Low Noise, Micropower 5.0 V Precision Voltage Reference ADR293

Transcription

1 Low Noise, Micropower 5. V Precision Voltage Reference ADR93 FEATURES. V to 5 V supply range Supply current: 5 μa maximum Low noise: 5 μv p-p typical (. Hz to Hz) High output current: 5 ma Temperature range: C to +5 C Pin-compatible with the REF/REF9x APPLICATIONS Portable instrumentation Precision reference for 5 V systems ADC and DAC reference Solar-powered applications Loop-current powered instruments GENERAL DESCRIPTION The ADR93 is a low noise, micropower precision voltage reference that utilizes an XFET (extra implanted junction FET) reference circuit. The 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 longterm stability. The ADR93 is a series voltage reference providing stable and accurate output voltage from a. V supply. Quiescent current is only 5 μa maximum, making this device ideal for battery powered instrumentation. Three electrical grades are available offering initial output accuracy of ±3 mv, ± mv, and ± mv. Temperature coefficients for the three grades are 8 ppm/ C, PIN CONFIGURATIONS NC V IN NC 3 GND ADR93 TOP VIEW (Not to Scale) 8 NC 7 NC V 5 NC NC = NO CONNECT Figure. 8-Lead Narrow Body SOIC (R-8) NC 8 V IN ADR93 7 NC GND 3 TOP VIEW (Not to Scale) 5 NC NC V NC NC = NO CONNECT Figure. 8-Lead TSSOP (RU-8) 5 ppm/ C, and 5 ppm/ C maximum. Line regulation and load regulation are typically 3 ppm/v and 3 ppm/ma, respectively, maintaining the reference s overall high performance. The ADR93 is specified over the extended industrial temperature range of C to +5 C. This device is available in the 8-lead SOIC and 8-lead TSSOP packages. Table. ADR9x Products Device Output Voltage (V) Initial Accuracy (%) - - Temperature Coefficient (ppm/ C max) ADR9.5.8,.,. 8, 5, 5 ADR9.9.7,.,.5 8, 5, 5 ADR93 5..,.,. 8, 5, 5 Rev. 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. 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 9, Norwood, MA -9, U.S.A. Tel: Fax: Analog Devices, Inc. All rights reserved.

2 TABLE OF CONTENTS Features... Applications... Pin Configurations... General Description... Revision History... Specifications... 3 Electrical Specificiations... 3 Absolute Maximum Ratings... 5 Thermal Resistance... 5 ESD Caution... 5 Typical Performance Characteristics... Terminology... 9 Theory of Operation... Device Power Dissipation Considerations... Basic Voltage Reference Connections... Noise Performance... Turn-On Time... Applications... A Negative Precision Reference Without Precision Resistors... A Precision Current Source... Kelvin Connections... Voltage Regulator for Portable Equipment... Outline Dimensions... 3 Ordering Guide... REVISION HISTORY /7 Rev. A to Rev. B Updated Format...Universal Changes to Table... Updated Outline Dimensions... 3 Changes to Ordering Guide / Rev. to Rev. A Rev. B Page of

3 SPECIFICATIONS ELECTRICAL SPECIFICIATIONS VS =. V, TA = 5 C, unless otherwise noted. Table. Parameter Symbol Conditions Min Typ Max Unit PUT VOLTAGE V I = ma E Grade V F Grade V G Grade V INITIAL ACCURACY I = ma E Grade 3 +3 mv. % F Grade + mv. % G Grade + mv. % LINE REGULATION ΔV /ΔVIN. V to 5 V, I = ma E, F Grades 3 ppm/v G Grade 5 ppm/v LOAD REGULATION ΔV /ΔILOAD VS =. V, ma to 5 ma E, F Grades 3 ppm/ma G Grade 5 ppm/ma LONG-TERM STABILITY ΔV After hours of 5 C 5 ppm NOISE VOLTAGE en. Hz to Hz 5 μv p-p WIDEBAND NOISE DENSITY en at khz nv/ Hz VS =. V, TA = 5 C to +85 C, unless otherwise noted. Table 3. Parameter Symbol Conditions Min Typ Max Unit TEMPERATURE COEFFICIENT TCV I = ma E Grade 3 8 ppm/ C F Grade 5 5 ppm/ C G Grade 5 ppm/ C LINE REGULATION ΔV/ΔVIN. V to 5 V, I = ma E, F Grades 35 5 ppm/v G Grade 5 ppm/v LOAD REGULATION ΔV/ΔILOAD VS =. V, ma to 5 ma E, F Grades 5 ppm/ma G Grade 3 ppm/ma Rev. B Page 3 of

