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| a FEATURES Voltage Options 2.048 V, 2.500 V and 4.096 V 2.7 V to 15 V Supply Range Supply Current 12 A max Initial Accuracy 2 mV max Temperature Coefficient 8 ppm/ C max Low-Noise 6 V p-p (0.1 Hz-10 Hz) High Output Current 5 mA min Temperature Range 40 C to 125 C REF02/REF19x Pinout APPLICATIONS Portable Instrumentation Precision Reference for 3 V and 5 V Systems A/D and D/A Converter Reference Solar Powered Applications Loop-Current Powered Instruments GENERAL DESCRIPTION Low Noise Micropower Precision Voltage References ADR290/ADR291/ADR292 PIN CONFIGURATIONS 8-Lead Narrow Body SO (R Suffix) 1 VIN 2 8 7 TOP VIEW (Not to Scale) 6 VOUT 3 5 ADR29x GND 4 8-Lead TSSOP (RU Suffix) 1 VIN 2 8 7 TOP VIEW 3 (Not to Scale) 6 VOUT 5 ADR29x GND 4 The ADR290, ADR291 and ADR292 are low noise, micropower precision voltage references that use an XFETTM reference circuit. The new XFET architecture offers significant performance improvements over traditional bandgap and Zener-based references. Improvements include: one quarter the voltage noise output of bandgap references operating at the same current, very low and ultralinear temperature drift, low thermal hysteresis and excellent long-term stability. The ADR29x family are series voltage references providing stable and accurate output voltages from supplies as low as 2.7 V. Output voltage options are 2.048 V, 2.5 V and 4.096 V for the ADR290, ADR291 and ADR292 respectively. Quiescent current is only 12 A, making these devices ideal for battery powered instrumentation. Three electrical grades are available offering initial output accuracies of 2 mV, 3 mV and 6 mV max for the ADR290 and ADR291 and 3 mV, 4 mV and 6 mV max for the ADR292. Temperature coefficients for the three grades are 8 ppm/C, 15 ppm/C and 25 ppm/C max, respectively. Line regulation and load regulation are typically 30 ppm/V and 30 ppm/mA, maintaining the reference's overall high performance. For a device with 5.0 V output, refer to the ADR293 data sheet. The ADR290, ADR291 and ADR292 references are specified over the extended industrial temperature range of -40C to +125C. Devices are available in the 8-lead SOIC, 8-lead TSSOP and the TO-92 package. 3-Pin TO-92 (T9 Suffix) PIN 1 PIN 2 PIN 3 VIN GND VOUT BOTTOM VIEW Part Number ADR290 ADR291 ADR292 Nominal Output Voltage (V) 2.048 2.500 4.096 XFET is a trademark of Analog Devices, Inc. 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 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: 617/329-4700 World Wide Web Site: http://www.analog.com Fax: 617/326-8703 (c) Analog Devices, Inc., 2000 ADR290/ADR291/ADR292 ADR290-SPECIFICATIONS Electrical Specifications (V = S 2.7 V, TA = 25 C unless otherwise noted) Conditions IOUT = 0 mA Min 2.046 2.045 2.042 Typ Max Units V V V ppm/V ppm/V ppm/mA ppm/mA ppm V p-p nV/Hz Parameter INITIAL ACCURACY "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade LONG TERM STABILITY NOISE VOLTAGE WIDEBAND NOISE DENSITY S Symbol VO 2.048 2.050 2.051 2.054 30 40 30 40 0.2 6 420 100 125 100 125 VO/VIN 2.7 V to 15 V, IOUT = 0 mA VO/ ILOAD VO eN en VS = 5.0 V, 0 mA to 5 mA 1000 hrs @ +25C, VS = +15 V 0.1 Hz to 10 Hz at 1 kHz Electrical Specifications (V = Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade S 2.7 V, TA = 25 C TA 85 C unless otherwise noted) Min Typ 3 6 10 35 50 20 30 Max 8 15 25 125 150 125 150 Units ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA Symbol TCVO/C Conditions IOUT = 0 mA VO/VIN 2.7 V to 15 V, IOUT = 0 mA VO/ ILOAD VS = 5.0 V, 0 mA to 5 mA Electrical Specifications (V = Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade SUPPLY CURRENT THERMAL HYSTERESIS NOTE Specifications subject to change without notice. 