Precision Low Power 2.048 V SOT-23 Voltage Reference ADR370 FEATURES APPLICATIONS PIN CONFIGURATION VIN 1 ADR370 VOUT 3 GND 03432-001 Initial accuracy: 4 mV maximum Initial accuracy error: 0.2% Low TCVO 50 ppm/C maximum from -40C to +125C 30 ppm/C maximum from +25C to +70C Load regulation: 400 V/mA, 100 ppm/mA Line regulation: 25 V/V, 20 ppm/V Wide operating range: VIN = 2.3 V to 15 V Low power: 72 A maximum High output sink/source current: 5 mA minimum Wide temperature range: -40C to +125C Tiny 3-lead SOT-23 package with standard pin configuration 2 Figure 1. 3-Lead SOT-23 Table 1. ADR370 Products Products ADR370BRT-REEL7 ADR370ART-REEL7 Output Voltage (V) 2.048 2.048 Initial Accuracy (mV) (%) 4 0.2 10 0.5 Temperature Coefficient (ppm/C) 50 100 Battery-powered instrumentation Portable medical instruments Data acquisition systems Industrial process control systems Automotive GENERAL DESCRIPTION The ADR370 is a low cost, 3-terminal (series) band gap voltage reference featuring high accuracy, high stability, and low power consumption packaged in a tiny 3-lead SOT-23 package. Precise matching and thermal tracking of on-chip components, as well as patented temperature drift curvature correction design techniques, have been employed to ensure that the ADR370 provides an accurate 2.048 V output. This micropowered, low dropout voltage device sources or sinks up to 5 mA of load current while providing a stable 2.048 V output. The compact footprint, high accuracy, and operating range of 2.3 V to 15 V make the ADR370 ideal for use in 3 V and 5 V systems where there can be wide variations in supply voltage and a need to minimize power dissipation. The ADR370 is offered in A and B grades; all devices are specified over the extended industrial range of -40C to +125C. Rev. C 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 (c)2003-2007 Analog Devices, Inc. All rights reserved. ADR370 TABLE OF CONTENTS Features .............................................................................................. 1 Theory of Operation .........................................................................8 Applications ....................................................................................... 1 Applying the ADR370...................................................................8 Pin Configuration ............................................................................. 1 Applications Information .................................................................9 General Description ......................................................................... 1 Low Cost Negative Reference ......................................................9 Revision History ............................................................................... 2 Precision Negative Reference .......................................................9 Specifications..................................................................................... 3 Low Cost Current Source .............................................................9 Electrical Characteristics ............................................................. 3 Precision Current Source with Adjustable Output ...................9 Absolute Maximum Ratings............................................................ 4 12-Bit Precision Programmable Current Source ................... 10 Thermal Resistance ...................................................................... 4 Precision Boosted Output Regulator ....................................... 10 ESD Caution .................................................................................. 4 Outline Dimensions ....................................................................... 11 Typical Performance Characteristics ............................................. 5 Ordering Guide .......................................................................... 11 Terminology ...................................................................................... 7 REVISION HISTORY 12/07--Rev. B to Rev. C Changes to Line Regulation Specification..................................... 3 9/07--Rev. A to Rev. B Updated Format .................................................................. Universal Changes to Table 2 ............................................................................ 