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FEATURES Wide Operating Range: 50 A-10 mA Initial Accuracy: 0.1% max Temperature Drift: 50 ppm/ C max Output Impedance: 0.5 max Wideband Noise (10 Hz-10 kHz): 20 V 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
1.2 V Micropower, Precision Shunt Voltage Reference AD1580
PIN CONFIGURATION SOT-23 Package
V+ 1 3 NC (OR V-) V- 2 TOP VIEW
NC = NO CONNECT
50 45
GENERAL DESCRIPTION
QUANTITY
40 35 30 25 20 15 10 5 0 -40 -30 -20 -10 10 20 0 TEMPERATURE DRIFT - ppm/C 30 40
The AD1580 is a low cost, two-terminal (shunt), precision bandgap reference. It provides an accurate 1.225 V output for input currents between 50 A and 10 mA. The AD1580's superior accuracy and stability is made possible by the precise matching and thermal tracking of on-chip components. Proprietary curvature correction design techniques have been used to minimize the nonlinearities in the voltage output temperature characteristics. The AD1580 is stable with any value of capacitive load. The low minimum operating current makes the AD1580 ideal for use in battery powered 3 V or 5 V systems. However, the wide operating current range means that the AD1580 is extremely versatile and suitable for use in a wide variety of high current applications. The AD1580 is available in two grades, A and B, both of which are provided in an SOT-23 package, the smallest surface mount package available on the market. Both grades are specified over the industrial temperature range of -40C to +85C.
Reverse Voltage Temperature Drift Distribution
300
250
200
1. Portable, Battery-Powered Equipment: Cellular Phones, Notebook Computers, PDAs, GPS and DMM. 2. Computer Workstations Suitable for use with a wide range of video RAMDACs. 3. Smart Industrial Transmitters 4. PCMCIA Cards. 5. Automotive. 6. 3 V/5 V 8-12-Bit Data Converters.
QUANTITY
TARGET APPLICATIONS
150
100
50
0 -10
-8
-6
-4
-2
0
2
4
6
8
10
OUTPUT ERROR - mV
Reverse Voltage Error Distribution
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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. (c) Analog Devices, Inc., 1995 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
AD1580-SPECIFICATIONS (@ T = +25 C, I
A
IN
= 100 A, unless otherwise noted)
Min 1.224 AD1580B Typ Max 1.225 1.226 50 50 2.5 0.5 0.4 20 5 5 80 +85 +125 -40 -55 +85 +125 5 Units V ppm/C A mV mV V rms V p-p s V C C
Model Min Reverse Voltage Output Reverse Voltage Temperature Drift -40C to +85C Minimum Operating Current, TMIN to TMAX Reverse Voltage Change with Reverse Current 50 A < IIN < 10 mA, TMIN to TMAX 50 A < IIN < 1 mA, TMIN to TMAX Dynamic Output Impedance (VR/IR) IIN = 1 mA 100 A (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
AD1580A Typ Max 1.225 1.235 100 50 2.5 0.5 0.4 20 5 5 80 5
1.215
1
0.5
Temperature Range Specified Performance, TMIN to TMAX Operating Range3
-40 -55
NOTES 1 Measured with no load capacitor. 2 Output hysteresis is defined as the change in the +25C output voltage after a temperature excursion to +85C and then to -40C. 3 The operating temperature range is defined as the temperature extremes at which the device will continue to function. Parts may deviate from their specified performance. Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS 1
ORDERING GUIDE
Model AD1580ART AD1580ART-REEL1 AD1580ART-REEL72 AD1580BRT AD1580BRT-REEL1 AD1580BRT-REEL72 Initial Output Error 10 mV 10 mV 10 mV 1 mV 1 mV 1 mV Temperature Coefficient 100 ppm/C 100 ppm/C 100 ppm/C 50 ppm/C 50 ppm/C 50 ppm/C Package Option RT RT RT RT RT RT
Reverse Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 mA Forward Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 mA Internal Power Dissipation2 SOT-23 (RT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 Watts Storage Temperature Range . . . . . . . . . . . . -65C to +150C Operating Temperature Range AD1580/RT . . . . . . . . . . . . . . . . . . . . . . . - 55C to +125C Lead Temperature, Soldering Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . +215C Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . +220C ESD Susceptibility3 Human Body Model . . . . . . . . . . . . . . . . . . . . . . . . . . 4 kV Machine Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 V
NOTES 1 Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and 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. 2 Specification is for device in free air at +25C: SOT-23 Package: JA = 300C/Watt. 3 The human body model is a 100 pF capacitor discharged through 1.5 k. For the machine model, a 200 pF capacitor is discharged directly into the device.
