Low Noise Micropower 2.5 V and 4.096 V Precision Voltage References ADR291/ADR292 CONNECTION DIAGRAMS Supply range 2.8 V to 15 V, ADR291 4.4 V to 15 V, ADR292 Supply current: 15 μA maximum Low noise: 8 μV and 12 μV p-p (0.1 Hz to 10 Hz) High output current: 5 mA Temperature range: −40°C to +125°C Pin-compatible with REF02/REF19x NC 1 VIN 2 NC 3 ADR291/ ADR292 8 NC 7 NC 6 VOUT TOP VIEW GND 4 (Not to Scale) 5 NC NC = NO CONNECT 00163-001 FEATURES APPLICATIONS Portable instrumentation Precision reference for 3 V and 5 V systems Analog-to-digital and digital-to-analog converter reference Solar-powered applications Loop-current-powered instruments NC 1 VIN 2 NC 3 GND 4 ADR291/ ADR292 TOP VIEW (Not to Scale) 8 NC 7 NC 6 VOUT 5 NC NC = NO CONNECT 00163-002 Figure 1. 8-Lead SOIC (R-8) Figure 2. 8-Lead TSSOP (RU-8) GND VOUT 3 2 1 VIN TOP VIEW (Not to Scale) 00163-003 ADR291 Figure 3. 3-Lead TO-92 (T-3) GENERAL DESCRIPTION The ADR291 and ADR292 are low noise, micropower precision voltage references that use an XFET® reference circuit. The new XFET architecture offers significant performance improvements over traditional band gap and buried Zener-based references. Improvements include one quarter the voltage noise output of band gap references operating at the same current, very low and ultralinear temperature drift, low thermal hysteresis, and excellent long-term stability. The ADR291/ADR292 family is a series of voltage references providing stable and accurate output voltages from supplies as low as 2.8 V for the ADR291. Output voltage options are 2.5 V and 4.096 V for the ADR291 and ADR292, respectively. Quiescent current is only 12 μA, 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 maximum for the ADR291, and ±3 mV, ±4 mV, and ±6 mV maximum for the ADR292. Temperature coefficients for the three grades are 8 ppm/°C, 15 ppm/°C, and 25 ppm/°C maximum, 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 ADR291 and ADR292 references are specified over the extended industrial temperature range of −40°C to +125°C. Devices are available in the 8-lead SOIC, 8-lead TSSOP, and 3-lead TO-92 packages. Table 1. ADR291/ADR292 Product Part No. ADR291 ADR292 Output Voltage (V) 2.500 4.096 Initial Accuracy (±%) 0.08, 0.12, 0.24 0.07, 0.10, 0.15 Temperature Coefficient (ppm/°C) Max 8, 15, 25 8, 15, 25 Rev. F 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. 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ADR291/ADR292 TABLE OF CONTENTS Features .............................................................................................. 1 Theory of Operation ...................................................................... 13 Applications ....................................................................................... 1 Device Power Dissipation Considerations .............................. 13 Connection Diagrams ...................................................................... 1 Basic Voltage Reference Connections ..................................... 13 General Description ......................................................................... 1 Noise Performance ..................................................................... 