1.25 V Micropower, Precision Shunt Voltage Reference ADR1581 PIN CONFIGURATION FEATURES Wide operating range: 60 μA to 10 mA Initial accuracy: ±0.12% maximum Temperature drift: ±50 ppm/°C maximum Output impedance: 0.5 Ω maximum Wideband noise (10 Hz to 10 kHz): 20 μV rms Operating temperature range: −40°C to +85°C High ESD rating 4 kV human body model 400 V machine model Compact, surface-mount SOT-23 package V+ 1 ADR1581 3 NC (OR V–) TOP VIEW NC = NO CONNECT 06672-001 V– 2 Figure 1. SOT-23 20 18 16 APPLICATIONS 14 QUANTITY The superior accuracy and stability of the ADR1581 is made possible by the precise matching and thermal tracking of onchip components. Proprietary curvature correction design techniques have been used to minimize the nonlinearities in the voltage output temperature characteristics. The ADR1581 is stable with any value of capacitive load. 8 4 2 0 –20 –10 0 10 TEMPERATURE DRIFT (ppm/°C) 20 Figure 2. Reverse Voltage Temperature Drift Distribution 100 90 80 70 QUANTITY The ADR1581 is a low cost, 2-terminal (shunt), precision band gap reference. It provides an accurate 1.250 V output for input currents between 60 μA and 10 mA. 10 6 GENERAL DESCRIPTION 1 12 06672-002 Portable, battery-powered equipment Cellular phones, notebook computers, PDAs, GPSs, and DMMs Computer workstations Suitable for use with a wide range of video RAMDACs Smart industrial transmitters PCMCIA cards Automotive 3 V/5 V, 8-bit to 12-bit data converters 60 50 40 30 20 10 0 –5 –4 –3 –2 –1 0 1 2 OUTPUT ERROR (mV) 3 4 5 06672-003 The low minimum operating current makes the ADR1581 ideal for use in battery-powered 3 V or 5 V systems. However, the wide operating current range means that the ADR1581 is extremely versatile and suitable for use in a wide variety of high current applications. Figure 3. Reverse Voltage Error Distribution The ADR1581 is available in two grades, A and B, both of which are provided in the SOT-23 package. Both grades are specified over the industrial temperature range of −40°C to +85°C. 1 Protected by U.S. Patent No. 5,969,657; other patents pending. Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2007 Analog Devices, Inc. All rights reserved. ADR1581 TABLE OF CONTENTS Features .............................................................................................. 1 Temperature Performance............................................................6 Applications....................................................................................... 1 Voltage Output Nonlinearity vs. Temperature ..........................7 General Description ......................................................................... 1 Reverse Voltage Hysteresis...........................................................7 Pin Configuration............................................................................. 1 Output Impedance vs. Frequency ...............................................8 Revision History ............................................................................... 2 Noise Performance and Reduction .............................................8 Specifications..................................................................................... 3 Turn-On Time ...............................................................................8 Absolute Maximum Ratings............................................................ 4 Transient Response .......................................................................9 ESD Caution.................................................................................. 4 Precision Micropower Low Dropout Reference .......................9 Typical Performance Characteristics ............................................. 5 Using the ADR1581 with 3 V Data Converters ..................... 10 Theory of Operation ........................................................................ 6 Outline Dimensions ....................................................................... 11 Applying the ADR1581................................................................ 6 Ordering Guide .......................................................................... 