AD7393

a FEATURES Micropower: 100 A 0.1 A Typical Power Shutdown Single-Supply +2.7 V to +5.5 V Operation Compact 1.1 mm Height TSSOP-20 Package AD7392/12-Bit Resolution AD7393/10-Bit Resolution 0.9 LSB Differential Nonlinearity Error APPLICATIONS Automotive 0.5 V to 4.5 V Output Span Voltage Portable Communications Digitally Controlled Calibration PC Peripherals GENERAL DESCRIPTION +3 V, Parallel Input Micropower 10- and 12-Bit DACs AD7392/AD7393 FUNCTIONAL BLOCK DIAGRAM AD7392 VREF 12-BIT DAC 12 DAC REGISTER 12 DGND CS DB0–DB11 RS VDD VOUT SHDN AGND The AD7392/AD7393 family of 10- and 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, 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. The voltage outputs are capable of sourcing 5 mA. A 12-bit wide data latch loads with a 45 ns write time allowing interface to the fastest processors without wait states. 1 Additionally, an asynchronous RS 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 applications without circuit card changes. The AD7392/AD7393 are specified for operation over the extended industrial (–40° C to +85°C) temperature range. The AD7393AR is specified for the –40°C to +125°C automotive temperature range. AD7392/AD7393s are available in plastic DIP, and 20-lead SOIC packages. The AD7393ARU is available for ultracompact applications in a thin 1.1 mm height TSSOP-20 package. For serial data input, 8-lead packaged versions, see the AD7390 and AD7391 products. 1 AD7392 0.8 0.6 0.4 VDD = +2.7V VREF = +2.5V TA = 25 C AD7393 0.8 0.6 0.4 DNL – LSB 0.2 0 0.2 0.4 0.6 0.8 1 0 128 256 384 512 640 CODE – Decimal VDD = +2.7V VREF = +2.5V TA = 25 C DNL – LSB 0.2 0 0.2 0.4 0.6 0.8 1 0 512 1024 1536 2048 2560 CODE – Decimal 3072 3584 4096 768 896 1024 Figure 1. AD7392 Differential Nonlinearity Error vs. Code Figure 2. AD7393 Differential Nonlinearity Error vs. Code R EV. 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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 1999 AD7392/AD7393–SPECIFICATIONS AD7392 ELECTRICAL CHARACTERISTICS (@ V Parameter STATIC PERFORMANCE Resolution1 Relative Accuracy2 Differential Nonlinearity2 Zero-Scale Error Full-Scale Voltage Error Full-Scale Tempco3 REFERENCE INPUT VREF IN Range Input Resistance Input Capacitance3 ANALOG 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 Chip Select Write Width Data Setup Data Hold Reset Pulsewidth AC CHARACTERISTICS Output Slew Rate Settling Time6 Shutdown Recovery Time DAC Glitch Digital Feedthrough Feedthrough SUPPLY CHARACTERISTICS Power Supply Range Positive Supply Current Shutdown Supply Current Power Dissipation Power Supply Sensitivity Symbol N INL DNL VZSE VFSE TCVFS VREF RREF CREF IOUT IOUT CL VIL VIH IIL CIL tCS tDS tDH tRS SR tS tSDR 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 V dc +1 V p-p, Data = 000H, f = 100 kHz DNL < 1 LSB VIL = 0 V, No Load SHDN = 0, 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 1.8 3 0.9 1 4.0 8.0 8 20 28 0/VDD 2.5 5 1 3 100 0.8 VDD 0.6 10 10 45 15 5 30 0.05 60 80 65 15 –63 2.7/5.5 55/100 0.1/1.5 500 0.006 10% Units Bits LSB max LSB max LSB max LSB max mV max mV max mV max mV max ppm/°C typ V min/max MΩ typ4 pF typ mA typ mA typ pF typ V max V min µA max pF max ns min ns min ns min ns min V/µs typ µs typ µs typ nV/s typ nV/s typ dB typ V min/max µA typ/max µA typ/max µW max %/% max Conditions 12 TA = 25°C 1.8 3 TA = 40°C, 85°C TA = 25°C, Monotonic 0.9 Monotonic 1 Data = 000H, TA = 25°C, 85°C 4.0 8.0 Data = 000H, TA = –40°C TA = 25°C, 85°C, Data = FFFH 8 20 TA = 40°C, Data = FFFH 28 0/VDD 2.5 5 1 3 100 0.5 VDD 0.6 10 10 45 30 20 40 0.05 70 65 15 –63 2.7/5.5 55/100 0.1/1.5 300 0.006 VDD RANGE IDD IDD–SD PDISS PSS NOTES 1 One LSB = VREF /4096 V for the 12-bit AD7392. 