13 Revision History ............................................................................... 2 Turn-On Time ............................................................................ 13 Specifications..................................................................................... 3 Applications Information .............................................................. 14 ADR291 Electrical Specifications............................................... 3 High Voltage Floating Current Source .................................... 14 ADR292 Electrical Specifications............................................... 4 Kelvin Connections .................................................................... 14 Absolute Maximum Ratings............................................................ 6 Low Power, Low Voltage Reference for Data Converters ..... 14 ESD Caution .................................................................................. 6 Voltage Regulator for Portable Equipment ............................. 15 Pin Configurations and Function Descriptions ........................... 7 Outline Dimensions ....................................................................... 16 Typical Performance Characteristics ............................................. 8 Ordering Guide .......................................................................... 17 Terminology .................................................................................... 12 REVISION HISTORY 5/11—Rev. E to Rev. F Deleted Negative Precision Reference Without Precision Resistors Section ............................................................................. 14 Deleted Figure 33 and Figure 34, Renumbered Sequentially ... 14 Changes to Ordering Guide .......................................................... 17 9/03—Rev. B to Rev. C Deleted ADR290 ................................................................. Universal Changes to Specifications .................................................................2 Changes to Ordering Guide .............................................................4 Updated Outline Dimensions ....................................................... 13 12/07—Rev. D to Rev. E Changes to Features.......................................................................... 1 Changes to Figure 34 ...................................................................... 14 3/06—Rev. C to Rev. D Updated Format .................................................................. Universal Change to Table 8 ............................................................................. 6 Updated Outline Dimensions ....................................................... 15 Changes to Ordering Guide .......................................................... 16 Rev. F | Page 2 of 20 ADR291/ADR292 SPECIFICATIONS ADR291 ELECTRICAL SPECIFICATIONS VS = 3.0 V to 15 V, TA = 25°C, unless otherwise noted. Table 2. Parameter E GRADE Output Voltage Initial Accuracy Symbol Conditions Min Typ Max Unit VOUT VOERR IOUT = 0 mA 2.498 –2 –0.08 2.500 2.502 +2 +0.08 V mV % F GRADE Output Voltage Initial Accuracy VOUT VOERR IOUT = 0 mA 2.497 –3 –0.12 2.500 2.503 +3 +0.12 V mV % G GRADE Output Voltage Initial Accuracy VOUT VOERR IOUT = 0 mA 2.494 –6 –0.24 2.500 