2.7 V, TA = 40 C TA 125 C unless otherwise noted) Min Typ 3 5 10 40 70 20 30 8 12 50 Max 10 20 30 200 250 200 300 12 15 Units ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA A A ppm Symbol TCVO/C Conditions IOUT = 0 mA VO/VIN 2.7 V to 15 V, IOUT = 0 mA VO/ ILOAD VS = 5.0 V, 0 mA to 5 mA @ +25C TO-92, SO-8, TSSOP-8 -2- REV. A ADR291-SPECIFICATIONS Electrical Specifications (V = S ADR290/ADR291/ADR292 25 C unless otherwise noted) Conditions IOUT = 0 mA Min 2.498 2.497 2.494 Typ Max Units V V V ppm/V ppm/V ppm/mA ppm/mA ppm V p-p nV/Hz 3.0 V, TA = Parameter INITIAL ACCURACY "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade LONG TERM STABILITY NOISE VOLTAGE WIDEBAND NOISE DENSITY S Symbol VO 2.500 2.502 2.503 2.506 30 40 30 40 0.2 8 480 100 125 100 125 VO/VIN 3.0 V to 15 V, IOUT = 0 mA VO/ ILOAD VO eN en VS = 5.0 V, 0 mA to 5 mA 1000 hrs @ +25C, VS = +15 V 0.1 Hz to 10 Hz at 1 kHz Electrical Specifications (V = Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade S 3.0 V, TA = 25 C T A 85 C unless otherwise noted) Min Typ 3 5 10 35 50 20 30 Max 8 15 25 125 150 125 150 Units ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA Symbol TCVO/C Conditions IOUT = 0 mA VO/VIN 3.0 V to 15 V, IOUT = 0 mA VO/ ILOAD VS = 5.0 V, 0 mA to 5 mA Electrical Specifications (V = Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade SUPPLY CURRENT THERMAL HYSTERESIS NOTE Specifications subject to change without notice. 3.0 V, TA = 40 C T A 125 C unless otherwise noted) Min Typ 3 5 10 40 70 20 30 9 12 50 Max 10 20 30 200 250 200 300 12 15 Units ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA A A ppm Symbol TCVO/C Conditions IOUT = 0 mA VO/VIN 3.0 V to 15 V, IOUT = 0 mA VO/ ILOAD VS = 5.0 V, 0 mA to 5 mA @ +25C TO-92, SO-8, TSSOP-8 REV. A -3- ADR290/ADR291/ADR292 ADR292-SPECIFICATIONS Electrical Specifications Parameter INITIAL ACCURACY "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade LONG TERM STABILITY NOISE VOLTAGE WIDEBAND NOISE DENSITY (VS = 5 V, T A = 25 C unless otherwise noted) Conditions IOUT = 0 mA Min 4.093 4.092 4.090 Typ Max Units V V V ppm/V ppm/V ppm/mA ppm/mA ppm V p-p nV/Hz Symbol VO 4.096 4.099 4.100 4.102 30 40 30 40 0.2 12 640 100 125 100 125 VO/VIN 4.5 V to 15 V, IOUT = 0 mA VO/ ILOAD VO eN eN VS = 5.0 V, 0 mA to 5 mA 1000 hrs @ +25C, VS = +15 V 0.1 Hz to 10 Hz at 1 kHz Electrical Specifications Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade (VS = 5 V, T A = 25 C TA 85 C unless otherwise noted) Min Typ 3 5 10 35 50 20 30 Max 8 15 25 125 150 125 150 Units ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA Symbol TCVO/C Conditions IOUT = 0 mA VO/VIN 4.5 V to 15 V, IOUT = 0 mA VO/ ILOAD VS = 5.0 V, 0 mA to 5 mA Electrical Specifications Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade SUPPLY CURRENT THERMAL HYSTERESIS NOTE Specifications subject to change without notice. (VS = 5 V, T A = 40 C TA 125 C unless otherwise noted) Min Typ 3 5 10 40 70 20 30 10 12 50 Max 10 20 30 200 250 200 300 15 18 Units ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA A A ppm Symbol TCVO/C