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 +25 °C. 5 All input control signals are specified with tR = tF = 2 ns (10% to 90% of 13 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. – 2– REV. A AD7392/AD7393 AD7393 ELECTRICAL CHARACTERISTICS (@ V Parameter STATIC PERFORMANCE Resolution1 Relative Accuracy2 Differential Nonlinearity2 Zero-Scale 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 Chip Select Write Width Data Setup Data Hold Reset Pulsewidth AC CHARACTERISTICS Output Slew Rate Settling Time6 Shutdown Recovery Time DAC Glitch Digital Feedthrough Feedthrough SUPPLY CHARACTERISTICS Power Supply Range Positive Supply Current Shutdown Supply Current Power Dissipation Power Supply Sensitivity Symbol N INL DNL VZSE VFSE TCVFS VREF RREF CREF IOUT IOUT CL VIL VIH IIL CIL tCS tDS tDH tRS SR tS tSDR 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 V dc 1 V p-p, Data = 000H, f = 100 kHz DNL < 1 LSB VIL = 0 V, No Load, TA = 25°C VIL = 0 V, No Load SHDN = 0, VIL = 0 V, No Load VIL = 0 V, No Load ∆VDD = 5% Data = 200H, ∆VOUT = 5 LSB Data = 200H, ∆VOUT = 5 LSB No Oscillation Conditions REF IN = 2.5 V, 40 C < T A < 85 C, unless otherwise noted) 3V 10 1.75 2.0 0.8 9.0 32 42 28 0/VDD 2.5 5 1 3 100 0.5 VDD 0.6 10 10 45 30 20 40 0.05 70 65 15 –63 2.7/5.5 55 100 0.1/1.5 300 0.006 10% 5V 10 1.75 2.0 0.8 9.0 32 42 28 0/VDD 2.5 5 1 3 100 0.8 VDD 0.6 10 10 45 15 5 30 0.05 60 80 65 15 –63 2.7/5.5 55 100 0.1/1.5 500 0.006 10% Units Bits LSB max LSB max LSB max mV max mV max mV max ppm/° C typ V min/max MΩ typ4 pF typ mA typ mA typ pF typ V max V min µA max pF max ns ns ns ns V/µs typ µs typ µs typ nV/s typ nV/s typ dB typ V min/max µA typ µA max µA typ/max µW max %/% max TA = 25°C TA = 40°C, 85°C, 125°C Monotonic Data = 000H TA = 25°C, 85°C, 125°C, Data = 3FFH TA = 40°C, Data = 3FFH VDD RANGE IDD IDD–SD PDISS PSS NOTES 1 One LSB = VREF /1024 V for the 10-bit AD7393. 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 +25 °C. 5 All input control signals are specified with t R = 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. REV. A – 3– AD7392/AD7393 ABSOLUTE MAXIMUM RATINGS* PIN CONFIGURATIONS VDD 1 SHDN 2 CS 3 RS 4 D0 5 D1 6 20 VREF 19 VOUT 18 AGND 17 DGND VDD 1 SHDN 2 CS 3 RS 4 NC 5 NC 6 20 VREF 19 VOUT 18 AGND 17 DGND VDD to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V, +8 V VREF to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V, VDD 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 DGND to AGND . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V, +2 V Package Power Dissipation . . . . . . . . . . . . . (TJ max – TA)/θJA Thermal Resistance θJA 20-Lead Plastic DIP Package (N-20) . . . . . . . . . . . 57°C/W 20-Lead SOIC Package (R-20) . . . . . . . . . . . . . . . . 60°C/W 20-Lead Thin-Shrink Surface Mount (RU-20) . . . 155°C/W Maximum Junction Temperature (TJ max) . . . . . . . . . . 150°C Operating Temperature Range . . . . . . . . . . . –40°C to +85°C AD7393AR . . . . . . . . . . . . . . . . . . . . . . . . . –40°C to +125°C Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C Lead Temperature N-20 (Soldering, 10 sec) . . . . . . . . . . . . . . . . . . . . . +300°C R-20 (Vapor Phase, 60 sec) . . . . . . . . . . . . . . . . . . .