4 VS =. V, TA = C to +5 C, unless otherwise noted. Table. Parameter Symbol Conditions Min Typ Max Unit TEMPERATURE COEFFICIENT TCV I = ma E Grade 3 ppm/ C F Grade 5 ppm/ C G Grade 3 ppm/ C LINE REGULATION ΔV/ΔVIN. V to 5 V, I = ma E, F Grades ppm/v G Grade 7 5 ppm/v LOAD REGULATION ΔV/ΔILOAD VS =. V, ma to 5 ma E, F Grades ppm/ma G Grade 3 3 ppm/ma SUPPLY CURRENT 5 C 5 μa 5 μa THERMAL HYSTERESIS V-HYS 8-lead SOIC_N 7 ppm 8-lead TSSOP 57 ppm Rev. B Page of

5 ABSOLUTE MAXIMUM RATINGS Table 5. Parameter Rating Supply Voltage 8 V Output Short-Circuit Duration to GND Indefinite Storage Temperature Range 5 C to +5 C Operating Temperature Range C to +5 C Junction Temperature Range 5 C to +5 C Lead Temperature (Soldering, sec) 3 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. THERMAL RESISTANCE θja is specified for worst-case conditions; that is, θja is specified for device in socket testing. In practice, θja is specified for a device soldered in circuit board. Table. Thermal Resistance Package Type θja θjc Unit 8-Lead SOIC_N (R-8) 58 3 C/W 8-Lead TSSOP (RU-8) 3 C/W ESD CAUTION Rev. B Page 5 of

6 TYPICAL PERFORMANCE CHARACTERISTICS PUT VOLTAGE (V) 5. V S = V 3 TYPICAL PARTS LINE REGULATION (ppm/v) 8 V S = V TO 5V TEMPERATURE ( C) Figure 3. V vs. Temperature TEMPERATURE ( C) Figure. Line Regulation vs. Temperature - T A = +5 C V S = V TO 9V I = ma SUPPLY CURRENT (µa) 8 T A = +5 C T A = C LINE REGULATION (ppm/v) 8 8 INPUT VOLTAGE (V) Figure. Supply Current vs. Input Voltage TEMPERATURE ( C) Figure 7. Line Regulation vs. Temperature -7.7 SUPPLY CURRENT (µa) 8 V S = V DIFFERENTIAL VOLTAGE (V) T A = +5 C T A = +5 C T A = C TEMPERATURE ( C) Figure 5. Supply Current vs. Temperature LOAD CURRENT (ma) Figure 8. Minimum Input/Output Voltage Differential vs. Load Current -8 Rev. B Page of

7 LOAD REGULATION (ppm/ma) 8 V S = V I = 5mA I = ma TEMPERATURE ( C) Figure 9. Load Regulation vs. Temperature -9 RIPPLE REJECTION (db) 8 V S = V k FREQUENCY (Hz) Figure. Ripple Rejection vs. Frequency - ΔV FROM NOMINAL (mv) 3 T A = +5 C T A = C T A = +5 C PUT IMPEDANCE (Ω) 5 3 V S = V I L = ma k SOURCING LOAD CURRENT (ma) Figure. ΔV from Nominal vs. Load Current - k k FREQUENCY (Hz) Figure 3. Output Impedance vs. Frequency -3 VOLTAGE NOISE DENSITY (nv/ Hz) 8 V IN = 5V T A = 5 C µv p-p k FREQUENCY (Hz) Figure. Voltage Noise Density - Figure.. Hz to Hz Noise s/div - Rev. B Page 7 of

8 I L = 5mA I I = 5mA C L = nf 5V/DIV V/DIV Figure 5. Turn-On Time 5µs/DIV -5 Figure 8. Load Transient ms/div -8 I L = 5mA I I = 5mA C L = nf 5V/DIV V/DIV Figure. Turn-Off Time 5µs/DIV - Figure 9. Load Transient ms/div -9 I L = 5mA FREQUENCY IN NUMBER OF UNITS 8 8 TEMPERATURE +5 C C +85 C +5 C Figure 7. Load Transient ms/div V DEVIATION (ppm) Figure. Typical Hysteresis for ADR9x Product - Rev. B Page 8 of