12 REVISION HISTORY 5/07—Revision 0: Initial Version Rev. 0 | Page 2 of 12 ADR1581 SPECIFICATIONS TA = 25°C, IIN = 100 μA, unless otherwise noted. Table 1. Parameter REVERSE VOLTAGE OUTPUT (SOT-23) REVERSE VOLTAGE TEMPERATURE DRIFT −40°C to +85°C MINIMUM OPERATING CURRENT, TMIN to TMAX REVERSE VOLTAGE CHANGE WITH REVERSE CURRENT 60 μA < IIN < 10 mA, TMIN to TMAX 60 μA < IIN < 1 mA, TMIN to TMAX DYNAMIC OUTPUT IMPEDANCE (∆VR/ΔIR) IIN = 1 mA ± 100 μA (f = 120 Hz) OUTPUT NOISE RMS Noise Voltage: 10 Hz to 10 kHz Low Frequency Noise Voltage: 0.1 Hz to 10 Hz TURN-ON SETTLING TIME TO 0.1% 1 OUTPUT VOLTAGE HYSTERESIS 2 TEMPERATURE RANGE Specified Performance, TMIN to TMAX Operating Range 3 1 2 3 Min 1.240 ADR1581A Typ Max 1.250 1.260 Min 1.2485 ADR1581B Typ Max 1.250 1.2515 100 60 Unit V 50 60 ppm/°C μA 2.5 0.8 6 2.5 0.8 6 mV mV 0.4 1 0.4 0.5 Ω 20 4.5 5 80 −40 −55 20 4.5 5 80 +85 +125 −40 −55 μV rms μV p-p μs μV +85 +125 Measured with a no load capacitor. Output hysteresis is defined as the change in the +25°C output voltage after a temperature excursion to −40°C, then to +85°C, and back to +25°C. The operating temperature range is defined as the temperature extremes at which the device continues to function. Parts may deviate from their specified performance. Rev. 0 | Page 3 of 12 °C °C ADR1581 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Reverse Current Forward Current Internal Power Dissipation1 SOT-23 (RT) Storage Temperature Range Operating Temperature Range ADR1581/RT Lead Temperature, Soldering Vapor Phase (60 sec) Infrared (15 sec) ESD Susceptibility2 Human Body Model Machine Model 1 2 Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Rating 25 mA 20 mA 0.3 W −65°C to +150°C −55°C to +125°C ESD CAUTION 215°C 220°C 4 kV 400 V Specification is for device (SOT-23 package) in free air at 25°C: θJA = 300°C/W. The human body model is a 100 pF capacitor discharged through 1.5 kΩ. For the machine model, a 200 pF capacitor is discharged directly into the device. Rev. 0 | Page 4 of 12 ADR1581 TYPICAL PERFORMANCE CHARACTERISTICS 100 1500 80 REVERSE CURRENT (µA) REVERSE VOLTAGE CHANGE (ppm) 2000 1000 20ppm/°C 500 0 5ppm/°C –500 60 40 +125°C –40°C 20 –1000 5 25 45 65 TEMPERATURE (°C) 85 105 125 0 7 0.6 0.8 1.0 REVERSE VOLTAGE (V) 1.2 1.4 100 1 6 –40°C 0.8 4 FORWARD VOLTAGE (µA) 5 +85°C 3 2 1 –40°C +25°C +25°C 0.6 +85°C 0.4 0.2 0 –1 0.01 0.10 1.00 REVERSE CURRENT (mA) 10 0 0.01 06672-005 REVERSE VOLTAGE CHANGE (mV) 0.4 Figure 7. Reverse Current vs. Reverse Voltage Figure 4. Output Drift for Different Temperature Characteristics 600 400 10 100 1k 10k FREQUENCY (Hz) 100k 1M 06672-006 200 1.0 0.1 1 10 FORWARD CURRENT (mA) Figure 8. Forward Voltage vs. Forward Current Figure 5. Output Voltage Error vs. Reverse Current NOISE VOLTAGE (nV/ Hz) 0.2 06672-007 –15 06672-004 –35 0 06672-008 +25°C –1500 –55 Figure 6. Noise Spectral Density Rev. 0 | Page 5 of 12 ADR1581 THEORY OF OPERATION Figure 11 shows a typical connection of the ADR1581BRT operating at a minimum of 100 μA. This connection can provide ±1 mA to the load while accommodating ±10% power supply variations. VS RS IR + IL IL VR IR 06672-010 VOUT Figure 10. Typical Connection Diagram +5V(+3V) ±10% RS 2.94kΩ (1.30kΩ) VR VOUT 06672-011 The ADR1581 uses the band gap concept to produce a stable, low temperature coefficient voltage reference suitable for high accuracy data acquisition components and systems. The device makes use of the underlying physical nature of a silicon transistor base emitter voltage in the forward-biased operating region. All such transistors have an approximately −2 mV/°C temperature coefficient, which is unsuitable for use directly as a low TC reference; however, extrapolation of the temperature characteristic of any one of these devices to absolute zero (with collector current proportional to absolute temperature) reveals that its VBE goes to approximately the silicon band gap voltage. Therefore, if a voltage could be developed with an opposing temperature coefficient to sum with VBE, a zero TC reference would result. The ADR1581 circuit in Figure 9 provides such a compensating voltage, V1, by driving two transistors at different current densities and amplifying the resultant VBE difference (ΔVBE), which has a positive TC. The sum of VBE and V1 provides a stable voltage reference. V+ Figure 11. Typical Connection Diagram TEMPERATURE PERFORMANCE V1 The