+215°C RU-20 (Infrared, 15 sec) . . . . . . . . . . . . . . . . . . . . . +220°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 sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 1 CS 0 AD7392 16 D11 AD7393 16 D9 TOP VIEW 15 D10 (Not to Scale) D2 7 14 D9 D3 8 D4 9 D5 10 13 D8 12 D7 11 D6 TOP VIEW 15 D8 (Not to Scale) D0 7 14 D7 D1 8 D2 9 D3 10 13 D6 12 D5 11 D4 NC = NO CONNECT PIN DESCRIPTION # 1 Name VDD Function tCS tDS 1 DB11–DB0 0 1 RS 0 FS VOUT ZS tDH DATA VALID tRS 0.1% FS ERROR BAND tS tS Positive Power Supply Input. Specified range of operation +2.7 V to +5.5 V. 2 SHDN Power Shutdown active low input. DAC register contents are saved as long as power stays on the VDD pin. When SHDN = 0, CS strobes will write new data into the DAC register. 3 CS Chip Select latch enable, active low. 4 RS Resets DAC register to zero condition. Asynchronous active low input. 5, 6 NC No connect Pins 5 and 6 on the AD7393. 17 DGND Digital Ground. 18 AGND Analog Ground. 19 VOUT DAC Voltage Output. 20 VREFIN DAC Reference Input Pin. Establishes DAC full-scale voltage. D0–D11 12 parallel input data bits. D11 = MSB Pin 16, D0 = LSB Pin 5, AD7392. D0–D9 10 parallel input data bits. D9 = MSB. Pin 16, D0 = LSB Pin 7, AD7393. ORDERING GUIDE Figure 3. Timing Diagram 1 OF 12 LATCHES OF THE DAC REGISTER Model TO INTERNAL DAC SWITCHES Res (LSB) 12 12 10 10 10 Temp XIND XIND XIND AUTO XIND Package Description 20-Lead P-DIP 20-Lead SOIC 20-Lead P-DIP 20-Lead SOIC TSSOP-20 Package Option N-20 R-20 N-20 R-20 RU-20 DBX CS RS AD7392AN AD7392AR AD7393AN AD7393AR AD7393ARU Figure 4. Digital Control Logic NOTES XIND = –40 °C to +85°C; AUTO = –40 °C to +125 °C. The AD7392 contains 709 transistors. The die size measures 78 mil × 85 mil = 6630 sq. mil. 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 AD7392/AD7393 feature 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 –4– REV. A Typical Performance Characteristics–AD7392/AD7393 1 0.8 0.6 0.4 INL – LSB INL – LSB 0.2 0 –0.2 –0.4 –0.6 –0.8 –1 0 512 1024 1536 2048 2560 3072 3584 4096 CODE – Decimal 1 AD7392 VDD = 2.7V VREF = 2.5V TA = 25 C 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1 0 AD7393 25 AD7392 FREQUENCY VDD = 2.7V VREF = 2.5V TA = 25 C 128 256 384 512 640 768 896 1024 CODE – Decimal SS = 100 UNITS TA = 25 C 20 VDD = 2.7V VREF = 2.5V 15 10 5 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 Figure 5. AD7392 Integral Nonlinearity Error vs. Code Figure 6. AD7393 Integral Nonlinearity Error vs. Code Figure 7. AD7392 Total Unadjusted Error Histogram 100 90 80 70 FREQUENCY 60 50 40 30 20 10 0 AD7393 SS = 300 UNITS TA = 25 C VDD = 2.7V VREF = 2.5V FREQUENCY 30 16 AD7393 OUTPUT VOLTAGE NOISE – V/ Hz 14 12 10 8 6 4 2 0 –66 –60 –52 –46 –40 –32 –26 –20 –12 –6 FULL SCALE TEMPCO – ppm/ C 0 AD7392 VDD = 5V VREF = 2.5V TA = 25 C SS = 100 UNITS TA = 40 to 85 C 24 VDD = 2.7V VREF = 2.5V 18 12 6 –10 –3.3 3.3 10 16 23 30 36 43 50 TOTAL UNADJUSTED ERROR – LSB 0 1 10 100 1k FREQUENCY – Hz 10k 100k Figure 8. AD7393 Total Unadjusted Error Histogram Figure 9. AD7393 Full-Scale Output Tempco Histogram Figure 10. Voltage Noise Density vs. Frequency 100 95 A 90 85 80 75 70 65 60 55 AD7392 THRESHOLD VOLTAGE – V TA = 25 C VDD = 3.0V VLOGIC FROM 0V TO 3.0V 5.0 4.5 4.0 3.5 3.0 100 AD7392 CODE = FFFH VREF = 2V RS LOGIC VOLTAGE VARIED 90 A 80 70 60 50 AD7392 SAMPLE SIZE = 300 UNITS VDD = 5.0V, VLOGIC = 0V VDD = 3.6V, VLOGIC = 2.4V SUPPLY CURRENT – VLOGIC FROM 3.0V TO 0V VLOGIC FROM 2.5 HIGH TO LOW 2.0 1.5 