Conditions IOUT = 0 mA VO/VIN 4.5 V to 15 V, IOUT = 0 mA VO/ ILOAD VS = 5.0 V, 0 mA to 5 mA @ +25C TO-92, SO-8, TSSOP-8 -4- REV. A ADR290/ADR291/ADR292 WAFER TEST LIMITS (@ I Parameter INITIAL ACCURACY ADR290 ADR291 ADR292 LINE REGULATION LOAD REGULATION SUPPLY CURRENT LOAD = 0 mA, TA = 25 C unless otherwise noted) Conditions Limits 2.042/2.054 2.494/2.506 4.090/4.102 VO + 1 V < VIN < 15 V, IOUT = 0 mA 0 to 5 mA, VIN = VO + 1 V ADR290, ADR291, No Load ADR292, No Load 125 125 12 15 Units V V V ppm/V ppm/mA A A Symbol VO VO VO VO/VIN VO/ILOAD NOTES Electrical tests are performed as wafer probe to the limits shown. Due to variations in assembly methods and normal yield loss, yield after packaging is not guaranteed for standard product dice. Consult factory to negotiate specifications based on dice lot qualification through sample lot assembly and testing. Specifications subject to change without notice. DICE CHARACTERISTICS Die Size 0.074 0.052 inch, 3848 sq. mils (1.88 1.32 mm, 2.48 sq. mm) Transistor Count: 52 1. V IN 2. GND 3. VOUT(FORCE) 4. VOUT(SENSE) For additional DICE ordering information, refer to databook. REV. A -5- ADR290/ADR291/ADR292 ABSOLUTE MAXIMUM RATINGS* *CAUTION Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 V Output Short-Circuit Duration . . . . . . . . . . . . . . . . . Indefinite Storage Temperature Range T9, R, RU Package . . . . . . . . . . . . . . . . . 65C to 150C Operating Temperature Range ADR290/ADR291/ADR292 . . . . . . . . . . . 40C to 125C Junction Temperature Range T9, R, RU Package . . . . . . . . . . . . . . . . . 65C to 125C Lead Temperature (Soldering, 60 sec) . . . . . . . . . . . . 300C Package Type 8-Lead SOIC (R) 8-Lead TO-92 (T9) 3-Pin TSSOP (RU) 1 JA 1. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation at or above this specification is not implied. Exposure to the above maximum rating conditions for extended periods may affect device reliability. 2. Remove power before inserting or removing units from their sockets. 3. Ratings apply to both DICE and packaged parts, unless otherwise noted JC Units C/W C/W C/W 158 162 240 43 120 43 NOTE 1 JA is specified for worst case conditions, i.e. JA is specified for device in socket for PDIP, and JA is specified for a device soldered in circuit board for SOIC packages. ORDERING GUIDE Model ADR290ER, ADR290FR, ADR290GR ADR290ER-REEL, ADR290FR-REEL, ADR290GR-REEL ADR290ER-REEL7, ADR290FR-REEL7, ADR290GR-REEL7 ADR290GT9 ADR290GT9-REEL ADR290GRU-REEL ADR290GRU-REEL7 ADR290GBC ADR291ER, ADR291FR, ADR291GR ADR291ER-REEL, ADR291FR-REEL, ADR291GR-REEL ADR291ER-REEL7, ADR291FR-REEL7, ADR291GR-REEL7 ADR291GT9 ADR291GT9-REEL ADR291GRU-REEL ADR291GRU-REEL7 ADR291GBC ADR292ER, ADR292FR, ADR292GR ADR292ER-REEL, ADR292FR-REEL, ADR292GR-REEL ADR292ER-REEL7, ADR292FR-REEL7, ADR292GR-REEL7 ADR292GT9 ADR292GT9-REEL ADR292GRU-REEL ADR292GRU-REEL7 ADR292GBC Temperature Range 40C to 40C to 40C to 40C to 40C to 40C to 40C to 25C 40C to 40C to 40C to 40C to 40C to 40C to 40C to 25C 40C to 40C to 40C to 40C to 40C to 40C to 40C to 25C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C 125C Package 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 3-Pin TO-92 3-Pin TO-92 8-Lead TSSOP 8-Lead TSSOP DICE 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 3-Pin TO-92 3-Pin TO-92 8-Lead TSSOP 8-Lead TSSOP DICE 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 3-Pin TO-92 3-Pin