NOTES 1 Provided on a 13-inch reel containing 7,000 pieces. 2 Provided on a 7-inch reel containing 2,000 pieces.
PACKAGE BRANDING INFORMATION
Four marking fields identify the device generic, grade, and date of processing. The first field is the product identifier. A "0" identifies the generic as the AD1580. The second field indicates the device grade; "A" or "B." In the third field a numeral or letter indicates a calendar year; "5" for 1995, "A" for 2001. In the fourth field, letters A-Z represent a two week window within the calendar year; starting with "A" for the first two weeks of January.
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 AD1580 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
-2-
REV. 0
Typical Performance Characteristics-AD1580
1000
600
REVERSE VOLTAGE CHANGE - ppm
500
NOISE VOLTAGE - nV/Hz
0
400
-500
~20ppm/C
-1000
200
-1500
-2000 -55
-35
-15
5 25 65 45 TEMPERATURE - C
85
105
125
1.0
10
100 1k 10k FREQUENCY - Hz
100k
1M
Figure 1. Output Drift for Different Temperature Characteristics
Figure 3. Noise Spectral Density
4
100
REVERSE VOLTAGE CHANGE - mV
3
80 REVERSE CURRENT - A
2
TA = 125C
60
1 TA = -40C - +85C
40
+85C
0
20
+25C -40C
-1 0.01
0.1 1 REVERSE CURRENT - mA
10
0
0
0.2
0.4 0.6 0.8 1.0 REVERSE VOLTAGE - V
1.2
1.4
Figure 2. Output Voltage Error vs. Reverse Current
Figure 4. Reverse Current vs. Reverse Voltage
1.0 +25C
-40C 0.8
FORWARD VOLTAGE - V
+85C 0.6
0.4
0.2
0 0.01
0.1
1 10 FORWARD CURRENT - mA
100
Figure 5. Forward Voltage vs. Forward Current
REV. 0
-3-
AD1580
THEORY OF OPERATION
VS RS VR IR VOUT I R + IL IL VR VOUT +5V(+3V) 10% 2.94k (1.30k)
The AD1580 uses the "bandgap" 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 approximately a -2 mV/C temperature coefficient, 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 will go to approximately the silicon bandgap voltage. Thus, if a voltage could be developed with an opposing temperature coefficient to sum with VBE, a zero TC reference would result. The AD1580 circuit in Figure 6, provides such a compensating voltage, V1 by driving two transistors at different current densities and amplifying the resultant VBE difference (VBE-- which has a positive TC). The sum of VBE and V1 provide a stable voltage reference.
V+
RS
(a)
(b)
Figure 7. Typical Connection Diagram
TEMPERATURE PERFORMANCE
The AD1580 is designed for reference applications where stable temperature performance is important. Extensive temperature testing and characterization ensures that the device's performance is maintained over the specified temperature range. 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 centigrade, i.e., 50 ppm/C. However, because of nonlinearities in temperature characteristics which 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 different temperatures to guarantee that the voltage will fall within the given error band. The proprietary curvature correction design techniques used to minimize the AD1580 nonlinearities allow the temperature performance to be guaranteed using the maximum deviation method. This method is of more use to a designer than the one which simply guarantees the maximum error band over the entire temperature change. Figure 8 shows a typical output voltage drift for the AD1580 and illustrates the methodology. The maximum slope of the two diagonals drawn from the initial output value at 25C to the output values at 85C and -40C determines the performance grade of the device. For a given grade of the AD1580 the designer can easily determine the maximum total error from the initial tolerance plus temperature variation. For example, the AD1580BRT initial tolerance is 1 mV, a 50 ppm/C temperature coefficient corresponds to an error band of 4 mV
1.2258 1.2256 1.2254
OUTPUT VOLTAGE - V
V1
VBE
VBE
V-
Figure 6. Schematic Diagram
APPLYING THE AD1580
The AD1580 is simple to use in virtually all applications. To operate the AD1580 as a conventional shunt regulator (Figure 7a), an external series resistor is connected between the supply voltage and the AD1580. For a given supply voltage the series resistor, RS, determines the reverse current flowing through the AD1580. The value of RS must be chosen to accommodate the expected variations of the supply voltage, VS, load current, IL, and the AD1580 reverse voltage, VR, while maintaining an acceptable reverse current, IR, through the AD1580. 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. The equation for selecting RS is as follows: RS = (VS - VR )/(IR + IL ) Figure 7b shows a typical connection with the AD1580BRT operating at a minimum of 100 A that can provide 1 mA to its load, while accommodating 10% power supply variations.
