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AD1580ART-REEL
1.2 V Micropower, Precision Shunt Voltage Reference
REV.B
1.2 V Micropower, Precision
Shunt Voltage Reference*. Patent No. 5,969,657; other patents pending.
FEATURES
Wide Operating Range:50�A to 10
mA
Initial Accuracy:�0.1% Max
Temperature Drift:�50 ppm/�C Max
Output Impedance:0.5� Max
Wideband Noise (10 Hz to 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 and SC70 Packages
PIN CONFIGURATIONS
SOT-23 PackageSC70 PackageFigure 1. Reverse Voltage Temperature Drift Distribution
Figure 2. Reverse Voltage Error Distribution
GENERAL DESCRIPTIONThe AD1580 is a low cost, 2-terminal (shunt), precision band
gap reference. It provides an accurate 1.225 V output for input
currents between 50 µA 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 the SOT-23 and SC70 packages, the smallest
surface-mount package available. Both grades are specified over
the industrial temperature range of –40°C to +85°C.
TARGET APPLICATIONSPortable, Battery-Powered Equipment:
Cellular Phones, Notebook Computers, PDAs, GPSes, and
DMMsComputer Workstations:
Suitable for use with a wide range of video RAMDACsSmart Industrial TransmittersPCMCIA CardsAutomotive3 V/5 V, 8-Bit to 12-Bit Data Converters
AD1580–SPECIFICATIONSNOTES
1Measured with no load capacitor.Output hysteresis is defined as the change in the +25°C output voltage after a temperature excursion to +85°C and then to –40°C.
3The 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.
(@ TA = 25�C, IIN = 100 �A, unless otherwise noted.)
ABSOLUTE MAXIMUM RATINGS1Reverse Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 mA
Forward Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 mA
InternalPowerDissipation2
SOT-23(RT). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3W
Storage Temperature Range. . . . . . . . . . . . –65°C to +150°C
Operating Temperature Range
AD1580/RT. . . . . . . . . . . . . . . . . . . . . . . –55°C to +125°C
Lead Temperature, Soldering
Vapor Phase (60 sec). . . . . . . . . . . . . . . . . . . . . . . . +215°C
Infrared (15 sec). . . . . . . . . . . . . . . . . . . . . . . . . . . +220°C
ESD Susceptibility3
Human Body Model. . . . . . . . . . . . . . . . . . . . . . . . . . 4 kV
Machine Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 V
NOTES
1Stresses 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.
2Specification is for device in free air at 25°C: SOT-23 package: θJA = 300°C/W.
3The human body model is a 100pF capacitor discharged through 1.5kΩ. For the
machine model, a 200pF capacitor is discharged directly into the device.
ORDERING GUIDENOTESR2 is 250 piece reel.Provided on a 13-inch reel containing 10,000 pieces.Provided on a 7-inch reel containing 3,000 pieces.Z = Pb-free part.
PACKAGE BRANDING INFORMATIONIn the SOT-23 package (RT), 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 through Z represent a two-
week window within the calendar year, starting with A for the
first two weeks of January.
CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V readily
TPC 1. Output Drift for Different Temperature
Characteristics
TPC 2.Output Voltage Error vs. Reverse Current
TPC 3.Noise Spectral Density
TPC 4.Reverse Current vs. Reverse Voltage
TPC 5.Forward Voltage vs. Forward Current
AD1580
THEORY OF OPERATIONThe AD1580 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 –2mV/°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
will go to approximately the silicon band gap 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 Figure3 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 provides a stable voltage
reference.
VBEFigure 3.Schematic Diagram
APPLYING THE AD1580The AD1580 is simple to use in virtually all applications. To operate
the AD1580 as a conventional shunt regulator (Figure4a), 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 4b shows a typical connection of the AD1580BRT
operating at a minimum of 100 µA. This connection can provide
(a)(b)
Figure 4.Typical Connection Diagram
TEMPERATURE PERFORMANCEThe AD1580 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.
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, e.g., 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 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 that simply guarantees the maximum
error band over the entire temperature change.
Figure 5 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 +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 AD1580, the designer
can easily determine the maximum total error from the initial
tolerance plus temperature variation.
OUTPUT VOLTAGE (V)
TEMPERATURE (�C)
1.2242Figure 5.Output Voltage vs. Temperature
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 TPC 1 and
Figure5.
VOLTAGE OUTPUT NONLINEARITY VERSUS
TEMPERATUREWhen 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. This characteristic (Figure 6) is generated by normalizing
the measured drift characteristic to the end point average drift.
The residual drift error of approximately 500ppm shows that
the AD1580 is compatible with systems that require 10-bit
accurate temperature performance.
TEMPERATURE (�C)
RESIDUAL DRIFT ERROR (ppm)
100Figure 6.Residual Drift Error
REVERSE VOLTAGE HYSTERESISA 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 operation at +85°C and the
output, at +25°C after operation at –40°C. Figure 7 displays the
hysteresis associated with the AD1580. This characteristic exists in
all references and has been minimized in the AD1580.
QUANTITY
HYSTERESIS VOLTAGE (�V)–400
–300–200–1000100200400300Figure 7.Reverse Voltage Hysteresis Distribution
OUTPUT IMPEDANCE VERSUS FREQUENCYUnderstanding 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 an external
source resistor of about 30kΩ (IR = 100 µA) is used, 1% of the
noise from a 100kHz switching power supply is developed at
the output of the AD1580. Figure8 shows how a 1µF load
capacitor connected directly across the AD1580 reduces the
effect of power supply noise to less than 0.01%.
OUTPUT IMPEDANCE (
0.1100100k10k1k10
FREQUENCY (Hz) Figure 8.Output Impedance vs. Frequency
NOISE PERFORMANCE AND REDUCTIONThe noise generated by the AD1580 is typically less than 5µVp-p
over the 0.1 Hz to 10 Hz band. Figure 9 shows the 0.1 Hz toHz noise of a typical AD1580. Noise in a 10 Hz to 10kHz
bandwidth is approximately 20 µV rms (Figure 10a). 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 µV rms, (Figure 10b). 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 µV rms (Figure10c).
Figure 9.0.1Hz to 10 Hz Voltage Noise