ADR1581 is designed for reference applications where stable temperature performance is important. Extensive temperature testing and characterization ensure that the device’s performance is maintained over the specified temperature range. VBE V– 06672-009 ΔVBE Figure 9. Schematic Diagram APPLYING THE ADR1581 The ADR1581 is simple to use in virtually all applications. To operate the ADR1581 as a conventional shunt regulator (see Figure 10), an external series resistor is connected between the supply voltage and the ADR1581. For a given supply voltage, the series resistor, RS, determines the reverse current flowing through the ADR1581. The value of RS must be chosen to accommodate the expected variations of the supply voltage (VS), load current (IL), and the ADR1581 reverse voltage (VR) while maintaining an acceptable reverse current (IR) through the ADR1581. The minimum value for RS should be chosen when VS is at its minimum and IL and VR are at their maximum while maintaining the minimum acceptable reverse current. The value of RS should be large enough to limit IR to 10 mA when VS is at its maximum and IL and VR are at their minimum. Some confusion exists in the area of defining and specifying reference voltage error over temperature. Historically, references have been characterized using a maximum deviation per degree Celsius, for example, 50 ppm/°C. However, because of nonlinearities in temperature characteristics that originated in standard Zener references (such as S type characteristics), most manufacturers now use a maximum limit error band approach to specify devices. This technique involves the measurement of the output at three or more temperatures to guarantee that the voltage falls within the given error band. The proprietary curvature correction design techniques used to minimize the ADR1581 nonlinearities allow the temperature performance to be guaranteed using the maximum deviation method. This method is more useful to a designer than one that simply guarantees the maximum error band over the entire temperature change. Figure 12 shows a typical output voltage drift for the ADR1581 and illustrates the methodology. The maximum slope of the two diagonals drawn from the initial output value at +25°C to the output values at +85°C and −40°C determines the performance grade of the device. For a given grade of the ADR1581, the designer can easily determine the maximum total error from the initial tolerance plus the temperature variation. The equation for selecting RS is as follows: RS = (VS − VR)/(IR + IL) Rev. 0 | Page 6 of 12 ADR1581 1.2508 600 (VMAX – VO) 1.2506 SLOPE = TC = (+85°C – +25°C) × 1.250V × 10 –6 OUTPUT VOLTAGE (V) RESIDUAL DRIFT ERROR (ppm) VMAX 1.2504 1.2502 1.2500 VO 1.2498 1.2496 1.2494 1.2492 SLOPE = TC = (VMIN – VO) (–40°C – +25°C) × 1.250V × 10 –6 500 400 300 200 100 VMIN –15 5 25 45 65 85 TEMPERATURE (°C) 105 125 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) Figure 12. Output Voltage vs. Temperature Figure 13. Residual Drift Error For example, the ADR1581BRT initial tolerance is ±1.5 mV; a ±50 ppm/°C temperature coefficient corresponds to an error band of ±4.1 mV (50 × 10−6 × 1.250 V × 65°C). Therefore, the unit is guaranteed to be 1.250 V ± 5.6 mV over the operating temperature range. Duplication of these results requires a combination of high accuracy and stable temperature control in a test system. Evaluation of the ADR1581 produces curves similar to those in Figure 4 and Figure 12. REVERSE VOLTAGE HYSTERESIS A major requirement for high performance industrial equipment manufacturers is a consistent output voltage at nominal temperature following operation over the operating temperature range. This characteristic is generated by measuring the difference between the output voltage at +25°C after operating at +85°C and the output voltage at +25°C after operating at −40°C. Figure 14 displays the hysteresis associated with the ADR1581. This characteristic exists in all references and has been minimized in the ADR1581. VOLTAGE OUTPUT NONLINEARITY VS. TEMPERATURE 40 Rev. 0 | Page 7 of 12 35 30 QUANTITY When a reference is used with data converters, it is important to understand how temperature drift affects the overall converter performance. The nonlinearity of the reference