1.0 0.5 VLOGIC FROM LOW TO HIGH SUPPLY CURRENT – VDD = 3.0V, VLOGIC = 0V 40 30 20 50 0.0 0.5 1.0 1.5 2.0 VIN – Volts 2.5 3.0 0.0 1 2 3 4 5 SUPPLY VOLTAGE – V 6 7 55 35 15 5 25 45 65 85 105 125 TEMPERATURE – C Figure 11. Supply Current vs. Logic Input Voltage Figure 12. Logic Threshold vs. Supply Voltage Figure 13. Supply Current vs. Temperature REV. A –5– AD7392/AD7393 1000 AD7393 VLOGIC = 0V TO VDD TO 0V VREF = 2.5V TA = 25 C 60 40 VDD = 5V 5% TA = 25 C A 800 50 30 40 a b c PSRR – dB VDD = +5V VREF = +3V CODE = ØØØH 20 SUPPLY CURRENT – 400 a. VDD = 5.5V, CODE = 155H b. VDD = 5.5V, CODE = 3FFH c. VDD = 2.7V, CODE = 155H d. VDD = 2.7V, CODE = 355H VDD = 3V 30 5% 20 10 200 10 d 0 1k 100k 1M 10k CLOCK FREQUENCY – Hz 10M 0 10 0 1k 100 FREQUENCY – Hz 10k 0 1 2 3 VOUT – V 4 5 Figure 14. Supply Current vs. Clock Frequency Figure 15. Power Supply Rejection vs. Frequency Figure 16. IOUT at Zero Scale vs. VOUT IOUT – mA 600 TIME – 2 s/DIV TIME – 5 s/DIV TIME – 100 s/DIV Figure 17. Midscale Transition Performance Figure 18. Digital Feedthrough Figure 19. Large Signal Settling Time 5 0 5 GAIN – dB 10 15 20 25 30 10 VDD = +5V VREF = +100mV + 2VDC DATA = FFFH INTEGRAL NONLINEARITY – LSB 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 100 1k 10k FREQUENCY – Hz 100k 0.0 0 1.2 NOMINAL CHANGE IN VOLTAGE – mV AD7392 VDD = +5V CODE = 768H TA = 25 C AD7392 SAMPLE SIZE = 50 1.0 0.8 CODE = FFFH 0.6 0.4 CODE = 000H 0.2 1 2 3 4 REFERENCE VOLTAGE – V 5 0.0 0 200 300 400 500 100 HOURS OF OPERATION AT 150 C 600 Figure 20. Reference Multiplying Bandwidth Figure 21. INL Error vs. Reference Voltage Figure 22. Long-Term Drift Accelerated by Burn-in –6– REV. A AD7392/AD7393 1000 AD7392 100 100 IDD ( A) 50 0 2 VOUT (V) 0 1 0 90 SUPPLY CURRENT – nA 100 10 0% SHDN VDD = 5.5V VREF = 2.5V SHDN = 0V TIME – 100 s/DIV 10 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE – C Figure 23. Shutdown Recovery Time Figure 24. Shutdown Current vs. Temperature Table I. Control Logic Truth Table CS H L ↑ X H RS H H H L ↑ DAC Register Function Latched Transparent Latched with New Data Loaded with All Zeros Latched all Zeros NOTE ↑ Positive logic transition; X Don’t Care. OPERATION D/A CONVERTER SECTION The AD7392 and AD7393 comprise a set of pin compatible, 12-bit/10-bit 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 digitalto-analog converter, rail-to-rail output op amps, and a parallelinput 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 parallel data interface consists of 12 data bits, DB0–DB11, for the AD7392; 10 data bits, DB0–DB9, for the AD7393; and a CS write strobe. A RS 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. Additional power savings are accomplished by activating the SHDN pin, resulting in a 1.5 µA maximum consumption sleep mode. As long as the supply voltage remains, data will be retained in the DAC register to reset the DAC output when the part is taken out of shutdown (SHDN = 1). The voltage switched R-2R DAC generates an output voltage dependent on the external reference voltage connected to the REF pin according to the following equation: V OUT = V REF × D 2N Equation 1 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 AD7393 using a 2.5 V reference, Equation 1 simplifies to: V OUT = 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 AD7392 operating from a 5.0 V reference Equation 1 becomes: V OUT = V REF × D 2N Equation 3 Using Equation 3, the AD7392 provides a nominal midscale voltage of 2.50 V for D = 