ADR423AR

a Ultraprecision Low Noise, 2.048 V/2.500 V/ 3.00 V/5.00 V XFET® Voltage References ADR420/ADR421/ADR423/ADR425 PIN CONFIGURATION Surface-Mount Packages 8-Lead SOIC 8-Lead Mini_SOIC TP 1 VIN 2 NIC 3 8 TP FEATURES Low Noise (0.1 Hz to 10 Hz) ADR420: 1.75 V p-p ADR421: 1.75 V p-p ADR423: 2.0 V p-p ADR425: 3.4 V p-p Low Temperature Coefficient: 3 ppm/ C Long-Term Stability: 50 ppm/1000 Hours Load Regulation: 70 ppm/mA Line Regulation: 35 ppm/V Low Hysteresis: 40 ppm Typical Wide Operating Range ADR420: 4 V to 18 V ADR421: 4.5 V to 18 V ADR423: 5 V to 18 V ADR425: 7 V to 18 V Quiescent Current: 0.5 mA Maximum High Output Current: 10 mA Wide Temperature Range: –40 C to +125 C APPLICATIONS Precision Data Acquisition Systems High-Resolution Converters Battery-Powered Instrumentation Portable Medical Instruments Industrial Process Control Systems Precision Instruments Optical Network Control Circuits GENERAL DESCRIPTION ADR42x 7 NIC 6V OUT TOP VIEW GND 4 (Not to Scale) 5 TRIM NIC = NO INTERNAL CONNECTION TP = TEST PIN (DO NOT CONNECT) Table I. ADR42x Products The ADR42x series are ultraprecision second-generation XFET voltage references featuring low noise, high accuracy, and excellent long-term stability in a SOIC and Mini_SOIC footprints. Patented temperature drift curvature correction technique and XFET (eXtra implanted junction FET) technology minimize nonlinearity of the voltage change with temperature. The XFET architecture offers superior accuracy and thermal hysteresis to the bandgap references. It also operates at lower power and lower supply headroom than the Buried Zener references. The superb noise, stable, and accurate characteristics of ADR42x make them ideal for precision conversion applications such as optical network and medical equipment. The ADR42x trim terminal can also be used to adjust the output voltage over a ± 0.5% range without compromising any other performance. The ADR42x series voltage references offer two electrical grades and are specified over the extended industrial temperature range of –40°C to +125°C. Devices are available in 8-lead SOIC-8 or 30% smaller 8-lead Mini_SOIC-8 packages. XFET is a registered trademark of Analog Devices, Inc. ADR420 Products ADR420 ADR421 ADR423 ADR425 Output Voltage VO 2.048 2.50 3.00 5.00 Initial Accuracy mV % 1, 3 1, 3 1.5, 4 2, 6 0.05, 0.15 0.04, 0.12 0.04, 0.12 0.04, 0.12 Tempco ppm/°C 3, 10 3, 10 3, 10 3, 10 R EV. B 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. 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 www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 2002 ADR42x–SPECIFICATIONS ADR420 ELECTRICAL SPECIFICATIONS Parameter Output Voltage Initial Accuracy Output Voltage Initial Accuracy A Grade Symbol VO VOERR VO VOERR TCVO VIN – VO ∆VO/∆VIN ∆VO/∆ILOAD IIN eN p-p eN tR ∆VO VO_HYS RRR ISC –40°C < TA < +125°C 2 VIN = 5 V to 18 V –40°C < TA < +125°C ILOAD = 0 mA to 10 mA –40°C < TA < +125°C