Data Sheet
AD780
2.5 V/3.0 V High Precision Reference
FEATURES
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FUNCTIONAL BLOCK DIAGRAM
Pin programmable 2.5 V or 3.0 V output
Ultralow drift: 3 ppm/°C max
High accuracy: 2.5 V or 3.0 V ±1 mV max
Low noise: 100 nV/√Hz
Noise reduction capability
Low quiescent current: 1 mA max
Output trim capability
Plug-in upgrade for present references
Temperature output pin
Series or shunt mode operation (±2.5 V, ±3.0 V)
Figure 1.
GENERAL DESCRIPTION
The AD780 is an ultrahigh precision band gap reference voltage
that provides a 2.5 V or 3.0 V output from inputs between 4.0 V
and 36 V. Low initial error and temperature drift combined with
low output noise and the ability to drive any value of capacitance
make the AD780 the ideal choice for enhancing the performance
of high resolution analog-to-digital converters (ADCs) and digital-toanalog converters (DACs), and for any general-purpose precision
reference application. A unique low headroom design facilitates a
3.0 V output from a 5.0 V 10% input, providing a 20% boost to
the dynamic range of an ADC over performance with existing 2.5 V
references.
The AD780 can be used to source or sink up to 10 mA, and
can be used in series or shunt mode, thus allowing positive or
negative output voltages without external components. This makes
it suitable for virtually any high performance reference application.
Unlike some competing references, the AD780 has no region of
possible instability. The part is stable under all load conditions when
a 1 µF bypass capacitor is used on the supply.
PRODUCT HIGHLIGHTS
1. The AD780 provides a pin programmable 2.5 V or 3.0 V output
from a 4 V to 36 V input.
2. Laser trimming of both initial accuracy and temperature coefficients results in low errors over temperature without the use of
external components. The AD780BN has a maximum variation
of 0.9 mV from −40°C to +85°C.
3. For applications that require even higher accuracy, an optional
fine-trim connection is provided.
4. The AD780 noise is extremely low, typically 4 mV p-p from 0.1
Hz to 10 Hz and a wideband spectral noise density of typically
100 nV/√Hz. This can be further reduced, if desired, by using
two external capacitors.
5. The temperature output pin enables the AD780 to be configured
as a temperature transducer while providing a stable output
reference.
A temperature output pin on the AD780 provides an output voltage
that varies linearly with temperature, allowing the part to be configured as a temperature transducer while providing a stable 2.5 V or
3.0 V output.
The AD780 is a pin compatible performance upgrade for the
LT1019(A)–2.5 and the AD680. The latter is targeted toward low
power applications.
The AD780 is available in three grades in PDIP and SOIC
packages. The AD780AN, AD780AR, AD780BN, AD780BR, and
AD780CR are specified for operation from −40°C to +85°C.
Rev. J
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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.
Data Sheet
AD780
TABLE OF CONTENTS
Features................................................................ 1
Functional Block Diagram......................................1
General Description...............................................1
Product Highlights................................................. 1
Specifications........................................................ 3
Absolute Maximum Ratings...................................4
Thermal Resistance........................................... 4
Notes.................................................................. 4
ESD Caution.......................................................4
Theory of Operation...............................................5
Applying the AD780...............................................6
Noise Performance.............................................6
Noise Comparison..............................................7
Temperature Performance..................................7
Temperature Output Pin..................................... 7
Temperature Transducer Circuit.........................8
Supply Current Over Temperature..................... 8
Turn-On Time..................................................... 8
Dynamic Performance........................................8
Line Regulation.................................................. 9
Precision Reference for High Resolution 5 V
Data Converters............................................... 9
4.5 V Reference From 5 V Supply....................10
Negative (–2.5 V) Reference............................10
Outline Dimensions............................................. 12
Ordering Guide.................................................12
REVISION HISTORY
11/2022—Rev. I to Rev. J
Change to Load Regulation, Shunt Mode Parameter, Table 1 ........................................................................3
Changes to Ordering Guide........................................................................................................................... 12
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Rev. J | 2 of 12
Data Sheet
AD780
SPECIFICATIONS
TA = 25°C, VIN = 5 V, unless otherwise noted.
Table 1.
AD780AN/AD780AR
Parameter
OUTPUT VOLTAGE
2.5 V Out
3.0 V Out
SOLDER HEAT SHIFT
Mean
Sigma
OUTPUT VOLTAGE DRIFT1
−40°C to +85°C
−55°C to +125°C
LINE REGULATION
2.5 V Output, 4 V ≤ +VIN ≤ 36 V, TMIN to TMAX
3.0 V Output, 4.5 V ≤ +VIN ≤ 36 V, TMIN to TMAX
LOAD REGULATION, SERIES MODE
Sourcing 0 mA < IOUT < 10 mA
TMIN to TMAX
Sinking −10 mA < IOUT < 0 mA
−40°C to +85°C
−55°C to +125°C
LOAD REGULATION, SHUNT MODE
1 mA < ISHUNT < 10 mA
QUIESCENT CURRENT, 2.5 V SERIES MODE2
–40°C to +85°C
−55°C to +125°C
MINIMUM SHUNT CURRENT
OUTPUT NOISE
0.1 Hz to 10 Hz
Spectral Density, 100 Hz
LONG-TERM STABILITY3
TRIM RANGE
TEMPERATURE PIN
Voltage Output @ 25°C
Temperature Sensitivity
Output Resistance
SHORT-CIRCUIT CURRENT TO GROUND
TEMPERATURE RANGE
Specified Performance (A, B, C)
Operating Performance (A, B, C)4
1
Min
Typ
2.495
2.995
AD780CR
Max
Min
2.505
3.005
2.4985
2.9950
−1.1
0.4
0.75
0.8
0.7
Min
2.5015
3.0050
2.499
2.999
Max
Unit
2.501
3.001
V
V
−1.1
0.4
mV
mV
7
20
3
ppm/°C
ppm/°C
10
10
10
10
10
10
µV/V
µV/V
50
75
75
75
150
50
75
75
75
150
50
75
75
75
150
µV/mA
µV/mA
µV/mA
µV/mA
µV/mA
75
75
75
µV/mA
1.0
1.3
1.0
mA
mA
mA
1.0
1.3
1.0
0.75
0.8
0.7
1.0
1.3
1.0
0.75
0.8
0.7
4
100
20
4
100
20
4.0
560
1.9
3
30
Typ
7
20
4.0
−40
−55
AD780BN/AD780BR
Max
−1.1
0.4
4
100
20
500
Typ
620
500
+85
+125
−40
−55
µV p-p
nV/√Hz
± ppm/1000 Hr
±%
4.0
560
1.9
3
30
620
500
+85
+125
−40
−55
560
1.9
3
30
620
mV
mV/°C
kΩ
mA
+85
+125
°C
°C
Maximum output voltage drift is guaranteed for all packages.