(VMAX - VO) SLOPE = TC = -------------------------- (85C - 25C) x 1.225 x 10-6 VMAX
1.2252 1.2250 1.2248 1.2246 1.2244 1.2242 1.2240 1.2238 -55 VMIN -35 -15 45 5 25 65 TEMPERATURE - C 85 105 125 (VMIN - VO) SLOPE = TC = --------------------------- (-40C - 25C) x 1.225 x 10-6 VO
Figure 8. Output Voltage vs. Temperature
-4-
REV. 0
AD1580
(50 x 10-6 x 1.225 V x 65C) thus, the unit is guaranteed to be 1.225 V 5 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 AD1580 will produce a curve similar to that in Figures 1 and 8.
VOLTAGE OUTPUT NONLINEARITY VERSUS TEMPERATURE OUTPUT IMPEDANCE VERSUS FREQUENCY
OUTPUT IMPEDANCE -
When using a reference 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. This characteristic (Figure 9) is generated by normalizing the measured drift characteristic to the end point average drift. The residual drift error of approximately 500 ppm shows that the AD1580 is compatible with systems that require 10-bit accurate temperature performance.
600
Understanding the effect of the reverse dynamic output impedance in a practical application may be important to successfully apply the AD1580. A voltage divider is formed by the AD1580's output impedance and the external source impedance. When using an external source resistor of about 30 k (IR = 100 A), 1% of the noise from a 100 kHz switching power supply is developed at the output of the AD1580. Figure 11 shows how a 1 F load capacitor connected directly across the AD1580 reduces the affect of power supply noise to less than 0.01%.
1k
100 CL = 0
10 IR = 0.1IR IR = 100A 1 IR = 1mA
RESIDUAL DRIFT ERROR - ppm
500
CL = 1F
400
300
0.1 10
100
1k 10k FREQUENCY - Hz
100k
1M
200
Figure 11. Output Impedance vs. Frequency
NOISE PERFORMANCE AND REDUCTION
-35 -15 5 65 25 45 TEMPERATURE - C 85 105 125
100
0 -55
Figure 9. Residual Drift Error
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 +25C after operation at +85C, and the output, also at +25C after operation at -40C. Figure 10 displays the hysteresis associated with AD1580. This characteristic exists in all references and has been minimized in the AD1580.
40 35 30 25 20 15 10 5 0 -400
The noise generated by the AD1580 is typically less than 5 V p-p over the 0.1 Hz to 10 Hz band. Figure 12 shows the 0.1 Hz to 10 Hz noise of a typical AD1580. Noise in a 10 Hz-10 kHz bandwidth is approximately 20 V rms (Figure 13a). If further noise reduction is desired, a 1-pole low-pass filter may be added between the output pin and ground. A time constant of 0.2 ms will have a -3 dB point at about 800 Hz, and will reduce the high frequency noise to about 6.5 V rms, (Figure 13b). A time constant of 960 ms will have a -3 dB point at 165 Hz, and will reduce the high frequency noise to about 2.9 V rms (Figure 13c).
4.5V p-p
QUANTITY
1V/DIV
1s/DIV
Figure 12. 0.1 Hz-10 Hz Voltage Noise
-300 -200 -100 0 100 200 300 400 HYSTERESIS VOLTAGE - V
Figure 10. Reverse Voltage Hysteresis Distribution
REV. 0
-5-
AD1580
40V/DIV
21V rms
Output turn-on time is modified when an external noise reduction filter is used. When present, the time constant of the filter will dominate overall settling.
(a)
2.4V
20V/DIV
6.5V rms = 0.2ms (b)
VIN 0V
10V/DIV
2.9V rms = 960ms (c)
OUTPUT ERROR 1mV/DIV 2 s/DIV
10ms/DIV
Figure 13. Total RMS Noise
TURN-ON TIME
OUTPUT 0.5mV/DIV 2 ms/DIV
Many low power instrument manufacturers are becoming increasingly concerned with the turn-on characteristics of components being used in their systems. Fast turn-on components often enable the end user to keep power off when not needed, and yet respond quickly when the power is turned on for operation. Figure 14a displays the turn-on characteristic of the AD1580. 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 15 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 us, and there is no long thermal tail when the horizontal scale is expanded to 2 ms/div.
2.4V VIN
Figure 15. Turn-On Settling
TRANSIENT RESPONSE
Many A/D and D/A converters present transient current loads to the reference, and poor reference response can degrade the converter's performance. Figure 16 displays both the coarse and fine settling characteristics of the device to load transients of 50 A.