TO-92 8-Lead TSSOP 8-Lead TSSOP DICE 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 ADR290/ADR291/ADR292 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 -6- REV. A ADR290/ADR291/ADR292 2.054 VS = 5V 2.052 A OUTPUT VOLTAGE - V 3 TYPICAL PARTS 12 10 2.050 QUIESCENT CURRENT - TA = +125 C 14 8 6 4 TA = +25 C TA = -40 C 2.048 2.046 2.044 2 0 2.042 -50 -25 0 25 50 75 100 125 0 2 4 TEMPERATURE - C 6 8 10 INPUT VOLTAGE - V 12 14 16 Figure 1. ADR290 V OUT vs. Temperature Figure 4. ADR290 Quiescent Current vs. Input Voltage 2.506 VS = 5V 2.504 A OUTPUT VOLTAGE - V 3 TYPICAL PARTS 14 12 TA = +125 C 10 2.502 QUIESCENT CURRENT - 8 6 4 TA = +25 C TA = -40 C 2.500 2.498 2.496 2 0 2.494 -50 -25 0 25 50 75 100 125 0 2 4 TEMPERATURE - C 6 8 10 INPUT VOLTAGE - V 12 14 16 Figure 2. ADR291 V OUT vs. Temperature Figure 5. ADR291 Quiescent Current vs. Input Voltage 4.102 VS = 5V 4.100 3 TYPICAL PARTS 16 14 12 10 8 6 4 2 0 A TA = +125 C TA = +25 C TA = -40 C OUTPUT VOLTAGE - V 4.098 4.096 4.094 4.092 4.090 -50 -25 0 25 50 75 100 125 QUIESCENT CURRENT - 0 2 4 TEMPERATURE - C 6 8 10 INPUT VOLTAGE - V 12 14 16 Figure 3. ADR292 V OUT vs. Temperature Figure 6. ADR292 Quiescent Current vs. Input Voltage REV. A -7- ADR290/ADR291/ADR292 14 VS = 5V DIFFERENTIAL VOLTAGE - V 12 A ADR292 ADR291 0.7 0.6 0.5 TA = +125 C 0.4 0.3 0.2 TA = +25 C TA = -40 C SUPPLY CURRENT - 10 8 ADR290 6 0.1 4 -50 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 LOAD CURRENT - mA 4.0 4.5 5.0 -25 0 25 50 75 100 125 TEMPERATURE - C Figure 7. ADR290/ADR291/ADR292 Supply Current vs. Temperature Figure 10. ADR290 Minimum Input-Output Voltage Differential vs. Load Current 100 ADR290: VS = 2.7V TO 15V ADR291: VS = 3.0V TO 15V ADR292: VS = 4.5V TO 15V LINE REGULATION - ppm/V 0.7 IOUT = 0mA 0.6 DIFFERENTIAL VOLTAGE - V TA = +125 C 0.5 TA = +25 C 0.4 0.3 TA = -40 C 0.2 80 60 ADR292 40 20 ADR290 ADR291 0 -50 -25 0 25 50 75 100 125 0.1 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 LOAD CURRENT - mA 4.0 4.5 5.0 TEMPERATURE - C Figure 8. ADR290/ADR291/ADR292 Line Regulation vs. Temperature Figure 11. ADR291 Minimum Input-Output Voltage Differential vs. Load Current 100 ADR290: VS = 2.7V TO 7.0V ADR291: VS = 3.0V TO 7.0V ADR292: VS = 4.5V TO 9.0V LINE REGULATION - ppm/V 80 IOUT = 0mA 0.7 0.6 DIFFERENTIAL VOLTAGE - V TA = +125 C 0.5 TA = +25 C 0.4 0.3 0.2 60 ADR291 40 ADR290 TA = -40 C 20 ADR292 0.1 0 -50 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 LOAD CURRENT - mA 4.0 4.5 5.0 -25 0 25 50 75 100 125 TEMPERATURE - C Figure 9. ADR290/ADR291/ADR292 Line Regulation vs. Temperature Figure 12. ADR292 Minimum Input-Output Voltage Differential vs. Load Current -8- REV. A ADR290/ADR291/ADR292 200 VS = 5V LINE REGULATION - ppm/mA V VOUT FROM NOMINAL - 0 160 250 500 120 IOUT = 1mA TA = +25 C -250 TA = +125 C -500 TA = -40 C 80 40 IOUT = 5mA 0 -50 -750 -25 0 25 50 75 100 125 -1000 0.1 TEMPERATURE - C 1 SOURCING LOAD CURRENT - mA 10 Figure 13. ADR290 Line Regulation vs. Temperature Figure 16. ADR290 VOUT from Nominal vs. Load Current 200 VS = 5V LOAD REGULATION - ppm/mA 160 V 0 -250 TA = +25 C -500 -750 TA = -40 C -1000 -1250 -1500 -1750 TA = +125 C IOUT = 1mA 120 IOUT = 5mA 80 40 0 -50 VOUT FROM NOMINAL - 125 -25 0 25 50 75 100 -2000 0.1 TEMPERATURE - C 1 SOURCING LOAD CURRENT - mA 10 Figure 14. ADR291 Load Regulation vs. Temperature Figure 17. ADR291 VOUT from Nominal vs. Load Current 200 VS = 5V LOAD