graph for digital logic input threshold versus operating VDD supply voltage.
The AD7390/AD7391 have a double-buffered serial data input. The serial-input register is separate from the DAC register, which allows preloading of a new data value into the serial register without disturbing the present DAC values. A functional block diagram of the digital section is shown in Figure 4, while Table I contains the truth table for the control logic inputs. Three pins control the serial data input. Data at the Serial Data Input (SDI) is clocked into the shift register on the rising edge of CLK. Data is entered in MSB-first format. Twelve clock pulses are required to load the 12-bit AD7390 DAC value. If additional bits are clocked into the shift register, for example when a microcontroller sends two 8-bit bytes, the MSBs are ignored (Figure 25). The CLK pin is only enabled when Load (LD) is high. The lower resolution 10-bit AD7391 contains a 10-bit shift register. The AD7391 is also loaded MSB first with 10 bits of data. Again if additional bits are clocked into the shift register, only the last 10 bits clocked in are used. The Load pin (LD) controls the flow of data from the shift register to the DAC register. After a new value is clocked into the serial-input register, it will be transferred to the DAC register by the negative transition of the Load pin (LD).
BYTE 1 MSB B15 X X B14 X X B13 X X B12 X X B11 D11 X B10 D!0 X B9 D9 D9 LSB B8 D8 D8 MSB B7 D7 D7 B6 D6 D6 B5 D5 D5
BYTE 0 LSB B4 D4 D4 B3 D3 D3 B2 D2 D2 B1 D1 D1 B0 D0 D0
D11_D0: 12-BIT AD7390 DAC VALUE; D9_D0 10-BIT AD7391 DAC VALUE X = DON'T CARE THE MSB OF BYTE 1 IS THE FIRST BIT THAT IS LOADED INTO THE DAC
Figure 25. Typical AD7390-Microprocessor Serial Data Input Forms
REV. 0
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AD7390/AD7391
RESET (CLR) PIN
Forcing the CLR pin low will set the DAC register to all zeros and the DAC output voltage will be zero volts. The reset function is useful for setting the DAC outputs to zero at power-up or after a power supply interruption. Test systems and motor controllers are two of many applications which benefit from powering up to a known state. The external reset pulse can be generated by the microprocessor's power-on RESET signal, by an output from the microprocessor, or by an external resistor and capacitor. CLR has a Schmitt trigger input which results in a clean reset function when using external resistor/capacitor generated pulses. The CLR input overrides other logic inputs, specifically LD. However, LD should be set high before CLR goes high. If CLR is kept low, then the contents of the shift register will be transferred to the DAC register as soon as CLR returns high. See the Control-Logic Truth Table I.
UNIPOLAR OUTPUT OPERATION
sumption OP196 has been designed just for this purpose and results in only 50 microamps of maximum current consumption. Connection of the equal valued 470 k resistors results in a differential amplifier mode of operation with a voltage gain of two, which results in a circuit output span of ten volts, that is, 5 V to 5 V. As the DAC is programmed with zero-code 000H to midscale 200H to full-scale 3FFH, the circuit output voltage VO is set at 5 V, 0 V and 5 V (minus 1 LSB). The output voltage VO is coded in offset binary according to Equation 4. VO = D 512 1 5 Equation 4
This is the basic mode of operation for the AD7390. As shown in Figure 26, the AD7390 has been designed to drive loads as low as 5 k in parallel with 100 pF. The code table for this operation is shown in Table IV.
+2.7V to +5.5V R 0.01F 7 EXT REF LD C RS SDI 3 1 GND 5 REF VDD 0.1F 10F
AD7390
VOUT 6
where D is the decimal code loaded in the AD7391 DAC register. Note that the LSB step size is 10/1024 = 10 mV. This circuit has been optimized for micropower consumption including the 470 k gain setting resistors, which should have low temperature coefficients to maintain accuracy and matching (preferably the same material, such as metal film). If better stability is required the power supply could be substituted with a precision reference voltage such as the low dropout REF195, which can easily supply the circuit's 162 A of current, and still provide additional power for the load connected to VO. The micropower REF195 is guaranteed to source 10 mA output drive current, but only consumes 50 A internally. If higher resolution is required, the AD7390 can be used with the addition of two more bits of data inserted into the software coding, which would result in a 2.5 mV LSB step size. Table V shows examples of nominal output voltages VO provided by the Bipolar Operation circuit application.