No Load –40°C < TA < +125°C 0.1 Hz to 10 Hz 1 kHz 1,000 Hours fIN = 10 kHz 10 35 70 390 1.75 60 10 50 40 75 27 500 600 (@ VIN = 5.0 V to 15.0 V, TA = 25 C, unless otherwise noted.) Conditions Min 2.045 –3 –0.15 2.047 –1 –0.05 Typ 2.048 Max 2.051 +3 +0.15 2.049 +1 +0.05 10 3 Unit V mV % V mV % ppm/°C ppm/°C V ppm/V ppm/mA µA µA µV p-p nV/√Hz µs ppm ppm dB mA B Grade 2.048 Temperature Coefficient A Grade B Grade Supply Voltage Headroom Line Regulation Load Regulation Quiescent Current Voltage Noise Voltage Noise Density Turn-On Settling Time Long-Term Stability Output Voltage Hysteresis Ripple Rejection Ratio Short Circuit to GND Specifications subject to change without notice. 2 1 ADR421 ELECTRICAL SPECIFICATIONS Parameter Output Voltage Initial Accuracy Output Voltage Initial Accuracy A Grade Symbol VO VOERR VO VOERR TCVO VIN – VO ∆VO/∆VIN ∆VO/∆ILOAD IIN eN p-p eN tR ∆VO VO_HYS RRR ISC (@ VIN = 5.0 V to 15.0 V, TA = 25 C, unless otherwise noted.) Conditions Min 2.497 –3 –0.12 2.499 –1 –0.04 –40°C < TA < +125°C 2 VIN = 5 V to 18 V –40°C < TA < +125°C ILOAD = 0 mA to 10 mA –40°C < TA < +125°C No Load –40°C < TA < +125°C 0.1 Hz to 10 Hz 1 kHz 1,000 Hours fIN = 10 kHz 10 35 70 390 1.75 80 10 50 40 75 27 500 600 Typ 2.500 Max 2.503 +3 +0.12 2.501 +1 +0.04 10 3 Unit V mV % V mV % ppm/°C ppm/°C V ppm/V ppm/mA µA µA µV p-p nV/√Hz µs ppm ppm dB mA B Grade 2.500 Temperature Coefficient A Grade B Grade Supply Voltage Headroom Line Regulation Load Regulation Quiescent Current Voltage Noise Voltage Noise Density Turn-On Settling Time Long-Term Stability Output Voltage Hysteresis Ripple Rejection Ratio Short Circuit to GND Specifications subject to change without notice. 2 1 –2– REV. B ADR420/ADR421/ADR423/ADR425 ADR423 ELECTRICAL SPECIFICATIONS Parameter Output Voltage Initial Accuracy Output Voltage Initial Accuracy A Grade Symbol VO VOERR VO VOERR TCVO VIN − VO ∆VO/∆VIN ∆VO/∆ILOAD IIN eN p-p eN tR ∆VO VO_HYS RRR ISC –40°C < TA < +125°C 2 VIN = 5 V to 18 V –40°C < TA < +125°C ILOAD = 0 mA to 10 mA –40°C < TA < +125°C No Load –40°C < TA < +125°C 0.1 Hz to 10 Hz 1 kHz 1,000 Hours fIN = 10 kHz 10 35 70 390 2 90 10 50 40 75 27 500 600 (@ VIN = 5.0 V to 15.0 V, TA = 25 C, unless otherwise noted.) Conditions Min 2.996 –4 –0.13 2.9985 –1.5 –0.04 Typ 3.000 Max 3.004 +4 +0.13 3.0015 +1.5 +0.04 10 3 Unit V mV % V mV % ppm/°C ppm/°C V ppm/V ppm/mA µA µA µV p-p nV/√Hz µs ppm ppm dB mA B Grade 3.000 Temperature Coefficient A Grade B Grade Supply Voltage Headroom Line Regulation Load Regulation Quiescent Current Voltage Noise Voltage Noise Density Turn-On Settling Time Long-Term Stability Output Voltage Hysteresis Ripple Rejection Ratio Short Circuit to GND Specifications subject to change without notice. 