2.506 +6 +0.24 V mV % ∆VOUT/∆VIN IOUT = 0 mA 30 40 100 125 ppm/V ppm/V ∆VOUT/∆ILOAD VS = 5.0 V, IOUT = 0 mA to 5 mA 100 125 ∆VOUT eN eN After 1000 hours of operation @ 125°C 0.1 Hz to 10 Hz @ 1 kHz 30 40 50 8 480 ppm/mA ppm/mA ppm μV p-p nV/√Hz Typ Max Unit LINE REGULATION E/F Grades G Grade LOAD REGULATION E/F Grades G Grade LONG-TERM STABILITY NOISE VOLTAGE WIDEBAND NOISE DENSITY VS = 3.0 V to 15 V, TA = −25°C to +85°C, unless otherwise noted. Table 3. Parameter TEMPERATURE COEFFICIENT E Grade F Grade G Grade LINE REGULATION E/F Grades G Grade LOAD REGULATION E/F Grades G Grade Symbol Conditions TCVOUT IOUT = 0 mA 3 5 10 8 15 25 ppm/°C ppm/°C ppm/°C ∆VOUT/∆VIN IOUT = 0 mA 35 50 125 150 ppm/V ppm/V ∆VOUT/∆ILOAD VS = 5.0 V, IOUT = 0 mA to 5 mA 20 30 125 150 ppm/mA ppm/mA Rev. F | Page 3 of 20 Min ADR291/ADR292 VS = 3.0 V to 15 V, TA = −40°C to+125°C, unless otherwise noted. Table 4. 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 Symbol Conditions TCVOUT THERMAL HYSTERESIS VOUT-HYS Min Typ Max Unit IOUT = 0 mA 3 5 10 10 20 30 ppm/°C ppm/°C ppm/°C ∆VOUT/∆VIN IOUT = 0 mA 40 70 200 250 ppm/V ppm/V ∆VOUT/∆ILOAD VS = 5.0 V, IOUT = 0 mA to 5 mA IS TA = 25°C −40°C ≤ TA ≤ +125°C 8-lead SOIC, 8-lead TSSOP 20 30 9 12 50 200 300 12 15 ppm/mA ppm/mA μA μA ppm ADR292 ELECTRICAL SPECIFICATIONS VS = 5 V to 15 V, TA = 25°C, unless otherwise noted. Table 5. Parameter E GRADE Output Voltage Initial Accuracy Symbol Conditions Min Typ Max Unit VOUT VOERR IOUT = 0 mA 4.093 −3 −0.07 4.096 4.099 +3 +0.07 V mV % F GRADE Output Voltage Initial Accuracy VOUT VOERR IOUT = 0 mA 4.092 −4 −0.10 4.096 4.1 +4 +0.10 V mV % G GRADE Output Voltage Initial Accuracy VOUT VOERR IOUT = 0 mA 4.090 −6 −0.15 4.096 4.102 +6 +0.15 V mV % ∆VOUT/∆VIN VS = 4.5 V to 15 V, IOUT = 0 mA 30 40 100 125 ppm/V ppm/V ∆VOUT/∆ILOAD VS = 5.0 V, IOUT = 0 mA to 5 mA 100 125 ∆VOUT After 1000 hours of operation @ 125°C 0.1 Hz to 10 Hz @ 1 kHz 30 40 50 ppm/mA ppm/mA ppm LINE REGULATION E/F Grades G Grade LOAD REGULATION E/F Grades G Grade LONG-TERM STABILITY NOISE VOLTAGE WIDEBAND NOISE DENSITY eN eN Rev. F | Page 4 of 20 12 640 μV p-p nV/√Hz ADR291/ADR292 VS = 5 V to 15 V, TA = −25°C to +85°C, unless otherwise noted. Table 6. Parameter TEMPERATURE COEFFICIENT E Grade F Grade G Grade LINE REGULATION E/F Grades G Grade LOAD REGULATION E/F Grades G Grade Symbol Conditions TCVOUT Min Typ Max Unit IOUT = 0 mA 3 5 10 8 15 25 ppm/°C ppm/°C ppm/°C ∆VOUT/ΔVIN VS = 4.5 V to 15 V, IOUT = 0 mA 35 50 125 150 ppm/V ppm/V ∆VOUT/∆ILOAD VS = 5.0 V, IOUT = 0 mA to 5 mA 20 30 125 150 ppm/mA ppm/mA Typ Max Unit VS = 5 V to 15 V, TA = −40°C to +125°C, unless otherwise noted. Table 7. 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 Symbol Conditions TCVOUT IOUT = 0 mA 3 5 10 10 20 30 ppm/°C ppm/°C ppm/°C ∆VOUT/∆VIN VS = 4.5 V to 15 V, IOUT = 0 mA 40 70 200 250 ppm/V ppm/V ∆VOUT/∆ILOAD VS = 5.0 V, IOUT = 0 mA to 5 mA IS 200 300 15 18 THERMAL HYSTERESIS VOUT-HYS TA = 25°C −40°C ≤ TA ≤ +125°C 8-lead SOIC, 8-lead TSSOP 20 30 10 12 50 ppm/mA ppm/mA μA μA ppm Rev. F | Page 5 of 20 Min ADR291/ADR292 ABSOLUTE MAXIMUM RATINGS Remove power before inserting or removing units from their sockets. Table 9. Package Types Package Type 8-Lead SOIC (R) 8-Lead TSSOP (RU) 3-Lead TO-92 (T) Table 8. Parameter Supply Voltage Output Short-Circuit Duration to GND Storage Temperature Range T, R, RU Packages Operating Temperature Range ADR291/ADR292 Junction Temperature Range T, R, RU Packages Lead Temperature (Soldering, 60 sec) Rating 18 V Indefinite 1 −65°C to +150°C −40°C to +125°C −65°C to +125°C 300°C Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. θJA1 158 240 160 θJC 43 43 – Unit °C/W °C/W °C/W θJA is specified for worst-case conditions. For example, θJA is specified for a device in socket testing. In practice, θJA is specified for a device soldered in the circuit board. Table 10. Other XFET Products Part Number ADR420 ADR421 ADR423 ADR425 ESD CAUTION Rev. F | Page 6 of 20 Nominal Output Voltage (V) 2.048 2.50 3.0 5.0 Package Type 8-Lead MSOP/SOIC 8-Lead MSOP/SOIC 8-Lead MSOP/SOIC 8-Lead MSOP/SOIC ADR291/ADR292 PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS NC 7 NC 6 VOUT TOP VIEW GND 4 (Not to Scale) 5 NC NC = NO CONNECT GND Figure 4. 8-Lead SOIC (R-8) NC 1 VIN 2 NC 3 GND 4 ADR291/ ADR292 TOP VIEW (Not to Scale) 8 NC 7 NC 6 VOUT 5 NC NC = NO CONNECT VOUT 3 2 Pin No. TSSOP 1, 3, 5, 7, 8 2 4 6 Figure 5. 8-Lead TSSOP (RU-8) TO-92 N/A 1 2 3 Mnemonic NC VIN GND VOUT Rev. F | Page 7 of 20 VIN ADR291 TOP VIEW (Not to Scale) Figure 6. 3-Lead TO-92 (T-3) Table 11. Pin Function Descriptions SOIC 1, 3, 5, 7, 8 2 4 6 1 00163-038 NC 3 8 00163-037 VIN 2 ADR291/ ADR292 00163-036 NC 1 Description No Connect Input Voltage Ground Output Voltage ADR291/ADR292 TYPICAL PERFORMANCE CHARACTERISTICS 2.506 14 3 TYPICAL PARTS VS = 5V 12 QUIESCENT CURRENT (μA) 2.500 2.498 2.496 0 –25 25 50 75 100 TA = –40°C 6 4 2 00163-004 2.494 –50 TA = +25°C 8 0 125 00163-007 2.502 TA = +125°C 10 0 2 4 6 8 10 INPUT VOLTAGE (V) TEMPERATURE (°C) Figure 7. ADR291 VOUT vs. Temperature 3 TYPICAL PARTS VS = 5V 4.100 12 SUPPLY CURRENT (µA) 4.098 4.096 4.094 ADR291 ADR292 10 8 6 00163-005 4.092 4.090 –50 –25 0 25 50 75 100 4 –50 125 00163-008 OUTPUT VOLTAGE (V) 16 14 VS = 5V –25 0 25 50 75 100 125 TEMPERATURE (°C) TEMPERATURE (°C) Figure 8. ADR292 VOUT vs. Temperature Figure 11. ADR291/ADR292 Supply Current vs. Temperature 100 14 ADR291: VS = 3.0V TO 15V ADR292: VS = 4.5V TO 15V 12 LINE REGULATION (ppm/V) TA = +25°C 8 TA = –40°C 6 4 2 0 2 4 6 8 10 INPUT VOLTAGE (V) 12 IOUT = 0 mA 80 TA = +125°C 10 00163-006 QUIESCENT CURRENT (μA) 14 Figure 10. ADR292 Quiescent Current vs. Input Voltage 4.102 0 12 14 60 ADR292 40 20 00163-009 OUTPUT VOLTAGE (V) 2.504 ADR291 0 –50 16 –25 0 25 50 75 100 125 TEMPERATURE (°C) Figure 12. ADR291/ADR292 Line Regulation vs. Temperature Figure 9. ADR291 Quiescent Current vs. Input Voltage Rev. F | Page 8 of 20 ADR291/ADR292 200 100 VS = 5V IOUT = 0 mA LOAD REGULATION (ppm/mA) 60 ADR291 40 20 ADR292 0 –50 00163-010 LINE REGULATION (ppm/V) 80 –25 0 25 50 75 100 160 IOUT = 1mA 120 IOUT = 5mA 80 40 0 –50 125 00163-013 ADR291: VS = 3.0V TO 15V ADR292: VS = 4.5V TO 15V –25 0 Figure 13. ADR291/ADR292 Line Regulation vs. Temperature 125 0.5 TA = +25°C 0.4 0.3 TA = –40°C 0.2 00163-011 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 LOAD CURRENT (mA) 4.0 4.5 160 120 IOUT = 1mA IOUT = 5mA 80 40 0 –50 5.0 00163-014 LOAD REGULATION (ppm/mA) –25 0 25 50 75 100 125 TEMPERATURE (°C) Figure 14. ADR291 