output drift represents additional error that is not easily calibrated out of the system. The usual way of showing the reference output drift is to plot the reference voltage vs. temperature (see Figure 12). An alternative method is to draw a straight line between the temperature endpoints and measure the deviation of the output from the straight line. This shows the same data in a different format. This characteristic (see Figure 13) is generated by normalizing the measured drift characteristic to the endpoint average drift. The residual drift error of approximately 500 ppm shows that the ADR1581 is compatible with systems that require 10-bit accurate temperature performance. 25 20 15 10 5 0 –400 –300 –200 –100 0 100 200 300 HYSTERESIS VOLTAGE (µV) Figure 14. Reverse Voltage Hysteresis Distribution 400 06672-014 –35 06672-012 1.2488 –55 06672-013 1.2490 ADR1581 OUTPUT IMPEDANCE VS. FREQUENCY 40µV/DIV Understanding the effect of the reverse dynamic output impedance in a practical application is important to successfully applying the ADR1581. A voltage divider is formed by the ADR1581 output impedance and the external source impedance. When an external source resistor of about 30 kΩ (IR = 100 μA) is used, 1% of the noise from a 100 kHz switching power supply is developed at the output of the ADR1581. Figure 15 shows how a 1 μF load capacitor connected directly across the ADR1581 reduces the effect of power supply noise to less than 0.01%. 21µV rms (a) 20µV/DIV 6.5µV rms, t = 0.2ms (b) (c) 10ms/DIV 1k 06672-017 2.90µV rms, t = 960ms 10µV/DIV OUTPUT IMPEDANCE (Ω) Figure 17. Total RMS Noise 100 TURN-ON TIME CL = 0 Many low power instrument manufacturers are becoming increasingly concerned with the turn-on characteristics of the components in their systems. Fast turn-on components often enable the end user to keep power off when not needed, and yet those components respond quickly when the power is turned on for operation. Figure 18 displays the turn-on characteristics of the ADR1581. 10 ΔIR = 0.1IR IR = 100µA CL = 1µF 1 0.1 10 100 1k 10k 100k FREQUENCY (Hz) 1M 06672-015 IR = 1mA Figure 15. Output Impedance vs. Frequency NOISE PERFORMANCE AND REDUCTION The noise generated by the ADR1581 is typically less than 5 μV p-p over the 0.1 Hz to 10 Hz band. Figure 16 shows the 0.1 Hz to 10 Hz noise of a typical ADR1581. Noise in a 10 Hz to 10 kHz bandwidth is approximately 20 μV rms (see Figure 17a). If further noise reduction is desired, a one-pole low-pass filter can be added between the output pin and ground. A time constant of 0.2 ms has a −3 dB point at about 800 Hz and reduces the high frequency noise to about 6.5 μV rms (see Figure 17b). A time constant of 960 ms has a −3 dB point at 165 Hz and reduces the high frequency noise to about 2.9 μV rms (see Figure 17c). Upon application of power (cold start), the time required for the output voltage to reach its final value within a specified error is the turn-on settling time. Two components normally associated with this are time for active circuits to settle and time for thermal gradients on the chip to stabilize. This characteristic is generated from cold start operation and represents the true turn-on waveform after power-up. Figure 20 shows both the coarse and fine turn-on settling characteristics of the device; the total settling time to within 1.0 mV is about 6 μs, and there is no long thermal tail when the horizontal scale is expanded to 2 ms/div. 2.4V VIN 0V CL = 200pF 250mV/DIV 1µV/DIV 06672-018 4.48µV p-p 5µs/DIV Figure 18. Turn-On Response Time RL RS = 11.5kΩ 06672-016 TIME (1s/DIV) VR CL VOUT – Figure 19. Turn-On, Settling, and Transient Test Circuit Figure 16. 0.1 Hz to 10 Hz Voltage Noise Rev. 0 | Page 8 of 12 006672-010 + VIN ADR1581 Output turn-on time is modified when an external noise-reduction filter is used. When present, the time constant of the filter dominates the overall settling. 2.4V VIN 0V OUTPUT ERROR 1mV/DIV, 2µs/DIV Attempts to drive a large capacitive load (in excess of 1000 pF) may result in ringing, as shown in the step response (see Figure 22). This is due to the additional poles formed by the load capacitance and the output impedance of the reference. A recommended method of driving capacitive loads of this magnitude is shown in Figure 19. A resistor isolates the capacitive load from the output stage, whereas the capacitor provides a single-pole low-pass filter and lowers the output noise. 