2 1 ADR425 ELECTRICAL SPECIFICATIONS (@ V Parameter Output Voltage Initial Accuracy Output Voltage Initial Accuracy A Grade Symbol VO VOERR VO VOERR TCVO VIN – VO ∆VO/∆VIN ∆VO/∆ILOAD IIN eN p-p eN tR ∆VO VO_HYS RRR ISC IN = 7.0 V to 15.0 V, TA = 25 C, unless otherwise noted.) Min 4.994 –6 –0.12 4.998 –2 –0.04 Typ 5.000 Max 5.006 +6 +0.12 5.002 +2 +0.04 10 3 35 70 390 3.4 110 10 50 40 75 27 500 600 Unit V mV % V mV % ppm/°C ppm/°C V ppm/V ppm/mA µA µA µV p-p nV/√Hz µs ppm ppm dB mA Conditions B Grade 5.000 Temperature Coefficient A Grade B Grade Supply Voltage Headroom Line Regulation Load Regulation Quiescent Current Voltage Noise Voltage Noise Density Turn-On Settling Time Long-Term Stability Output Voltage Hysteresis Ripple Rejection Ratio Short Circuit to GND Specifications subject to change without notice. –40°C < TA < +125°C 2 VIN = 7 V to 18 V –40°C < TA < +125°C ILOAD = 0 mA to 10 mA –40°C < TA < +125°C No Load –40°C < TA < +125°C 0.1 Hz to 10 Hz 1 kHz 1,000 Hours fIN = 10 kHz 2 1 10 REV. B –3– ADR420/ADR421/ADR423/ADR425 ABSOLUTE MAXIMUM RATINGS * PIN FUNCTION DESCRIPTIONS Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 V Output Short-Circuit Duration to GND . . . . . . . . . Indefinite Storage Temperature Range R, RM Packages . . . . . . . . . . . . . . . . . . . . –65°C to +150°C Operating Temperature Range ADR42x . . . . . . . . . . . . . . . . . . . . . . . . . . –40°C to +125°C Junction Temperature Range R, RM Packages . . . . . . . . . . . . . . . . . . . . –65°C to +150°C Lead Temperature Range (Soldering, 60 sec) . . . . . . . 300°C *Absolute maximum ratings apply at 25 °C, unless otherwise noted. Pin 1, 8 Mnemonic Description TP Test Pin. There are actual connections in TP pins but they are reserved for factory testing purposes. Users should not connect anything to TP pins, otherwise the device may not function properly. Input Voltage No Internal Connect. NICs have no internal connections. Ground Pin = 0 V Trim Terminal. It can be used to adjust the output voltage over a ± 0.5% range without affecting the temperature coefficient. Output Voltage θJA* 190 130 Unit °C/W °C/W 2 3, 7 4 5 VIN NIC GND TRIM PIN CONFIGURATIONS SOIC-8 TP 1 VIN 2 NIC 3 GND 4 8 TP Mini_SOIC-8 TP 1 VIN 2 NIC 3 GND 4 8 TP 6 VOUT ADR42x 7 NIC 6 ADR42x 7 NIC 6 VOUT VOUT Package Type 8-Lead Mini_SOIC (RM) 8-Lead SOIC (R) 5 TRIM 5 TRIM NIC = NO INTERNAL CONNECTION TP = TEST PIN (DO NOT CONNECT) NIC = NO INTERNAL CONNECTION TP = TEST PIN (DO NOT CONNECT) *θJA is specified for the worst-case conditions, i.e., θJA is specified for device soldered in circuit board for surface-mount packages. ORDERING GUIDE Model ADR420AR ADR420AR-Reel7 ADR420BR ADR420BR-Reel7 ADR420ARM-Reel7 ADR421AR ADR421AR-Reel7 ADR421BR ADR421BR-Reel7 ADR421ARM-Reel7 ADR423AR ADR423AR-Reel7 ADR423BR ADR423BR-Reel7 ADR423ARM-Reel7 ADR425AR ADR425AR-Reel7 ADR425BR ADR425BR-Reel7 ADR425ARM-Reel7 Output Voltage VO 2.048 2.048 2.048 2.048 2.048 2.50 2.50 2.50 2.50 2.50 3.00 3.00 3.00 3.00 3.00 5.00 5.00 5.00 5.00 5.00 Initial Accuracy mV % 3 3 1 1 3 3 3 1 1 3 4 4 1.5 1.5 4 6 6 2 2 6 0.15 0.15 0.05 0.05 0.15 0.12 0.12 0.04 0.04 