Minimum Input-Output Voltage Differential vs. Load Current Figure 17. ADR292 Load Regulation vs. Temperature 0 0.7 –250 0.6 ∆VOUT FROM NOMINAL (µV) TA = +125°C 0.5 TA = +25°C 0.4 0.3 0.2 TA = –40°C 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 LOAD CURRENT (mA) 4.0 4.5 –750 TA = –40°C –1000 TA = +125°C –1250 –1500 –1750 00163-012 0.1 TA = +25°C –500 –2000 0.1 5.0 Figure 15. ADR292 Minimum Input-Output Voltage Differential vs. Load Current 00163-015 DIFFERENTIAL VOLTAGE (V) 100 VS = 5V TA = +125°C 0.1 DIFFERENTIAL VOLTAGE (V) 75 200 0.6 0 50 Figure 16. ADR291 Load Regulation vs. Temperature 0.7 0 25 TEMPERATURE (°C) TEMPERATURE (°C) 1 SOURCING LOAD CURRENT (mA) Figure 18. ADR291 ΔVOUT from Nominal vs. Load Current Rev. F | Page 9 of 20 10 ADR291/ADR292 0 1s 100 –1000 –1550 90 TA = +25°C TA = –40°C TA = +125°C 2μV p-p –2000 –2500 10 –3000 0% –4000 0.1 00163-016 –3500 00163-019 ∆VOUT FROM NOMINAL (µV) –500 1 SOURCING LOAD CURRENT (mA) 10 Figure 22. ADR291 0.1 Hz to 10 Hz Noise Figure 19. ADR292 ΔVOUT from Nominal vs. Load Current 1000 VS = 5V IL = 0 mA VIN = 15V TA = 25°C 800 OUTPUT IMPEDANCE (Ω) 40 700 ADR291 500 400 300 200 20 10 100 0 10 30 100 FREQUENCY (Hz) 0 1000 00163-020 600 00163-017 VOLTAGE NOISE DENSITY (nV/√Hz) 900 50 ADR292 0 120 1k 10k 50 VS = 5V IL = 0 mA VS = 5V 100 OUTPUT IMPEDANCE (Ω) 40 80 60 40 30 20 100 FREQUENCY (Hz) 0 1000 00163-021 10 20 00163-018 RIPPLE REJECTION (dB) 100 FREQUENCY (Hz) Figure 23. ADR291 Output Impedance vs. Frequency Figure 20. Voltage Noise Density vs. Frequency 0 10 10 0 10 100 FREQUENCY (Hz) 1k Figure 24. ADR292 Output Impedance vs. Frequency Figure 21. ADR291/ADR292 Ripple Rejection vs. Frequency Rev. F | Page 10 of 20 10k ADR291/ADR292 IL = 5mA 500μ s IL = 5mA 1ms 100 100 90 90 10 10 0% 0% 1V 00163-022 ON 1V Figure 25. ADR291 Load Transient IL = 5mA CL = 1nF OFF 00163-025 OFF Figure 28. ADR291 Turn-On Time IL = 0mA 1ms 100 100 90 90 10ms 10 0% 1V 00163-023 10 0% 1V Figure 26. ADR291 Load Transient 00163-026 ON Figure 29. ADR291 Turn-Off Time 18 IL = 5mA CL = 100nF 16 5ms 14 100 90 12 FREQUENCY ON 10 8 6 10 2 00163-024 1V 00163-027 4 0% 0 –200 –180 –160 –140 –120 –100 –80 –60 –40 –20 0 20 40 60 80 100 120 140 160 180 200 MORE OFF TEMPERATURE +25°C ≥ –40°C ≥ +85°C ≥ +25°C VOUT DEVIATION (ppm) Figure 30. Typical Hysteresis for the ADR291 Product Figure 27. ADR291 Load Transient Rev. F | Page 11 of 20 ADR291/ADR292 TERMINOLOGY Line Regulation Line regulation refers to the change in output voltage due to a specified change in input voltage. It includes the effects of selfheating. Line regulation is expressed as percent-per-volt, partsper-million-per-volt, or microvolts-per-volt change in input voltage. Load Regulation The change in output voltage is due to a specified change in load current and includes the effects of self-heating. Load regulation is expressed in microvolts-per-milliampere, partsper-million-per-milliampere, or ohms of dc output resistance. Long-Term Stability Long-term stability refers to the typical shift of output voltage at 25°C on a sample of parts subjected to a test of 1000 hours at 125°C. TCVO [ppm/ ° C ] = VOUT (t 0 ) − VOUT (t 1 ) VOUT (t 0 ) VO (25° C ) × (T2 − T1 ) × 10 6 where: VOUT (25°C) = VOUT at 25°C. VOUT (T1) = VOUT at Temperature 1. VOUT (T2) = VOUT at Temperature 2. NC = no connect. There are internal connections at NC pins that are reserved for manufacturing purposes. Users should not connect anything at the NC pins. Thermal Hysteresis Thermal hysteresis is defined as the change of output voltage after the device is cycled through temperatures from +25°C to −40°C, then to +85°C, and back to +25°C. This is a typical value from a sample of parts put through such a cycle. ΔVOUT = VOUT (t 0 ) − VOUT (t 1 ) ΔVOUT [ppm ] = VO (T2 ) − VO (T1 ) VOUT −HYS = VOUT (25° C) − VOUT_TC × 10 6 VΟUT −HYS [ppm] = where: VOUT (t0) = VOUT at 25°C at Time 0. VOUT (t1) = VOUT at 25°C after 1000 hours of operation at 125°C. Temperature Coefficient Temperature coefficient is the change of output voltage over the operating temperature change, normalized by the output voltage at 25°C, expressed in ppm/°C. The equation follows: VOUT (25°C ) − VOUT_TC VOUT (25° C) × 10 6 where: VOUT (25°C) = VOUT at 25°C. VOUT_TC = VOUT at 25°C after temperature cycle from +25°C to −40°C, then to +85°C, and back to +25°C. Rev. F | Page 12 of 20 ADR291/ADR292 THEORY OF OPERATION The core of the XFET reference consists of two junction field effect transistors, one having 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 band gap references. Because most of the noise of a band gap reference comes from the compensation circuitry, the intrinsic temperature coefficient offers a significant advantage (being about 30 times lower), and therefore, requiring less correction resulting in much lower noise. The simplified schematic in Figure 31 shows the basic topology of the ADR291/ADR292 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 ⎛ R1 + R 2 + R3 ⎞ VOUT = ΔVP ⎜ ⎟ + (I PTAT ) (R3) R1 ⎝ ⎠ DEVICE POWER DISSIPATION CONSIDERATIONS The ADR291/ADR292 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 the output voltage chosen). 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. Use the following formula to calculate maximum junction temperature or dissipation of a device: PD = BASIC VOLTAGE REFERENCE CONNECTIONS References, in general, require a bypass capacitor connected from the VOUT pin to the GND pin. The circuit in Figure 32 illustrates the basic configuration for the ADR291/ADR292 family of references. Note that the decoupling capacitors are not required for circuit stability. NC 1 2 + The various versions of the ADR291/ADR292 family are created by on-chip adjustment of R1 and R3 to achieve 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 dropout voltage. VIN I1 1 VP R1 R2 VOUT IPTAT R3 CHANNEL IMPLANT R1 + R2 + R3 × ΔVP = IPTAT × R3 VOUT = R1 00163-028 GND 1 EXTRA θ JA where TJ and TA are the junction and ambient temperatures, respectively. PD is the device power dissipation. θJA is the device package thermal resistance. where: ΔVP is the difference in pinch-off voltage between the two FETs. IPTAT is the positive temperature coefficient correction current. I1 TJ − TA NC 10µF ADR291/ ADR292 8 NC 7 NC 3 6 4 5 VOUT 0.1µF 0.1µF NC NC = NO CONNECT 00163-029 The ADR291/ADR292 series of references uses a 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. Figure 32. Basic Voltage Reference Configuration NOISE PERFORMANCE The noise