REGULATION - ppm/mA V 160 0 -500 -1000 VOUT FROM NOMINAL - -1500 -2000 -2500 -3000 -3500 TA = -40 C TA = +25 C TA = +125 C 120 IOUT = 1mA IOUT = 5mA 80 40 0 -50 -25 0 25 50 75 100 125 -4000 0.1 TEMPERATURE - C 1 SOURCING LOAD CURRENT - mA 10 Figure 15. ADR292 Load Regulation vs. Temperature Figure 18. ADR292 VOUT from Nominal vs. Load Current REV. A -9- ADR290/ADR291/ADR292 1000 900 VOLTAGE NOISE DENSITY - nV/ Hz 800 OUTPUT IMPEDANCE - 700 ADR291 600 500 400 300 200 100 0 10 100 FREQUENCY - Hz 1000 0 0 10 100 FREQUENCY - Hz 1k 10k ADR290 ADR292 VIN = 15V TA = 25 C 40 50 VS = 5V IL = 0 mA 30 20 10 Figure 19. Voltage Noise Density vs. Frequency Figure 22. ADR290 Output Impedance vs. Frequency 120 VS = 5V 100 50 VS = 5V IL = 0 mA 40 RIPPLE REJECTION - dB 80 OUTPUT IMPEDANCE - 100 FREQUENCY - Hz 1000 30 60 20 40 20 10 0 10 0 0 10 100 FREQUENCY - Hz 1k 10k Figure 20. ADR290/ADR291/ADR292 Ripple Rejection vs. Frequency Figure 23. ADR291 Output Impedance vs. Frequency 50 1s 40 100 90 VS = 5V IL = 0 mA OUTPUT IMPEDANCE - TIME - sec 30 2 VP-P 20 10 0% 10 0 0 10 100 FREQUENCY - Hz 1k 10k Figure 21. ADR290 0.1 Hz to 10 Hz Noise Figure 24. ADR292 Output Impedance vs. Frequency -10- REV. A ADR290/ADR291/ADR292 IL = 5mA OFF ON 100 90 100 90 1ms IL = 5mA 500 s 10 0% 10 0% 1V 1V Figure 25. ADR291 Load Transient Figure 28. ADR291 Turn-On Time IL = 5mA CL = 1nF OFF ON 100 90 1ms 100 90 IL = 0mA 10ms 10 0% 10 0% 1V 1V Figure 26. ADR291 Load Transient Figure 29. ADR291 Turn-Off Time IL = 5mA CL = 100nF OFF ON 100 90 5ms 10 0% 1V Figure 27. ADR291 Load Transient REV. A -11- ADR290/ADR291/ADR292 THEORY OF OPERATION Device Power Dissipation Considerations The ADR29x series of references uses a new reference generation technique known as XFET (eXtra implanted junction FET). This technique yields a reference with low noise, low supply current and very low thermal hysteresis. The core of the XFET reference consists of two junction fieldeffect transistors, one of which has an extra channel implant to raise its pinch-off voltage. By running the two JFETS at the same drain current, the difference in pinch-off voltage can be amplified and used to form a highly stable voltage reference. The intrinsic reference voltage is around 0.5 V with a negative temperature coefficient of about -120 ppm/K. This slope is essentially locked to the dielectric constant of silicon and can be closely compensated by adding a correction term generated in the same fashion as the proportional-to-temperature (PTAT) term used to compensate bandgap references. The big advantage over a bandgap reference is that the intrinsic temperature coefficient is some thirty times lower (therefore less correction is needed) and this results in much lower noise since most of the noise of a bandgap reference comes from the temperature compensation circuitry. The simplified schematic below shows the basic topology of the ADR29x series. The temperature correction term is provided by a current source with value designed to be proportional to absolute temperature. The general equation is: R1 + R2 + R3 VOUT = VP + I PTAT R3 R1 The ADR29x family of references is guaranteed to deliver load currents to 5 mA with an input voltage that ranges from 2.7 V to 15 V (minimum supply voltage depends on output voltage option). When these devices are used in applications with large input voltages, care should be exercised to avoid exceeding