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1.2 V Micropower, Precision Shunt Voltage Reference
PIN CONFIGURATION
SOT-23 PackageReverse Voltage Temperature Drift Distribution
Reverse Voltage Error Distribution
REV.0
1.2 V Micropower, Precision
Shunt Voltage Reference
FEATURES
Wide Operating Range:50mA–10
mA
Initial Accuracy:60.1% max
Temperature Drift:650 ppm/8C max
Output Impedance:0.5V max
Wideband Noise (10 Hz–10 kHz):20 mV rms
Operating Temperature Range:–408C to +858C
High ESD Rating
4 kV Human Body Model
400 V Machine Model
Compact, Surface-Mount, SOT-23 Package
GENERAL DESCRIPTIONThe AD1580 is a low cost, two-terminal (shunt), precision
bandgap 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 an SOT-23 package, the smallest surface mount
package available on the market. 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, GPS and
DMM.Computer Workstations
Suitable for use with a wide range of video RAMDACs.Smart Industrial TransmittersPCMCIA Cards.Automotive.3 V/5 V 8–12-Bit Data Converters.
AD1580–SPECIFICATIONSNOTESMeasured 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.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.
(@ TA = +258C, IIN = 100 mA, unless otherwise noted)
CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V readily
ABSOLUTE MAXIMUM RATINGS1Reverse Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 mA
Forward Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 mA
InternalPowerDissipation2
SOT-23(RT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3Watts
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
NOTESStresses 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.Specification is for device in free air at +25°C: SOT-23 Package: θJA = 300°C/Watt.The 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 GUIDENOTES
1Provided on a 13-inch reel containing 7,000 pieces.
2Provided on a 7-inch reel containing 2,000 pieces.
PACKAGE BRANDING INFORMATIONFour 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.
REVERSE VOLTAGE CHANGE – ppm
TEMPERATURE – °C
–1500Figure 1. Output Drift for Different Temperature
Characteristics
REVERSE VOLTAGE CHANGE – mV
REVERSE CURRENT – mAFigure 2.Output Voltage Error vs. Reverse Current
Figure 3.Noise Spectral Density
Figure 4.Reverse Current vs. Reverse Voltage
FORWARD CURRENT – mA
FORWARD VOLTAGE – V
0.6Figure 5.Forward Voltage vs. Forward Current
AD1580
THEORY OF OPERATIONThe 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 –2mV/°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 (ΔVBE—
which has a positive TC). The sum of VBE and V1 provide a
stable voltage reference.
VBEFigure 6.Schematic Diagram
APPLYING THE AD1580The 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 μA that can provide ±1 mA to
(a)(b)
Figure 7.Typical Connection Diagram
TEMPERATURE PERFORMANCEThe 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 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. For example, the
AD1580BRT initial tolerance is ±1mV, a ±50ppm/°C
temperature coefficient corresponds to an error band of ±4mV
OUTPUT VOLTAGE – V
1.2242
(50 × 10–6 × 1.225 V × 65°C) thus, the unit is guaranteed to be
1.225V ± 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
TEMPERATUREWhen 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 normal-
izing 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 9.Residual Drift Error
REVERSE VOLTAGE HYSTERESISA major requirement for high performance industrial equipment
manufacturers is a consistent output voltage at nominal tempera-
ture 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, also at +25°C after operation at –40°C. Figure 10
displays the hysteresis associated with AD1580. This characteristic
exists in all references and has been minimized in the AD1580.
QUANTITY
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 using an external source resistor of aboutkΩ (IR = 100 μA), 1% of the noise from a 100kHz switching
power supply is developed at the output of the AD1580. Figure
11 shows how a 1μF load capacitor connected directly across
the AD1580 reduces the affect of power supply noise to less
than 0.01%.
OUTPUT IMPEDANCE –
100100k10k1k10
FREQUENCY – HzFigure 11.Output Impedance vs. Frequency
NOISE PERFORMANCE AND REDUCTIONThe noise generated by the AD1580 is typically less than 5 μV 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 μ 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 μV 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 μV rms (Figure
13c).
Figure 12.0.1Hz–10 Hz Voltage Noise
AD1580(a)
Figure 13.Total RMS Noise
TURN-ON TIMEMany 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 2ms/div.
Figure 14a.
VINVR
RS = 11.5kΩVOUTOutput 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.
Figure 15. Turn-On Settling
TRANSIENT RESPONSEMany 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±50μA.
Figure 16.Transient Settling
Figure 16a shows the settling characteristics of the device for an
increased reverse current of 50 μA. Figure 16b shows the
response when the reverse current is decreased by 50 μA. The
transients settle to 1 mV in about 3 μs.
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 low-
pass filter and lowers the output noise.