9 TERMINOLOGY 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 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 microvolts per milliampere, parts per million per milliampere, or ohms of dc output resistance. Long-Term Stability Typical shift of output voltage of 5 C on a sample of parts subjected to high temperature operating life test of hours at 5 C. Δ V = V t V t ΔV [ ] ( ) ( ) V ( t ) V ( t ) V ( t ) ppm = where: V (t) = V at 5 C at time. V (t) = V at 5 C after hours operation at 5 C. NC = No Connect There are in fact connections at NC pins, which are reserved for manufacturing purposes. Users should not connect anything at NC pins. Temperature Coefficient The change of output voltage over the operating temperature change and normalized by the output voltage at 5 C, expressed in ppm/ C. TC V [ C] ( Τ ) V ( T ) ( 5 C) ( T ) T V ppm/ = V where: V (5 C) = V at 5 C. V (T) = V at Temperature. V (T) = V at Temperature. Thermal Hysteresis Thermal hysteresis is defined as the change of output voltage after the device is cycled through temperatures from +5 C to C to +85 C and back to +5 C. This is a typical value from a sample of parts put through such a cycle. V HYS = V ( 5 C) V TC V ( 5 C) V TC V HYS [ ppm ] = V ( 5 C) where: V (5 C) = V at 5 C. V-TC = V (5 C) after temperature cycle at +5 C to C to +85 C and back to +5 C. Rev. B Page 9 of

10 THEORY OF OPERATION The ADR93 uses a new reference generation technique known as XFET, which yields a reference with low noise, low supply current, and very low thermal hysteresis. The core of the XFET reference consists of two junction field effect transistors, one of which has an extra channel implant to raise its pinch-off voltage. By running the two JFETs at the same drain current, the difference in pinch-off voltage can be amplified and used to form a highly stable voltage reference. The intrinsic reference voltage is around.5 V with a negative temperature coefficient of about 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. The big advantage over a band gap reference is that the intrinsic temperature coefficient is some 3 times lower (therefore, less correction is needed) and this results in much lower noise, because most of the noise of a band gap reference comes from the temperature compensation circuitry. The simplified schematic in Figure shows the basic topology of the ADR93. The temperature correction term is provided by a current source with value designed to be proportional to absolute temperature. The general equation is V where: R + R + R3 = ΔVP R + ( I )( R3) PTAT ΔVP is the difference in pinch-off voltage between the two FETs. IPTAT is the positive temperature coefficient correction current. 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. I I ΔV P V IN R R R3 EXTRA CHANNEL IMPLANT R + R + R3 V = ΔV P + I PTAT R3 R Figure. Simplified Schematic I PTAT GND V - DEVICE POWER DISSIPATION CONSIDERATIONS The ADR93 is guaranteed to deliver load currents to 5 ma with an input voltage that ranges from 5.5 V to 5 V. When this device is used in applications with large input voltages, care should be exercised to avoid exceeding the published specifications for maximum power dissipation or junction temperature that could result in premature device failure. The following formula should be used to calculate a device s maximum junction temperature or dissipation: TJ TA PD = θ JA where: TJ and TA are the junction temperature and ambient temperature, respectively. PD is the device power dissipation. θja is the device package thermal resistance. BASIC VOLTAGE REFERENCE CONNECTIONS References, in general, require a bypass capacitor connected from the V pin to the GND pin. The circuit in Figure illustrates the basic configuration for the ADR93. Note that the decoupling capacitors are not required for circuit stability. + µf NC NC 3.µF ADR93 NC = NO CONNECT 8 NC 7 NC V 5 NC Figure. Basic Voltage Reference Configuration NOISE PERFORMANCE.µF The noise generated by the ADR93 is typically less than 5 μv p-p over the. Hz to Hz band. The noise measurement is made with a band-pass filter made of a -pole high-pass filter with a corner frequency at. Hz and a -pole low-pass filter with a corner frequency at 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 for the active circuits to settle and the time for the thermal gradients on the chip to stabilize. Figure 5 shows the typical turn-on time for the ADR93. - Rev. B Page of