the published specifications for maximum power dissipation or junction temperature that could result in premature device failure. The following formula should be used to calculate a device's maximum junction temperature or dissipation: PD = TJ - TA JA In this equation, TJ and TA are the junction and ambient temperatures, respectively, PD is the device power dissipation, and JA is the device package thermal resistance. Basic Voltage Reference Connections References, in general, require a bypass capacitor connected from the VOUT pin to the GND pin. The circuit in Figure 31 illustrates the basic configuration for the ADR29x family of references. Note that the decoupling capacitors are not required for circuit stability. NC 1 2 8 7 NC NC OUTPUT + 10 F NC 0.1 F 4 5 NC 3 6 0.1 F ( )( ) ADR29x where VP is the difference in pinch-off voltage between the two FETs, and IPTAT is the positive temperature coefficient correction current. The various versions of the ADR29x family are created by on-chip adjustment of R1 and R3 to achieve 2.048 V, 2.500 V or 4.096 V at the reference output. The process used for the XFET reference also features vertical NPN and PNP transistors, the latter of which are used as output devices to provide a very low drop-out voltage. VIN I1 I1 Figure 31. Basic Voltage Reference Configuration Noise Performance The noise generated by the ADR29x family of references is typically less than 12 V p-p over the 0.1 Hz to 10 Hz band. Figure 21 shows the 0.1 Hz to 10 Hz noise of the ADR290 which is only 6 V p-p. The noise measurement is made with a bandpass filter made of a 2-pole high-pass filter with a corner frequency at 0.1 Hz and a 2-pole low-pass filter with a corner frequency at 10 Hz. Turn-On Time * VP R1 VOUT IPTAT R2 Upon application of power (cold start), the time required for the output voltage to reach its final value within a specified error band is defined as the turn-on settling time. Two components normally associated with this are the time for the active circuits to settle, and the time for the thermal gradients on the chip to stabilize. Figure 28 shows the turn-on settling time for the ADR291. APPLICATIONS SECTION A Negative Precision Reference without Precision Resistors R3 GND *EXTRA CHANNEL IMPLANT VOUT R1 R2 R3 R1 VP I PTAT R3 Figure 30. ADR290/ADR291/ADR292 Simplified Schematic In many current-output CMOS DAC applications, where the output signal voltage must be of the same polarity as the reference voltage, it is often required to reconfigure a current-switching DAC into a voltage-switching DAC through the use of a 1.25 V reference, an op amp and a pair of resistors. Using a current-switching DAC directly requires the need for an additional operational amplifier at the output to reinvert the signal. A negative voltage reference is then desirable from the point that -12- REV. A ADR290/ADR291/ADR292 an additional operational amplifier is not required for either reinversion (current-switching mode) or amplification (voltageswitching mode) of the DAC output voltage. In general, any positive voltage reference can be converted into a negative voltage reference through the use of an operational amplifier and a pair of matched resistors in an inverting configuration. The disadvantage to that approach is that the largest single source of error in the circuit is the relative matching of the resistors used. The circuit illustrated in Figure 