2048, and a full-scale output of 4.998 volts. The LSB step size is = 5.0 × 1/4096 = 0.0012 volts. REV. A –7– AD7392/AD7393 AMPLIFIER SECTION 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 µs 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 25 shows an equivalent output schematic of the rail-to-railamplifier 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. VDD P-CH Precision analog products, such as the AD7392/AD7393, require a well filtered power source. Since the AD7392/AD7393 operate 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 of hundreds of millivolts in amplitude due to wiring resistance and inductance. The power supply noise generated as a result 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 AD7392. The AD7392 should be powered directly from the system power supply. This arrangement, shown in Figure 26, 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 N-CH VOUT AGND TTL/CMOS LOGIC CIRCUITS +5V 100 F ELECT. 10-22 F TANT. 0.1 F CER. +5V RETURN Figure 25. 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 25, has a 35 Ω ON resistance that sets the sink current capability near ground. In addition to resistive load driving capability, the amplifier also has been carefully designed and characterized for up to 100 pF capacitive load driving capability. REFERENCE INPUT +5V POWER SUPPLY Figure 26. Use Separate Traces to Reduce Power Supply Noise 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 2.5 MΩ input-resistance minimizes power dissipation within the AD7392/AD7393 D/A converters. The VREF input accepts input voltages ranging from ground to the positive-supply voltage VDD. One of the simplest applications that saves an external reference voltage source is connection of the REF 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 20 and 21). The ratiometric reference feature makes the AD7392/ AD7393 an ideal companion to ratiometric analog-to-digital converters such as the AD7896. POWER SUPPLY Whether or not a separate power supply trace is available, generous supply bypassing will reduce supply line induced errors. Local supply bypassing, consisting of a 10 µF tantalum electrolytic in parallel with a 0.1 µF ceramic capacitor, is recommended in all applications (Figure 27). +2.7V TO +5.5V 20 REF 1 VDD 0.1 F 10 F 2 3 4 GND 17, 18 * DB0–DB11 SHDN CS RS C AD7392 OR AD7393 19 VOUT * OPTIONAL EXTERNAL REFERENCE BYPASS The very low power consumption of the AD7392/AD7393 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 AD7392/AD7393 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. Figure 27. Recommended Supply Bypassing for the AD7392/AD7393 –8– REV. A AD7392/AD7393 INPUT LOGIC LEVELS All digital inputs are protected with a Zener-type ESD protection structure (Figure 28) 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 AD7392/ AD7393 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 AD7392/AD7393 operating at 3 V. See Figure 12 for a graph for digital logic input threshold versus operating VDD supply voltage. VDD LOGIC IN GND 1k RESET (RS) PIN Forcing the asynchronous RS 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 that 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. RESET has a Schmitt trigger input which results in a clean reset function when using external resistor/capacitor generated pulses. See the Control-Logic Truth Table I. POWER SHUTDOWN (SHDN) Figure 28. Equivalent Digital Input ESD Protection 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 