20mV/DIV 1mV/DIV
IR = 100A + 50A STEP
(a)
(b)
IR = 100A - 50A STEP
0V
CL = 200pF
20mV/DIV
1mV/DIV
1s/DIV
Figure 16. Transient Settling
250mV/DIV
5s/DIV
Figure 16a shows the settling characteristics of the device for an increased reverse current of 50 A. Figure 16b shows the response when the reverse current is decreased by 50 A. The transients settle to 1 mV in about 3 s. Attempts to drive a large capacitive load (in excess of 1,000 pF) may result in ringing, as shown in the step response photo (Figure 17). 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 14b. A resistor isolates the capacitive load from the output stage, while the capacitor provides a single pole lowpass filter and lowers the output noise.
Figure 14a. Response Time
RS = 11.5k RL
VIN
VR
CL
VOUT
Figure 14b. Turn-On, Settling, and Transient Test Circuit
-6-
REV. 0
AD1580
2.0V VIN
1.8V
One family of ADCs that the AD1580 is well suited for is the AD7714-3 and AD7715-3. The AD7714/AD7715 are chargebalancing (sigma-delta) A/D converters 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 19 shows the AD1580 connected to the AD7714/AD7715 for 3 V operation.
3V
CL = 0.01F
34.8k REFIN(+) RSW 5k (TYP) CREF (3-8pF) SWITCHING FREQUENCY DEPENDS ON FCLKIN
AD7714/15-3
HIGH IMPEDANCE >1G
10mV/DIV
50s/DIV
AD1580
REFIN(-)
Figure 17. Transient Response with Capacitive Load
PRECISION MICROPOWER LOW DROPOUT REFERENCE
Figure 19. Reference Circuit for the AD7714/AD7715-3
The circuit in Figure 18 provides an ideal solution for making 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 AD1580 output voltage, VR. Output voltages as high as 2.1 V can supply 1 mA of load current. A one-pole filter connected between the AD1580 and the OP193 input may be used to achieve low output noise. The nominal quiescent power consumption is a mere 200 W.
3V 34.8k 205 4.7F
The AD1580 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 (Figure 20), the impedance seen looking into the IOUT2 terminal changes with DAC code. If the AD1580 drives IOUT2 and AGND directly, less than 0.2 LSBs of additional linearity error will result. The buffer amp eliminates any linearity degradation that could result from variations in the reference level .
+3.3V
OP193
VOUT = +1.225V OR VOUT = +1.225 (1+R2/R3)
VDD VREF
RBF IOUT1
C1
VIN
DAC
IOUT2 AGND
A1
VOUT
AD1580
AD7943/45/48
R3 R2
DGND +3.3V
A1: OP295 AD822 OP2283
41.2k
Figure 18. Micropower Buffered Reference
AD1580
A1
USING THE AD1580 WITH 3 V DATA CONVERTERS
SIGNAL GROUND
The AD1580's low output drift (50 ppm/C) and compact subminiature SOT-23 package makes it ideally suited for today's high performance converters in space critical applications.
Figure 20. Single Supply System
REV. 0
-7-
AD1580
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
SOT-23
0.1200 (3.048) 0.1102 (2.799)
0.550 (1.397) 0.0470 (1.194) PIN 1 0.0236 (0.599) 0.0177 (0.450) 0.0807 (2.050) 0.0701 (1.781)
0.1040 (2.642) 0.0827 (2.101)
0.0413 (1.049) 0.0374 (0.950) 0.0059 (0.150) 0.0440 (1.118) 0.0034 (0.086) 0.0320 (0.813) 0.0210 (0.533) 0.0146 (0.371) 0.0100 (0.254) 0.0050 (0.127) 0.027 (0.686) REF
0.0040 (0.102) 0.0005 (0.013) SEATING PLANE
TAPE AND REEL DIMENSIONS
Dimensions shown in millimeters.
1.8 0.1 0.30 0.05 14.4 MAX
+0.05 1.5 -0.00
4.0 0.10 2.0 0.05
1.75 0.10 180 (7") OR 330 (13")
1.5 MIN
13.0 0.2 50 (7") MIN OR 100 (13") MIN
3.5 0.05
2.7 0.1
8.0 0.30
20.2 MIN
3.1 0.1 DIRECTION OF UNREELING 1.0 MIN 0.75 MIN 8.4 +1.5 -0.0
-8-
REV. 0
PRINTED IN U.S.A.
C2081-18-10/95

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