32 avoids the need for tightly matched resistors with the use of an active integrator circuit. In this circuit, the output of the voltage reference provides the input drive for the integrator. The integrator, to maintain circuit equilibrium adjusts its output to establish the proper relationship between the reference's VOUT and GND. Thus, any negative output voltage desired can be chosen by simply substituting for the appropriate reference IC. One caveat with this approach should be mentioned: although rail-to-rail output amplifiers work best in the application, these operational amplifiers require a finite amount (mV) of headroom when required to provide any load current. The choice for the circuit's negative supply should take this issue into account. VIN VIN 2 ADR29x 6 VOUT R1 GND 4 1F ISY ADJUST P1 IOUT RL RSET Figure 33. A Precision Current Source High Voltage Floating Current Source The circuit of Figure 34 can be used to generate a floating current source with minimal self heating. This particular configuration can operate on high supply voltages determined by the breakdown voltage of the N-channel JFET. +VS E231 SILICONIX 2 ADR29x 1k 6 1F +5V 100 VOUT GND 4 100k 1F A1 -VREF -5V VIN ADR290 A1 = 1/2 OP291, 1/2 OP295 2N3904 Figure 32. A Negative Precision Voltage Reference Uses No Precision Resistors A Precision Current Source OP90 GND 2.10k Many times in low power applications, the need arises for a precision current source that can operate on low supply voltages. As shown in Figure 33, any one of the devices in the ADR29x family of references can be configured as a precision current source. The circuit configuration illustrated is a floating current source with a grounded load. The reference's output voltage is bootstrapped across RSET, which sets the output current into the load. With this configuration, circuit precision is maintained for load currents in the range from the reference's supply current, typically 12 A to approximately 5 mA. -VS Figure 34. High Voltage Floating Current Source Kelvin Connections In many portable instrumentation applications, where PC board cost and area go hand-in-hand, circuit interconnects are very often of dimensionally minimum width. These narrow lines can cause large voltage drops if the voltage reference is required to provide load currents to various functions. In fact, a circuit's interconnects can exhibit a typical line resistance of 0.45 mW/square (1 oz. Cu, for example). Force and sense connections also referred to as Kelvin connections, offer a convenient method of eliminating the effects of voltage drops in circuit wires. Load currents flowing through wiring resistance produce an error (VERROR = R IL ) at the load. However, the Kelvin connection of Figure 35, overcomes the problem by including the wiring resistance within the forcing loop of the op amp. Since the op amp senses the load voltage, op amp loop control forces the output to compensate for the wiring error and to produce the correct voltage at the load. REV. A -13- ADR290/ADR291/ADR292 VIN RLW 2 VIN RLW +VOUT FORCE RL 1F 100k +VOUT SENSE Voltage Regulator For Portable Equipment ADR29x A1 6 VOUT GND 4 A1 = 1/2 OP295 Figure 35. Advantage of Kelvin Connection Low Power, Low Voltage Reference For Data Converters The ADR29x family of references is ideal for providing a stable, low cost and low power reference voltage in portable equipment power