11 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 cross over 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 optoisolators are used. The logic inputs DB11–DB0, CS, RS, SHDN all contain the Schmitt trigger circuits. DIGITAL INTERFACE The AD7392/AD7393 have a parallel data input. A functional block diagram of the digital section is shown in Figure 4, while Table I contains the truth table for the logic control inputs. The chip select (CS) pin controls loading of data from the data inputs on pins DB11–DB0. This active low input places the input register into a transparent state allowing the data inputs to directly change the DAC ladder values. When CS returns to logic high within the data setup and hold time specifications, the new value of data in the input-register will be latched. See Truth Table for complete set of conditions. Maximum power savings can be achieved by using the power shutdown control function. This hardware activated feature is controlled by the active low input SHDN pin. This pin has a Schmitt trigger input that helps desensitize it to slowly changing inputs. By placing a logic low on this pin, the internal consumption of the AD7392 or AD7393 is reduced to nanoamp levels, guaranteed to 1.5 µA maximum over the operating temperature range. If power is present at all times on the VDD pin while in the shutdown mode, the internal DAC register will retain the last programmed data value. The digital interface is still active in shutdown, so that code changes can be made that will produce new DAC settings when the device is taken out of shutdown. This data will be used when the part is returned to the normal active state by placing the DAC back to its programmed voltage setting. Figure 23 shows a plot of shutdown recovery time with both IDD and VOUT displayed. In the shutdown state the DAC output amplifier exhibits an open-circuit high resistance state. Any load connected will stabilize at its termination voltage. If the power shutdown feature is not needed, the user should tie the SHDN pin to the VDD voltage thereby disabling this function. REV. A –9– AD7392/AD7393 UNIPOLAR OUTPUT OPERATION This is the basic mode of operation for the AD7392. As shown in Figure 29, the AD7392 has been designed to drive loads as low as 5 kΩ in parallel with 100 pF. The code table for this operation is shown in Table II. +2.7V TO +5.5V R 0.01 F 1 VDD 0.1 F 10 F 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.  D VO =  –1 ×5 512    Equation 4 AD7392 EXT REF DIGITAL INTERFACE CIRCUITRY OMITTED FOR CLARITY 20 REF VOUT 19 RL 5k CL 100pF AGND/DGND 17, 18 Figure 29. AD7392 Unipolar Output Operation Table II. Unipolar Code Table 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 where D is the decimal code loaded in the AD7393 DAC register. Note that the LSB step size is 10/1024 = 10 mV. This circuit has been optimized for micropower consumption including the 470 kΩ gain setting resistors, which should have low temperature coefficients to maintain accuracy and matching (preferably the same resistor 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 drop out REF195, which can easily supply the circuit’s 162 µA 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 µA internally. If higher resolution is required, the AD7392 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 III shows examples of nominal output voltages VO provided by the Bipolar Operation circuit application. ISY < 162 A +5V 470k