generated by the ADR291/ADR292 family of references is typically less than 12 μV p-p over the 0.1 Hz to 10 Hz band. The noise measurement is made with a band-pass 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 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 it takes for the active circuits to settle and for the thermal gradients on the chip to stabilize. Figure 28 shows the turn-on settling time for the ADR291. Figure 31. ADR291/ADR292 Simplified Schematic Rev. F | Page 13 of 20 ADR291/ADR292 APPLICATIONS INFORMATION HIGH VOLTAGE FLOATING CURRENT SOURCE The circuit shown in Figure 33 can be used to generate a floating current source with minimal self-heating. This particular configuration operates on high supply voltages determined by the breakdown voltage of the N-channel JFET. +VS E231 SILICONIX 2 VIN One such ADC for which the ADR291 is well suited is the AD7701. Figure 35 shows the ADR291 used as the reference for this converter. The AD7701 is a 16-bit ADC 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 (Σ-Δ) ADC, calibration microcontroller with on-chip static RAM, a clock oscillator, and a serial communications port. 2N3904 OP90 GND 4 00163-032 2.10kΩ –VS The ADR291/ADR292 family has a number of features that makes it ideally suited for use with analog-to-digital and digitalto-analog converters. Because of its low supply voltage, the ADR291 can be used with converters that run on 3 V supplies without having to add a higher supply voltage for the reference. The low quiescent current (12 μA maximum) and low noise, tight temperature coefficient, combined with the high accuracy of the ADR291/ADR292, make it ideal for low power applications such as handheld, battery-operated equipment. Figure 33. High Voltage Floating Current Source KELVIN CONNECTIONS In many portable instrumentation applications, the PC board area is directly related to cost; therefore, circuit interconnects are reduced to a minimal width. These narrow lines can cause large voltage drops if the voltage reference is required to provide load currents to various functions. In fact, circuit interconnects can exhibit a typical line resistance of 0.45 mΩ/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 shown in Figure 34 overcomes the problem by including the wiring resistance within the forcing loop of the op amp. Since the op amp senses the load voltage, the op amp loop control forces the output to compensate for the wiring error producing the correct voltage at the load. 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 μW), the entire circuit still consumes about 25 mW. +5V ANALOG SUPPLY AVDD 0.1µF 2 ADR291/ ADR292 A1 VOUT 6 BP/UP ANALOG INPUT AIN ANALOG GROUND AGND 0.1µF DATA READY READ (TRANSMIT) SCLK SERIAL CLOCK SDATA SERIAL CLOCK 0.1µF CLKIN CLKOUT SC1 SC2 DGND AVSS +VOUT FORCE CS CAL CALIBRATE –5V ANALOG SUPPLY 0.1µF MODE DRDY RANGES SELECT 100kΩ 0.1µF DVSS 10µF Figure 35. Low Power, Low Voltage Supply Reference for the AD7701 A1 = 1/2 OP295 00163-033 4 ADR291 SLEEP RL 1µF GND RLW DVDD VREF AD7701 +VOUT SENSE VIN VIN VOUT GND VIN RLW 10µF 0.1µF Figure 34. Advantage of Kelvin Connection Rev. F | Page 14 of 20 00163-034 ADR291/ ADR292 LOW POWER, LOW VOLTAGE REFERENCE FOR DATA CONVERTERS ADR291/ADR292 CHARGER INPUT The ADR291/ADR292 family of references is ideal for providing a stable, low cost, and low power reference voltage in portable equipment power supplies. Figure 36 shows how the ADR291 and 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. 