0.12 0.13 0.13 0.04 0.04 0.13 0.12 0.12 0.04 0.04 0.12 Temperature Coefficient Package ppm/°C Description 10 10 3 3 10 10 10 3 3 10 10 10 3 3 10 10 10 3 3 10 SOIC SOIC SOIC SOIC Mini_SOIC SOIC SOIC SOIC SOIC Mini_SOIC SOIC SOIC SOIC SOIC Mini_SOIC SOIC SOIC SOIC SOIC Mini_SOIC Package Top Option Mark SO-8 SO-8 SO-8 SO-8 RM-8 SO-8 SO-8 SO-8 SO-8 RM-8 SO-8 SO-8 SO-8 SO-8 RM-8 SO-8 SO-8 SO-8 SO-8 RM-8 ADR420 ADR420 ADR420 ADR420 R4A ADR421 ADR421 ADR421 ADR421 R5A ADR423 ADR423 ADR423 ADR423 Number of Parts per Reel 98 3,000 98 3,000 1,000 98 3,000 98 3,000 1,000 98 3,000 98 3,000 1,000 98 3,000 98 3,000 1,000 Temperature Range °C –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 –40 to +125 ADR425 ADR425 ADR425 ADR425 R7A 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 AD42x 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 –4– REV. B ADR420/ADR421/ADR423/ADR425 PARAMETER DEFINITIONS Temperature Coefficient Thermal Hysteresis The change of output voltage over the operating temperature range and normalized by the output voltage at 25°C, expressed in ppm/°C. The equation follows: Thermal hysteresis is defined as the change of output voltage after the device is cycled through temperature from +25°C to –40°C to +125°C and back to +25 ° C. This is a typical value from a sample of parts put through such a cycle. VO _ HYS = VO (25°C ) – VO _ TC VO _ HYS ( ppm ) = VO (25°C ) – VO _ TC VO (25°C ) × 106 TCVO ( ppm / °C ) = where VO (25°C) = VO at 25°C VO (T2 ) – VO (T1 ) × 106 VO (25°C ) × (T2 – T1 ) where VO (25°C) = VO at 25°C VO_TC = VO at 25°C after temperature cycle at +25°C to –40°C to +125°C and back to +25°C. Input Capacitor VO (T1) = VO at Temperature 1 VO (T2) = VO at Temperature 2. Line Regulation The change in output voltage due to a specified change in input voltage. It includes the effects of self-heating. Line regulation is expressed in either percent per volt, parts-per-million per volt, or microvolts per volt change in input voltage Load Regulation The change in output voltage due to a specified change in load current. It includes the effects of self-heating. Load regulation is expressed in either microvolts per milliampere, parts-per-million per milliampere, or ohms of dc output resistance. Long-Term Stability Input capacitors are not required on the ADR42x. There is no limit for the value of the capacitor used on the input, but a 1 µF to 10 µF capacitor on the input will improve transient response in applications where the supply suddenly changes. An additional 0.1 µF in parallel will also help to reduce noise from the supply. Output Capacitor Typical shift of output voltage at 25°C on a sample of parts subjected to operation life test of 1000 hours at 125°C: ∆VO = VO (t0 ) – VO (t1 ) ∆VO ( ppm) = where VO (t0) = VO at 25°C at Time 0 VO (t1) = VO at 25°C after 1,000 hours operation at 125°C. VO (t0 ) – VO (t1 ) × 10 6 VO (t0 ) The ADR42x does not need output