ISY < 162A
CLK 2 CLR 4
RL 5k
CL 100pF
5V 470k < 100A 470k < 50A 5V REF C VDD VOUT VO
Figure 26. AD7390 Unipolar Output Operation
Table IV. AD7390 Unipolar Code Table
OP196
5V
Hexadecimal Number in DAC Register FFF 801 800 7FF 000
Decimal Number in DAC Register 4095 2049 2048 2047 0
Output Voltage (V) VREF = 2.5 V 2.4994 1.2506 1.2500 1.2494 0
BIPOLAR OUTPUT SWING
AD7391
GND
5V
DIGITAL INTERFACE CIRCUITRY OMITTED FOR CLARITY
Figure 27. Bipolar Output Operation
Table V. Bipolar Code Table
The circuit can be configured with an external reference plus power supply, or powered from a single dedicated regulator or reference depending on the application performance requirements.
BIPOLAR OUTPUT OPERATION
Hexadecimal Number In DAC Register 3FF 201 200 1FF 000
Decimal Number in DAC Register 1023 513 512 511 0
Analog Output Voltage (V) 4.9902 0.0097 0.0000 -0.0097 -5.0000
Although the AD7391 has been designed for single-supply operation, the output can be easily configured for bipolar operation. A typical circuit is shown in Figure 27. This circuit uses a clean regulated 5 V supply for power, which also provides the circuit's reference voltage. Since the AD7391 output span swings from ground to very near 5 V, it is necessary to choose an external amplifier with a common-mode input voltage range that extends to its positive supply rail. The micropower con-
-10-
REV. 0
AD7390/AD7391
MICROCOMPUTER INTERFACES
The AD7390 serial data input provides an easy interface to a variety of single-chip microcomputers (Cs). Many Cs have a built-in serial data capability which can be used for communicating with the DAC. In cases where no serial port is provided, or it is being used for some other purpose (such as an RS-232 communications interface), the AD7390/AD7391 can easily be addressed in software. Twelve data bits are required to load a value into the AD7390. If more than 12 bits are transmitted before the load LD input goes high, the extra (i.e., the most-significant) bits are ignored. This feature is valuable because most Cs only transmit data in 8-bit increments. Thus, the C sends 16 bits to the DAC instead of 12 bits. The AD7390 will only respond to the last 12 bits clocked into the SDI input, however, so the serial-data interface is not affected. Ten data bits are required to load a value into the AD7391. If more than 10 bits are transmitted before load LD returns high, the extra bits are ignored.
REV. 0
-11-
AD7390/AD7391
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead SOIC (SO-8)
0.1968 (5.00) 0.1890 (4.80)
8 1 5 4
8-Pin Plastic DIP (N-8)
0.430 (10.92) 0.348 (8.84)
8 5
0.1574 (4.00) 0.1497 (3.80)
0.2440 (6.20) 0.2284 (5.80)
0.280 (7.11) 0.240 (6.10)
1 4
0.0098 (0.25) 0.0040 (0.10)
0.0196 (0.50) x 45 0.0099 (0.25)
0.210 (5.33) MAX 0.160 (4.06) 0.115 (2.93)
SEATING PLANE
0.0500 0.0192 (0.49) (1.27) 0.0138 (0.35) BSC
0.0098 (0.25) 0.0075 (0.19)
8 0
0.130 (3.30) MIN SEATING PLANE
0.195 (4.95) 0.115 (2.93)
0.0500 (1.27) 0.0160 (0.41)
0.022 (0.558) 0.100 0.070 (1.77) 0.014 (0.356) (2.54) 0.045 (1.15) BSC
0.015 (0.381) 0.008 (0.204)
8-Pin TSSOP (RU-8)
0.122 (3.10) 0.114 (2.90)
8
5
0.177 (4.50) 0.169 (4.30)
1
4
PIN 1 0.006 (0.15) 0.002 (0.05) 0.0256 (0.65) BSC 0.0433 (1.10) MAX 0.0118 (0.30) 0.0075 (0.19) 0.0079 (0.20) 0.0035 (0.090)
0.256 (6.50) 0.246 (6.25)
SEATING PLANE
8 0
0.028 (0.70) 0.020 (0.50)
-12-
REV. 0
PRINTED IN U.S.A.
C2151-18-7/96
PIN 1
0.0688 (1.75) 0.0532 (1.35)
PIN 1
0.060 (1.52) 0.015 (0.38)
0.325 (8.25) 0.300 (7.62)

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