0.1µF R3 510kΩ 2 VIN ADR291/ ADR292 6V LEAD-ACID + BATTERY Rev. F | Page 15 of 20 VOUT 6 NC 3 GND 2 7 OP20 3 4 6 IRF9530 4 5V, 100mA R1 402kΩ 1% R2 402kΩ 1% C1 68µF TANT + + C2 1000µF ELECT Figure 36. Voltage Regulator for Portable Equipment 00163-035 VOLTAGE REGULATOR FOR PORTABLE EQUIPMENT ADR291/ADR292 OUTLINE DIMENSIONS 5.00 (0.1968) 4.80 (0.1890) 8 1 5 4 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) COPLANARITY 0.10 SEATING PLANE 6.20 (0.2441) 5.80 (0.2284) 1.75 (0.0688) 1.35 (0.0532) 0.51 (0.0201) 0.31 (0.0122) 8 0.50 (0.0196) 0.25 (0.0099) 45° 1 8° 0° 0.25 (0.0098) 0.17 (0.0067) 4 0.65 BSC 0.15 0.05 1.20 MAX COPLANARITY 0.10 0.30 0.19 SEATING 0.20 PLANE 0.09 0.75 0.60 0.45 Figure 38. 8-Lead Thin Shrink Small Outline Package [TSSOP] (RU-8) Dimensions shown in millimeters 0.050 (1.27) MAX 0.019 (0.482) SQ 0.016 (0.407) 0.165 (4.19) 0.125 (3.18) 0.055 (1.40) 0.045 (1.15) 3 2 0.135 (3.43) MIN 8° 0° COMPLIANT TO JEDEC STANDARDS MO-153-AA Figure 37. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) 0.205 (5.21) 0.175 (4.45) 6.40 BSC PIN 1 1.27 (0.0500) 0.40 (0.0157) COMPLIANT TO JEDEC STANDARDS MS-012-A A CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. 0.210 (5.33) 0.170 (4.32) 5 4.50 4.40 4.30 012407-A 4.00 (0.1574) 3.80 (0.1497) 3.10 3.00 2.90 0.105 (2.66) 0.095 (2.42) 1 0.115 (2.92) 0.080 (2.03) 0.500 (12.70) MIN 0.115 (2.92) 0.080 (2.03) SEATING PLANE BOTTOM VIEW COMPLIANT TO JEDEC STANDARDS TO-226-AA CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. Figure 39. 3-Lead Plastic Header-Style Package [TO-92] (T-3) Dimensions shown in inches and (millimeters) Rev. F | Page 16 of 20 ADR291/ADR292 ORDERING GUIDE Model 1 ADR291ERZ ADR291ERZ-REEL7 ADR291FRZ ADR291FRZ-REEL ADR291FRZ-REEL7 ADR291GRZ ADR291GRZ-REEL ADR291GRZ-REEL7 ADR291GRUZ ADR291GRUZ-REEL ADR291GRUZ-REEL7 ADR291GT9Z ADR292ERZ ADR292ERZ-REEL ADR292FRZ ADR292FRZ-REEL ADR292FRZ-REEL7 ADR292GRZ ADR292GRZ-REEL7 ADR292GRUZ ADR292GRUZ-REEL7 1 Output Voltage 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 4.096 4.096 4.096 4.096 4.096 4.096 4.096 4.096 4.096 Initial Accuracy (±%) 0.08 0.08 0.12 0.12 0.12 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.07 0.07 0.10 0.10 0.10 0.15 0.15 0.24 0.15 Temperature Coefficient Max (ppm/°C) 8 8 15 15 15 25 25 25 25 25 25 25 8 8 15 15 15 25 25 25 25 Z = RoHS Compliant Part. Rev. F | Page 17 of 20 Package Description 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead TSSOP 8-Lead TSSOP 8-Lead TSSOP 3-Lead TO-92 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead TSSOP 8-Lead TSSOP Package Option R-8 R-8 R-8 R-8 R-8 R-8 R-8 R-8 RU-8 RU-8 RU-8 T-3 R-8 R-8 R-8 R-8 R-8 R-8 R-8 RU-8 RU-8 Ordering Quantity 98 1,000 98 2,500 1,000 98 2,500 1,000 98 1,000 1,000 98 98 2,500 98 2,500 1,000 98 1,000 98 1,000 ADR291/ADR292 NOTES Rev. F | Page 18 of 20 ADR291/ADR292 NOTES Rev. F | Page 19 of 20 ADR291/ADR292 NOTES ©2007–2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D00163-0-5/11(F) Rev. F | Page 20 of 20