2.0V VIN OUTPUT 0.5mV/DIV, 2ms/DIV 06672-020 1.8V Figure 20. Turn-On Settling CL = 0.01µF Many ADCs and DACs present transient current loads to the reference. Poor reference response can degrade the converter’s performance. Figure 21 displays both the coarse and fine settling characteristics of the device to load transients of ±50 μA. 20mV/DIV 10mV/DIV Figure 22. Transient Response with Capacitive Load PRECISION MICROPOWER LOW DROPOUT REFERENCE The circuit in Figure 23 provides an ideal solution for creating a stable voltage reference with low standby power consumption, low input/output dropout capability, and minimum noise output. The amplifier both buffers and optionally scales up the ADR1581 output voltage. Output voltages as high as 2.1 V can supply 1 mA of load current. A one-pole filter connected between the ADR1581 and the OP193 input can be used to achieve low output noise. The nominal quiescent power consumption is 250 μW. 1mV/DIV IR = 150µA + 50µA STEP (a) (b) 3V IR = 150µA – 50µA STEP 1mV/DIV 1µs/DIV 06672-021 28.7kΩ 20mV/DIV 50µs/DIV 06672-022 TRANSIENT RESPONSE 205Ω OP193 4.7µF Figure 21. Transient Settling ADR1581 R3 R2 06672-023 Figure 21a shows the settling characteristics of the device for an increased reverse current of 50 μA. Figure 21b shows the response when the reverse current is decreased by 50 μA. The transients settle to 1 mV in about 3 μs. VOUT = 1.250V OR VOUT = 1.250 (1 + R2/R3) Figure 23. Micropower Buffered Reference Rev. 0 | Page 9 of 12 ADR1581 USING THE ADR1581 WITH 3 V DATA CONVERTERS The ADR1581 low output drift (50 ppm/°C) and compact subminiature SOT-23 package make it ideally suited for today’s high performance converters in space-critical applications. One family of ADCs for which the ADR1581 is well suited is the AD7714-3 and AD7715-3. The AD7714/AD7715 are chargebalancing (∑-Δ) ADCs 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. Figure 24 shows the ADR1581 connected to the AD7714/AD7715 for 3 V operation. 3.3V REF IN(–) CREF (3pF TO 8pF) IOUT2 AGND A1 VOUT A1: OP295 AD822 OP2283 DGND HIGH IMPEDANCE >1GΩ SWITCHING FREQUENCY DEPENDS ON fCLKIN DAC AD7943 AD7714-3/AD7715-3 RSW 5kΩ (TYP) VREF 3.3V 29.4kΩ A1 ADR1581 Figure 24. Reference Circuit for the AD7714-3/AD7715-3 SIGNAL GROUND Figure 25. Single-Supply System Rev. 0 | Page 10 of 12 06672-025 REF IN(+) C1 IOUT1 06672-024 28.7kΩ RFB VDD VIN 3V ADR1581 The ADR1581 is ideal for creating the reference level to use with 12-bit multiplying DACs, such as the AD7943, AD7945, and AD7948. In the single-supply bias mode (see Figure 25), the impedance seen looking into the IOUT2 terminal changes with DAC code. If the ADR1581 drives IOUT2 and AGND directly, less than 0.2 LSBs of additional linearity error results. The buffer amp eliminates linearity degradation resulting from variations in the reference level. ADR1581 OUTLINE DIMENSIONS 3.04 2.90 2.80 1.40 1.30 1.20 3 1 2.64 2.10 2 PIN 1 0.95 BSC 1.90 BSC 1.12 0.89 0.10 0.01 0.50 0.30 SEATING PLANE 0.20 0.08 0.60 0.50 0.40 COMPLIANT TO JEDEC STANDARDS TO-236-AB Figure 26. 3-Lead Small Outline Transistor Package [SOT-23-3] (RT-3) Dimensions shown in millimeters 1.55 1.50 1.45 2.05 2.00 1.95 8.30 8.00 7.70 1.10 1.00 0.90 1.10 1.00 0.90 3.55 3.50 3.45 3.20 3.10 2.90 1.00 MIN 2.80 2.70 2.60 7” REEL 100.00 OR 13” REEL 330.00 0.35 0.30 0.25 1.50 MIN 20.20 MIN 14.40 MIN 7” REEL 50.00 MIN OR 13” REEL 100.00 MIN 13.20 13.00 12.80 0.75 MIN 9.90 8.40 6.90 DIRECTION OF UNREELING Figure 27. Tape and Reel Dimensions (RT-3) Dimensions shown in millimeters Rev. 0 | Page 11 of 12 053006-0 4.10 4.00 3.90 ADR1581 ORDERING GUIDE Model ADR1581ARTZ-REEL7 1 ADR1581ARTZ-R21 ADR1581BRTZ-REEL71 ADR1581BRTZ-R21 1 Temperature Range −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C Initial Output Error 10 mV 10 mV 1 mV 1 mV Temperature Coefficient 100 ppm/°C 100 ppm/°C 50 ppm/°C 50 ppm/°C Z = RoHS Compliant Part. ©2007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06672-0-5/07(0) Rev. 0 | Page 12 of 12 Package Description 3-Lead SOT-23-3 3-Lead SOT-23-3 3-Lead SOT-23-3 3-Lead SOT-23-3 Package Option RT-3 RT-3 RT-3 RT-3 Branding R2M R2M R2K R2K