3 Changes to Ordering Guide .......................................................... 11 Updated Outline Dimensions ....................................................... 11 7/03--Rev. 0 to Rev. A Changes to Features.......................................................................... 1 Changes to Table I ............................................................................ 1 Changes to Electrical Characteristics ............................................ 2 Changes to Absolute Maximum Ratings ....................................... 3 Changes to Ordering Guide ............................................................ 3 Changes to Parameter Definitions ................................................. 6 Updated Outline Dimensions ......................................................... 9 Rev. C | Page 2 of 12 ADR370 SPECIFICATIONS ELECTRICAL CHARACTERISTICS TA = TMIN to TMAX, VIN = 5 V, unless otherwise noted. Table 2. Parameter OUTPUT VOLTAGE (@ 25C) INITIAL ACCURACY ERROR A Grade Symbol VO VOERR Conditions Typ 2.048 -10 -0.5 -4 -0.2 B Grade OUTPUT VOLTAGE TEMPERATURE DRIFT 1 A Grade B Grade TCVO SUPPLY HEADROOM LOAD REGULATION VIN - VOUT TA = -40C to +125C TA = -40C to +125C TA = 25C to 70C LINE REGULATION RIPPLE REJECTION QUIESCENT CURRENT SHORT-CIRCUIT CURRENT TO GROUND NOISE VOLTAGE (@ 25C) VOUT/VIN TURN-ON SETTLING TIME LONG-TERM STABILITY OUTPUT VOLTAGE HYSTERESIS TEMPERATURE RANGE CL = 0.2 F 1 Min 2.044 Max 2.052 Unit V +10 +0.5 +4 +0.2 mV % mV % 100 50 30 ppm/C ppm/C ppm/C mV mV/mA mV/mA mV/mA ppm/V 200 0 mA < IOUT < 5 mA @ 25C -3 mA < IOUT < 0 mA @ 25C -0.1 mA < IOUT < +0.1 mA VOUT + 200 mV < VIN < 15 V IOUT = 0 mA VIN = 5 V 100 mV (f = 120 Hz) +0.400 +0.600 +4.75 20 80 72 15 0.1 Hz to 10 Hz 10 Hz to 10 kHz 70 50 100 1000 hours @ 25C 100 115 -40 Guaranteed by characterization. Rev. C | Page 3 of 12 +125 dB A mA V p-p V rms s ppm/1000 hrs ppm C ADR370 ABSOLUTE MAXIMUM RATINGS Ratings at 25C, unless otherwise noted. THERMAL RESISTANCE Table 3. JA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. Parameter Supply Voltage Storage Temperature Range Operating Temperature Range Lead Temperature Soldering, 60 sec Infrared, 15 sec Rating 18 V -65C to +125C -40C to +125C Table 4. Package Type 3-Lead SOT-23 (RT) 215C 220C ESD CAUTION 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. Rev. C | Page 4 of 12 JA 220 JC 102 Unit C/W ADR370 TYPICAL PERFORMANCE CHARACTERISTICS 12 6 10 4 LINE REGULATION (ppm/V) VIN = 5V TO 15V 8 -40C 4 +125C 2 0 +25C -4 -4 -3 -2 -1 0 1 2 3 4 -2 -4 -6 -8 03432-002 -2 0 -10 -40 5 LOAD (mA) 03432-005 VO (mV) 6 2 45 125 TEMPERATURE (C) Figure 2. Load Regulation vs. Load Current Figure 5. Line Regulation vs. Temperature 2.048 2.046 VOLTAGE (10V/DIV) OUTPUT VOLTAGE (V) VIN = 5V 2.044 2.042 VIN = 15V 2.040 03432-003 2.036 -40 03432-006 2.038 125 45 TIME (0.1s/DIV) TEMPERATURE (C) Figure 6. Voltage Noise 0.1 Hz to 10 Hz Figure 3. Output Voltage vs. Temperature 80 VOLTAGE (200V/DIV) VIN = 15V 60 VIN = 5V 50 40 20 -40 03432-007 30 03432-004 SUPPLY CURRENT (A) 70 45 125 TIME (0.1s/DIV) TEMPERATURE (C) Figure 7. Voltage Noise 10 Hz to 100 kHz Figure 4. Supply Current vs. Temperature Rev. C | Page 5 of 12 ADR370 CL = 0.1F CBY = 0.1F CL = 0.22F VOUT = 1V/DIV VOLTAGE (V) VOLTAGE (V) VIN = 1V/DIV 03432-010 VOUT = 1V/DIV 03432-008 VIN = 5V/DIV TIME (100s/DIV) TIME (100s/DIV) Figure 8. Turn-On Response Figure 10. Line Transient Response CBY = 0.1F CL = 0.1F RLOAD = 1k VOLTAGE (V) VOLTAGE (V) VOUT = 20mV/DIV VOUT = 1V/DIV VIN = 2V/DIV 03432-009 03432-011 VIN = 5V/DIV TIME (100ms/DIV) TIME (100s/DIV) Figure 11. Load Transient Response Figure 9. Turn-Off Response Rev. C | Page 6 of 12 ADR370 TERMINOLOGY Temperature Coefficient Temperature coefficient is the change of output voltage with respect to operating temperature changes, normalized by the output voltage at 25C. This parameter is expressed in ppm/C and can be determined by the following equation: VO (T2 ) - VO (T1 ) ppm = x 10 6 TCVO C VO (25 C ) x (T2 - T1 ) Long-Term Stability Long-term stability is the typical shift of output voltage at 25C on a sample of parts subjected to a test of 1000 hours at 25C. VO = VO (t 1 ) - VO (t 2 ) VO [ppm ] = (1) VO (t 1 ) - VO (t 2 ) x 10 6 VO (t 1 ) (2) where: VO(t1) = VO at 25C at Time 0. VO(t2) = VO at 25C