supplies. Figure 37 shows how the ADR290/ADR291/ ADR292 can be used in a voltage regulator that not only has low output noise (as compared to switch mode design) and low power, but also a very fast recovery after current surges. Some precautions should be taken in the selection of the output capacitors. Too high an ESR (Effective Series Resistance) could endanger the stability of the circuit. A solid tantalum capacitor, 16 V or higher, and an aluminum electrolytic capacitor, 10 V or higher, are recommended for C1 and C2, respectively. Also, the path from the ground side of C1 and C2 to the ground side of R1 should be kept as short as possible. CHARGER INPUT The ADR29x family has a number of features that makes it ideally suited for use with A/D and D/A converters. The low supply voltage required makes it possible to use the ADR29x with today's converters that run on 3 V supplies without having to add a higher supply voltage for the reference. The low quiescent current (12 A max) and low noise, tight temperature coefficient, combined with the high accuracy of the ADR29x makes it ideal for low power applications such as hand-held, battery operated equipment. One such ADC for which the ADR291 is well suited is the AD7701. Figure 36 shows the ADR291 used as the reference for this converter. The AD7701 is a 16-bit A/D converter with on-chip digital filtering intended for the measurement of wide dynamic range, low frequency signals such as those representing chemical, physical or biological processes. It contains a charge balancing (sigma-delta) ADC, calibration microcontroller with on-chip static RAM, a clock oscillator and a serial communications port. This entire circuit runs on 5 V supplies. The power dissipation of the AD7701 is typically 25 mW and, when combined with the power dissipation of the ADR291 (60 W), the entire circuit still consumes about 25 mW. +5V ANALOG SUPPLY 0.1 F 2 VIN 6V V OUT 6 + ADR29x TEMP 3 GND 4 R1 402k 1% R2 402k 1% C1 68 F TANT + 3 4 2 7 6 OP20 +5V, 100mA + C2 1000 F ELECT IRF9530 R3 510k LEAD-ACID BATTERY Figure 37. Voltage Regulator for Portable Equipment 0.1 F 10 F AVDD VIN VOUT DVDD VREF SLEEP MODE 0.1 F 0.1 F ADR291 GND AD7701 RANGES SELECT CALIBRATE ANALOG INPUT ANALOG GROUND 0.1 F AVSS -5V ANALOG SUPPLY BP/UP CAL DRDY CS SCLK SDATA DATA READY READ (TRANSMIT) SERIAL CLOCK SERIAL CLOCK CLKIN AIN AGND CLKOUT SC1 SC2 DGND 0.1 F DVSS 0.1 F 10 F Figure 36. Low Power, Low Voltage Supply Reference for the AD7701 -14- REV. A ADR290/ADR291/ADR292 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 8-Lead Narrow Body SO (R Suffix) 0.1968 (5.00) 0.1890 (4.80) 8 5 0.2440 (6.20) 0.2284 (5.80) 1 4 0.1574 (4.00) 0.1497 (3.80) PIN 1 0.102 (2.59) 0.094 (2.39) 0.0196 (0.50) x 45 0.0099 (0.25) 0.0098 (0.25) 0.0040 (0.10) 0.0500 0.0192 (0.49) SEATING (1.27) 0.0138 (0.35) 0.0098 (0.25) PLANE BSC 0.0075 (0.19) 8 0 0.0500 (1.27) 0.0160 (0.41) 8-Lead TSSOP (RU Suffix) 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) 3-Pin TO-92 (T9 Suffix) 0.135 (3.43) MIN 0.205 (5.20) 0.175 (4.96) 0.210 (5.33) 0.170 (4.38) SEATING PLANE 0.050 (1.27) MAX 0.500 (12.70) MIN 0.019 (0.482) 0.016 (0.407) SQUARE 0.105 (2.66) 0.095 (2.42) 0.105 (2.66) 0.080 (2.42) 0.055 (1.39) 0.045 (1.15) 0.105 (2.66) 0.080 (2.42) 1 2 3 0.165 (4.19) 0.125 (3.94) BOTTOM VIEW REV. A -15- PRINTED IN U.S.A. C3151-0-2/00 (rev. A) |
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