capacitors for stability under any load condition. An output capacitor, typically 0.1 µF, will filter out any low-level noise voltage and will not affect the operation of the part. On the other hand, the load transient response can be improved with an additional 1 µF to 10 µF output capacitor in parallel. A capacitor here will act as a source of stored energy for sudden increase in load current. The only parameter that will degrade, by adding an output capacitor, is turn-on time and it depends on the size of the capacitor chosen. REV. B –5– ADR420/ADR421/ADR423/ADR425 Characteristics DR42x Series–Typical Performance 2.0495 2.0493 2.0491 2.0489 VOUT – V VOUT – V 5.0025 5.0023 5.0021 5.0019 5.0017 5.0015 5.0013 5.0011 5.0009 5.0007 5.0005 –40 –10 20 40 TEMPERATURE – C 80 110 125 2.0487 2.0485 2.0483 2.0481 2.0479 2.0477 2.0475 –40 –10 20 50 80 110 125 TEMPERATURE – C TPC 1. ADR420 Typical Output Voltage vs. Temperature TPC 4. ADR425 Typical Output Voltage vs. Temperature 2.5015 2.5013 2.5011 2.5009 VOUT – V SUPPLY CURRENT – mA 0.55 0.50 +125 C 0.45 +25 C 0.40 –40 C 2.5007 2.5005 2.5003 2.5001 2.4999 2.4997 2.4995 –40 0.35 0.30 0.25 –10 20 50 TEMPERATURE – C 80 110 125 4 6 8 10 INPUT VOLTAGE – V 12 14 15 TPC 2. ADR421 Typical Output Voltage vs. Temperature TPC 5. ADR420 Supply Current vs. Input Voltage 3.0010 3.0008 3.0006 3.0004 0.55 0.50 SUPPLY CURRENT – mA 0.45 +125 C 0.40 +25 C 0.35 –40 C 0.30 VOUT – V 3.0002 3.0000 2.9998 2.9996 2.9994 2.9992 2.9990 –40 –10 20 40 TEMPERATURE – C 80 110 125 0.25 4 6 8 10 INPUT VOLTAGE – V 12 14 15 TPC 3. ADR423 Typical Output Voltage vs. Temperature TPC 6. ADR421 Supply Current vs. Input Voltage –6– REV. B ADR420/ADR421/ADR423/ADR425 0.55 70 IL = 0mA TO 5mA LOAD REGULATION – ppm/mA 0.50 SUPPLY CURRENT – mA 60 50 VIN = 5V 40 0.45 +125 C 0.40 +25 C 0.35 –40 C 0.30 30 VIN = 6.5V 20 10 0.25 4 6 8 10 INPUT VOLTAGE – V 12 14 15 0 –40 –10 20 50 TEMPERATURE – C 80 110 125 TPC 7. ADR423 Supply Current vs. Input Voltage TPC 10. ADR421 Load Regulation vs. Temperature 0.55 70 IL = 0mA TO 10mA 60 LOAD REGULATION – ppm/mA 0.50 SUPPLY CURRENT – mA +125 C 0.45 50 VIN = 7V 40 VIN = 15V 30 0.40 +25 C 0.35 –40 C 0.30 20 10 0.25 6 8 10 12 INPUT VOLTAGE – V 14 15 0 –40 –10 20 40 TEMPERATURE – C 80 110 125 TPC 8. ADR425 Supply Current vs. Input Voltage TPC 11. ADR423 Load Regulation vs. Temperature 70 IL = 0mA TO 5mA 60 LOAD REGULATION – ppm/mA 35 30 VIN = 15V IL = 0mA TO 10mA 50 40 VIN = 4.5V LOAD REGULATION – ppm/mA 25 20 15 30 20 10 VIN = 6V 10 5 0 –40 –10 20 50 TEMPERATURE – C 80 110 125 0 –40 –10 20 40 TEMPERATURE – C 80 110 125 TPC 9. ADR420 Load Regulation vs. Temperature TPC 12. ADR425 Load Regulation vs. Temperature REV. B –7– ADR420/ADR421/ADR423/ADR425 6 VIN = 4.5V TO 15V 5 LINE REGULATION – ppm/V LINE REGULATION – ppm/V 14 VIN = 7.5V TO 15V 12 10 8 6 4 2 0 –40 4 3 2 1 0 –40 –10 20 50 80 110 125 –10 TEMPERATURE – C 20 50 TEMPERATURE – C 80 110 125 TPC 13. ADR420 