after 1000 hours operation at 25C. where: VO(25C) = VO at 25C. VO(T1) = VO at Temperature 1. VO(T2) = VO at Temperature 2. Line Regulation Line regulation is the change in output voltage due to a specified change in input voltage. This parameter accounts for 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 Load regulation is the change in output voltage due to a specified change in load current. This parameter accounts for 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. Thermal Hysteresis Thermal hysteresis is defined as the change of output voltage after the device is cycled through temperature from +25C to -40C to +125C and back to +25C. 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 ) x 10 6 (3) where: VO(25C) = VO at 25C. VO_TC = VO at 25C after temperature cycle of +25C to -40C to +125C and back to +25C. Rev. C | Page 7 of 12 ADR370 THEORY OF OPERATION APPLYING THE ADR370 To achieve the specified performance, two external components should be used in conjunction with the ADR370: a 4.7 F capacitor and a 1 F capacitor. The 4.7 F capacitor should be applied to the input, and the 1 F capacitor should be applied to the output. Figure 13 shows the ADR370 with both the input and output capacitors attached. For further transient response optimization, an additional 0.1 F capacitor in parallel with the 4.7 F input capacitor can be used. A 1 F output capacitor provides stable performance for all loading conditions. The ADR370 can, however, operate under low (-100 A < IOUT < +100 A) current conditions with just a 0.2 F output capacitor and a 1 F input capacitor. CIN 4.7F COUT 1F VIN R4 ADR370 GND VOUT Figure 13. Typical Connection Diagram R3 VOUT R5 VDS R2 V1 GND 03432-012 R6 R1 VIN 03432-013 The ADR370 uses the band gap concept to produce a stable, low temperature coefficient voltage reference suitable for high accuracy data acquisition components and systems. This device makes use of the underlying temperature characteristics of a silicon transistor's base-emitter voltage (VBE) in the forwardbiased operating region. Under this condition, all such transistors have a -2 mV/C temperature coefficient (TC) and a VBE that, when extrapolated to absolute zero, 0 K, (with collector current proportional to absolute temperature), approximate the silicon band gap voltage. By summing a voltage that has an equal and opposite temperature coefficient of 2 mV/C with a VBE of a forward-biased transistor, an almost zero TC reference can be developed. The simplified circuit diagram in Figure 12 shows how a compensating voltage, V1, is achieved by driving two transistors at different current densities and amplifying the resulting VBE difference (VBE, which has a positive TC). The sum (VBG) of VBE and V1 is then buffered and amplified to produce a stable reference voltage of 2.048 V at the output. Figure 12. Simplified Schematic Rev. C | Page 8 of 12 ADR370 APPLICATIONS INFORMATION VL + 2.5V < VDD < VL + 12V LOW COST NEGATIVE REFERENCE ADR370 A low cost negative reference can be obtained by leveraging the current sinking capability of the ADR370. By simply tying the VOUT terminal to ground and adding a bias resistor (RSET) to the GND pin of the device, a negative voltage reference can be obtained as shown in Figure 14. RSET should be chosen such that ISET remains between 1 mA and 5 mA. VIN VOUT RSET GND ISET = 2.048V RSET VL Iq = 65A RL IL 03432-016 VDD ADR370 Figure 16. Low Cost Current Source VOUT VIN PRECISION CURRENT SOURCE WITH ADJUSTABLE OUTPUT GND -VREF A precision current source can be implemented with the circuit shown in Figure 17. By adding a mechanical or digital potentiometer, this circuit becomes an adjustable current source. If a digital potentiometer such as the AD5201 is used, the load current is simply the voltage across Terminal B-to-Terminal W of the digital potentiometer divided by RSET. ISET 03432-014 RSET VSS Figure 14. Low Cost Negative Reference PRECISION NEGATIVE REFERENCE Without using any matching resistors, a precision negative reference can be obtained using the configuration shown in Figure 15. The voltage difference between VOUT and GND of the ADR370 is 2.048 V. Because VOUT is at virtual ground, U2 closes the loop by forcing the GND pin to be the negative reference node. U2 should be a low offset voltage precision op amp, such