11 APPLICATIONS A NEGATIVE PRECISION REFERENCE WITH PRECISION RESISTORS In many current-output CMOS DAC applications where the output signal voltage must be of the same polarity as the reference voltage, it is often required to reconfigure a currentswitching DAC into a voltage-switching DAC by using a.5 V reference, an op amp, and a pair of resistors. Using a currentswitching DAC directly requires the need for an additional operational amplifier at the output to reinvert the signal. Therefore, a negative voltage reference is desirable from the point that an additional operational amplifier is not required for either reinversion (current-switching mode) or amplification (voltage-switching mode) of the DAC output voltage. In general, any positive voltage reference can be converted into a negative voltage reference by using an operational amplifier and a pair of matched resistors in an inverting configuration. The disadvantage to that approach is that the largest single source of error in the circuit is the relative matching of the resistors used. The circuit illustrated in Figure 3 avoids the need for tightly matched resistors with the use of an active integrator circuit. In this circuit, the output of the voltage reference provides the input drive for the integrator. To maintain circuit equilibrium, the integrator adjusts its output to establish the proper relationship between the reference s V and GND. One caveat with this approach should be mentioned. Although rail-to-rail output amplifiers work best in the application, these operational amplifiers require a finite amount (mv) of headroom when required to provide any load current. The choice for the circuit s negative supply should take this issue into account. V IN ADR93 GND V kω kω µf µf +5V A 5V Ω V REF A = / OP9, / OP95 Figure 3. A Negative Precision Voltage Reference Uses No Precision Resistors A PRECISION CURRENT SOURCE Many times in low power applications, the need arises for a precision current source that can operate on low supply voltages. As shown in Figure, the ADR93 is configured as a precision current source. The circuit configuration illustrated is a floating current source with a grounded load. The output -3 voltage of the reference is bootstrapped across RSET, which sets the output current into the load. With this configuration, circuit precision is maintained for load currents in the range from the reference s supply current, typically 5 μa to approximately 5 ma. V IN ADR93 GND V µf I SY ADJUST R L R P I Figure. A Precision Current Source R SET KELVIN CONNECTIONS In many portable instrumentation applications where PC board cost and area go hand-in-hand, circuit interconnects are very often of dimensionally minimum width. These narrow lines can cause large voltage drops if the voltage reference is required to provide load currents to various functions. In fact, a circuit s interconnects can exhibit a typical line resistance of.5 mω/ square ( 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 in Figure 5 overcomes the problem by including the wiring resistance within the forcing loop of the op amp. Because the op amp senses the load voltage, op amp loop control forces the output to compensate for the wiring error and to produce the correct voltage at the load. V IN ADR93 GND V µf kω V IN A R LW R LW Figure 5. Advantage of Kelvin Connection - +V SENSE +V FORCE R L -5 Rev. B Page of

12 VOLTAGE REGULATOR FOR PORTABLE EQUIPMENT The ADR93 is ideal for providing a stable, low cost, and low power reference voltage in portable equipment power supplies. Figure shows how the ADR93 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, V or higher, and an aluminum electrolytic capacitor, V or higher, are recommended for C and C, respectively. In addition, the path from the ground side of C and C to the ground side of R should be kept as short as possible. CHARGER INPUT V LEAD-ACID BATTERY.µF + V IN ADR93 V GND R kω % 7 3 OP R kω % R3 5kΩ C 8µF TANT IRF953 Figure. Voltage Regulator for Portable Equipment + 5V, ma + C µf ELECT - Rev. B Page of

13 LINE DIMENSIONS 5. (.98).8 (.89). (.57) 3.8 (.97) 8 5. (.) 5.8 (.8).5 (.98). (.) COPLANARITY. SEATING PLANE.7 (.5) BSC.75 (.88).35 (.53).5 (.).3 (.) 8.5 (.98).7 (.7).5 (.9).5 (.99).7 (.5). (.57) 5 COMPLIANT TO JEDEC STANDARDS MS--AA 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. Figure 7. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) 7-A BSC.5.5 PIN COPLANARITY..5 BSC.3.9. MAX SEATING PLANE COMPLIANT TO JEDEC STANDARDS MO-53-AA Figure 8. 8-Lead Thin Shrink Small Outline Package [TSSOP] (RU-8) Dimensions shown in millimeters Rev. B Page 3 of

14 ORDERING GUIDE Model Output Voltage (V) Initial Accuracy (%) Temperature Coefficient (ppm/ C max) Temperature Range Package Description Package Option Ordering Quantity ADR93ER C to +5 C 8-Lead SOIC_N R-8 98 ADR93ER-REEL C to +5 C 8-Lead SOIC_N R-8,5 ADR93ERZ C to +5 C 8-Lead SOIC_N R-8 98 ADR93ERZ-REEL C to +5 C 8-Lead SOIC_N R-8,5 ADR93FR C to +5 C 8-Lead SOIC_N R-8 98 ADR93FRZ C to +5 C 8-Lead SOIC_N R-8 98 ADR93GR C to +5 C 8-Lead SOIC_N R-8 98 ADR93GR-REEL C to +5 C 8-Lead SOIC_N R-8, ADR93GRZ C to +5 C 8-Lead SOIC_N R-8 98 ADR93GRZ-REEL C to +5 C 8-Lead SOIC_N R-8, ADR93GRU C to +5 C 8-Lead TSSOP RU-8 9 ADR93GRU-REEL C to +5 C 8-Lead TSSOP RU-8,5 ADR93GRU-REEL C to +5 C 8-Lead TSSOP RU-8, ADR93GRUZ C to +5 C 8-Lead TSSOP RU-8 9 ADR93GRUZ-REEL C to +5 C 8-Lead TSSOP RU-8,5 ADR93GRUZ-REEL C to +5 C 8-Lead TSSOP RU-8, Z = RoHS Compliant Part. Rev. B Page of

15 NOTES Rev. B Page 5 of

16 NOTES 7 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C--/7(B) Rev. B Page of