Line Regulation vs. Temperature TPC 16. ADR425 Line Regulation vs. Temperature 6 VIN = 5V TO 15V 5 2.5 LINE REGULATION – ppm/V DIFFERENTIAL VOLTAGE – V 2.0 –40 C +25 C 1.5 +85 C 1.0 4 3 2 0.5 1 0 –40 0 –10 20 50 TEMPERATURE – C 80 110 125 0 1 2 3 LOAD CURRENT – mA 4 5 TPC 14. ADR421 Line Regulation vs. Temperature TPC 17. ADR420 Minimum Input-Output Voltage Differential vs. Load Current 9 VIN = 5V TO 15V 8 DIFFERENTIAL VOLTAGE – V LINE REGULATION – ppm/V 2.5 7 6 5 4 3 2 1 0 –40 2.0 –40 C +25 C 1.5 +125 C 1.0 0.5 –10 20 50 TEMPERATURE – C 80 110 0 0 1 2 3 LOAD CURRENT – mA 4 5 TPC 15. ADR423 Line Regulation vs. Temperature TPC 18. ADR421 Minimum Input-Output Voltage Differential vs. Load Current –8– REV. B ADR420/ADR421/ADR423/ADR425 2.5 2.0 –40 C 1.5 +25 C 1 V/DIV DIFFERENTIAL VOLTAGE – V +125 C 1.0 0.5 0 0 1 2 3 LOAD CURRENT – mA 4 5 TIME – 1s/DIV TPC 19. ADR423 Minimum Input-Output Voltage Differential vs. Load Current TPC 22. ADR421 Typical Noise Voltage 0.1 Hz to 10 Hz 2.5 DIFFERENTIAL VOLTAGE – V 2.0 –40 C +25 C 1.5 +125 C 1.0 0.5 0 0 1 2 3 LOAD CURRENT – mA 4 5 50 V/DIV TIME – 1s/DIV TPC 20. ADR425 Minimum Input-Output Voltage Differential vs. Load Current TPC 23. Typical Noise Voltage 10 Hz to 10 kHz 30 TEMPERATURE +25 C –40 C +125 C +25 C SAMPLE SIZE – 160 1k 25 20 VOLTAGE NOISE DENSITY FREQUENCY ADR425 ADR423 100 15 10 ADR420 ADR421 5 0 –100 –90 –80 –70 –60 –50 –40 –30 –20 –10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 MORE 10 10 100 1k FREQUENCY – Hz 10k DEVIATION – ppm TPC 21. ADR421 Typical Hysteresis TPC 24. Voltage Noise Density vs. Frequency REV. B –9– ADR420/ADR421/ADR423/ADR425 CBYPASS = 0 F 1mA LOAD LINE INTERRUPTION CL = 100nF VOUT VIN 500mV/DIV 1V/DIV LOAD OFF VOUT 500mV/DIV LOAD ON 2V/DIV TIME – 100 s/DIV TIME – 100 s/DIV TPC 25. ADR421 Line Transient Response TPC 28. ADR421 Load Transient Response CBYPASS = 0.1 F VIN LINE INTERRUPTION CIN = 0.01 F NO LOAD 500mV/DIV VOUT 2V/DIV VOUT 500mV/DIV VIN 2V/DIV TIME – 100 s/DIV TIME – 4 s/DIV TPC 26. ADR421 Line Transient Response TPC 29. ADR421 Turn-Off Response CL = 0 F VOUT 1mA LOAD CIN = 0.01 F NO LOAD 1V/DIV VOUT 2V/DIV LOAD OFF VIN 2V/DIV 2V/DIV LOAD ON TIME – 100 s/DIV TIME – 4 s/DIV TPC 27. ADR421 Load Transient Response TPC 30. ADR421 Turn-On Response –10– REV. B ADR420/ADR421/ADR423/ADR425 50 CLOAD = 0.01 F NO INPUT CAP 45 40 OUTPUT IMPEDANCE – VOUT 2V/DIV 35 30 25 20 15 10 5 ADR420 10 100 1k FREQUENCY – Hz 10k 100k ADR425 ADR423 ADR421 VIN 2V/DIV TIME – 4 s/DIV TPC 31. ADR421 Turn-Off Response TPC 34. Output Impedance vs. Frequency CLOAD = 0.01 F NO INPUT CAP –10 –20 RIPPLE REJECTION – dB VOUT 2V/DIV –30 –40 –50 –60 –70 –80 –90 10 100 1k 10k FREQUENCY – Hz 100k 1M VIN 2V/DIV TIME – 4 s/DIV TPC 32. ADR421 Turn-On Response TPC 35. Ripple Rejection vs. Frequency CBYPASS = 0.1 F RL = 500 CL = 0 VOUT 5V/DIV VIN 2V/DIV TIME – 100 s/DIV TPC 33. ADR421 Turn-On/Turn-Off Response REV. B –11– ADR420/ADR421/ADR423/ADR425 THEORY OF OPERATION Basic Voltage Reference Connections The ADR42x series of references uses a new reference generation technique known as XFET (eXtra implanted junction FET). This technique yields a reference with low supply current, good thermal hysteresis, and exceptionally low noise. The core of the XFET reference consists of two junction field-effect transistors (JFET), 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/°C. This slope is essentially constant 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 requiring less correction), resulting in much lower noise since most of the noise of a bandgap reference comes from the temperature compensation circuitry. Figure 1 shows the basic topology of the ADR42x series. The temperature correction term is provided by a current source with a value designed to be proportional to absolute temperature. The general equation is: VOUT = G × ( ∆VP − R1 × I PTAT ) (1) Voltage references, in general, require a bypass capacitor connected from V OUT t o GND. The circuit in Figure 2 illustrates the basic configuration for the ADR42x family of references. Other than a 0.1 µF capacitor at the output to help improve noise suppression, a large output capacitor at the output is not required for circuit stability. TP 1 VIN 10 F 2 8 TP NIC OUTPUT TRIM 0.1 F + ADR42x 7 0.1 F NIC 3 4 6 TOP VIEW (Not to Scale) 5 NIC = NO INTERNAL CONNECTION TP = TEST PIN (DO NOT CONNECT) Figure 2. Basic Voltage Reference Configuration Noise Performance The noise generated by the ADR42x family of references is typi cally less than 2 µV p-p over the 0.1 Hz to 10 Hz band for ADR420, ADR421, and ADR423. TPC 22 shows the 0.1 Hz to 10 Hz noise of the ADR421, which is only 1.75 µV 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 where G is the gain of the reciprocal of the divider ratio, ∆VP is the difference in pinch-off voltage between the two JFETs, and IPTAT is the positive temperature coefficient correction current. ADR42x are created by on-chip adjustment of R2 and R3 to achieve 2.048 V or 2.500 V at the reference output respectively. VIN I1 IPTAT I1 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. TPC 29 through TPC 33, inclusive, show the turn-on settling time for the ADR421. APPLICATIONS SECTION OUTPUT ADJUSTMENT ADR42x VOUT R2 * VP R1 R3 *EXTRA CHANNEL IMPLANT VOUT = G( VP – R1 IPTAT) GND The ADR42x trim terminal can be used to adjust the output voltage over a ± 0.5% range. This feature allows the system designer to trim system errors out by setting the reference to a voltage other than the nominal. This is also helpful if the part is used in a system at temperature to trim out any error. Adjustment of the output has negligible effect on the temperature performance of the device. To avoid degrading temperature coefficient, both the trimming potentiometer and the two resistors need to be low temperature coefficient types, preferably