as the OP1177. IL = VREF x D RSET x 256 (5) where D is the decimal equivalent of the digital potentiometer input code. 12V ADR370 0V TO (2.048V + VL) U1 VIN VOUT 2.3V TO 12V B ADR370 VIN GND AD5201 W A VOUT RSET +15V GND +12V U2 -VREF OP1177 VL -12V RL IL 03432-017 -15V -2.048V TO VL 03432-015 OP1177 Figure 15. Precision Negative Reference LOW COST CURRENT SOURCE Figure 17. Programmable 0 mA to 5 mA Current Source Figure 16 illustrates how a simple, low cost current source can be configured using the ADR370. The load current, IL, is simply the sum of ISET and the quiescent current, Iq. ISET is simply the reference voltage generated by the ADR370 divided by RSET. I SET = 2.048 V RSET To optimize the resolution of this circuit, dual-supply op amps should be used because the ground potential of the ADR370 can swing from -2.048 V at zero scale to VL at full scale of the potentiometer setting. (4) The quiescent current, Iq, varies slightly with load. The variation in Iq limits the use of this circuit to general-purpose applications. Rev. C | Page 9 of 12 ADR370 12-BIT PRECISION PROGRAMMABLE CURRENT SOURCE PRECISION BOOSTED OUTPUT REGULATOR A precision voltage output with boosted current can be realized with the circuit shown in Figure 19. In this circuit, VOUT is maintained by the ADR370 at 2.048 V. By replacing the potentiometer in Figure 17 with a 12-bit precision DAC, such as the AD5322, a higher precision programmable current source can be achieved. Figure 18 illustrates the implementation of this circuit. The load current can be determined with the following equation: IL = VREF (1 - D ) R SET x 4096 The ADR370 sources a maximum of 5 mA if the load current (IL) is more than 5 mA and if the current is furnished by the transistor (Q1) and the input voltage supply (VDD). 4V TO 12V VDD (6) R1 10k The compliance voltage should be kept low so that the supply voltage to U2, between VDD and GND, does not fall below 2.5 V. 2N3906 Q1 U1 +5V ADR370 ADR370 VIN VOUT VREF (1 - D2/N) U2 GND GND VREF +5V VOUT AD5322 VOUT VDD RL IL 03432-019 VIN RSET +5V GND 2 U3 1 OP1177 TOL 0.05% V+ V- 3 VL 11 RL IL 03432-018 -5V Figure 18. 12-Bit Programmable Current Source Figure 19. Precision Boosted Output Regulator Q1 is turned on to regulate current as needed. R1 is required to bias the base of Q1 and must be large enough to comply with the supply current requirements of the ADR370. The supply voltage can be as low as 4 V. The maximum current output of this circuit is limited by the power dissipation of the bipolar transistor, Q1. PDISS = (VDD - 2.048) x IL (7) When using the 2N3906 PNP transistor shown in Figure 19, a 4 V power supply (RL) should be chosen so that a maximum of 100 mA is drawn from the circuit, which limits the power dissipation of Q1 to ~200 mW. Rev. C | Page 10 of 12 ADR370 OUTLINE DIMENSIONS 1.55 1.50 1.45 1.10 1.00 0.90 2.05 2.00 1.95 8.30 8.00 7.70 1.00 MIN 0.35 0.30 0.25 14.40 MIN 1.50 MIN 2.80 2.70 2.60 3.55 3.50 3.45 3.20 3.10 2.90 7" REEL 100.00 OR 13" REEL 330.00 1.10 1.00 0.90 7" REEL 50.00 MIN OR 13" REEL 100.00 MIN 13.20 13.00 12.80 20.20 MIN 0.75 MIN 9.90 8.40 6.90 DIRECTION OF UNREELING 053006-0 4.10 4.00 3.90 Figure 20. SOT-23-3 Tape and Reel Outline Dimensions Dimensions shown in millimeters 3.04 2.80 1.40 1.20 2.64 2.10 3 1 2 0.60 0.45 1.03 0.89 2.05 1.78 1.12 0.89 0.100 0.013 0.180 0.085 0.51 0.37 0.55 REF COMPLIANT TO JEDEC STANDARDS TO-236-AB 092707-A SEATING PLANE Figure 21. 3-Lead Small Outline Transistor Package [SOT-23-3] (RT-3) Dimensions shown in millimeters ORDERING GUIDE Model ADR370ART-R2 ADR370ART-REEL7 ADR370ARTZ-REEL7 1 ADR370BRT-R2 ADR370BRT-REEL7 ADR370BRTZ-R21 ADR370BRTZ-REEL71 1 Output Voltage (V) 2.048 2.048 2.048 2.048 2.048 2.048 2.048 Initial Accuracy (mV) (%) 10 0.5 10 0.5 10 0.5 4 0.5 4 0.2 4 0.5 4 0.2 Temperature Coefficient (ppm/C) 100 100 100 50 50 50 50 Temperature Range -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C Z = RoHS Compliant Part. Rev. C | Page 11 of 12 Package Description 3-Lead SOT-23-3 3-Lead SOT-23-3 3-Lead SOT-23-3 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 RT-3 RT-3 RT-3 Ordering Quantity 250 3,000 3,000 250 3,000 250 3,000 Branding RPA RPA L26 RPB RPB L27 L27 ADR370 NOTES (c)2003-2007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D03432-0-12/07(C) Rev. C | Page 12 of 12