2
3.0 V mode typically adds 100 µA to the quiescent current. Also, Iq increases by 2 µA/V above an input voltage of 5 V.
3
The long-term stability specification is noncumulative. The drift in subsequent 1,000 hour periods is significantly lower than in the first 1,000 hour period.
4
The operating temperature range is defined as the temperature extremes at which the device will still function. Parts may deviate from their specified performance outside
their specified temperature range.
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Rev. J | 3 of 12
Data Sheet
AD780
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter
Values
+VIN to Ground
TRIM Pin to Ground
TEMP Pin to Ground
Power Dissipation (25°C)
Storage Temperature
Lead Temperature (Soldering 10
sec)
Output Protection
36 V
36 V
36 V
500 mW
−65°C to +150°C
300°C
ESD Classification
Output safe for indefinite short to ground and
momentary short to VIN
Class 1 (1000 V)
Stresses at or above those listed under Absolute Maximum Ratings
may cause permanent damage to the product. This is a stress
rating only; functional operation of the product at these or any other
conditions above those indicated in the operational section of this
specification is not implied. Operation beyond the maximum operating conditions for extended periods may affect product reliability.
Figure 3. Die Layout
NOTES
Both VOUT pads must be connected to the output.
Die Thickness: The standard thickness of Analog Devices, Inc.
bipolar dice is 10 mil ± 1 mil.
Die Dimensions: The dimensions given are the maximum possible
die size.
Backing: The standard backside surface is silicon (not plated).
Analog Devices does not recommend gold-backed dice for most
applications.
Figure 2. Pin Configuration, 8-Lead PDIP and SOIC Packages
THERMAL RESISTANCE
Thermal performance is directly linked to PCB design and operating
environment. Careful attention to PCB thermal design is required.
Table 3. Thermal Resistance
Package Type1
θJA
θJC2
Unit
N-8
R-8
49.8
160
37.4
36.8
°C/W
°C/W
1
2
Values in Table 3 are calculated based on standard JEDEC test conditions
unless otherwise specified.
100 μm TIM is used for the θJC test. TIM is assumed to have 3.6 W/mK.
Table 4. Die Physical Characteristics
Parameter
Value
Units
Die Size
Back Grind Thickness
Bond Pad Opening Size
Top Metal Composition
Passivation
Polyimide
Die Marker
Substrate Bias
67 × 96
10
89 × 136
AlCu (0.5%)
Oxynitride
None
780
GND
mil
mil
µm
%
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µm
Edges: A diamond saw is used to separate wafers into dice,
thus providing perpendicular edges halfway through the die. In
contrast to scribed dice, this technique provides a more uniform
die shape and size. The perpendicular edges facilitate handling
(such as tweezer pickup), while the uniform shape and size simplify
substrate design and die attach.
Top Surface: The standard top surface of the die is covered by a
layer of passivation. All areas are covered except bonding pads and
scribe lines.
Surface Metallization: The metallization to Analog Devices bipolar
dice is aluminum/copper. The minimum thickness is 10,000 Å.
Bonding Pads: All bonding pads have a minimum size of 4.0 mil by
6.0 mil. The passivation windows have a minimum size of 3.5 mil by
5.3 mil.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although
this product features patented or proprietary protection circuitry,
damage may occur on devices subjected to high energy ESD.
Therefore, proper ESD precautions should be taken to avoid
performance degradation or loss of functionality.
V
Rev. J | 4 of 12
Data Sheet
AD780
THEORY OF OPERATION
Band gap references are the high performance solution for low
supply voltage and low power voltage reference applications. In
this technique, a voltage with a positive temperature coefficient
is combined with the negative coefficient of a transistor’s Vbe to
produce a constant band gap voltage.
In the AD780, the band gap cell contains two NPN transistors
(Q6 and Q7) that differ in emitter area by 12×. The difference in
their Vbes produces a PTAT current in R5. This, in turn, produces
a PTAT voltage across R4 that, when combined with the Vbe of
Q7, produces a voltage (Vbg) that does not vary with temperature.
Precision laser trimming of the resistors and other patented circuit
techniques are used to further enhance the drift performance.
The output voltage of the AD780 is determined by the configuration
of Resistors R13, R14, and R15 in the amplifier’s feedback loop.
This sets the output to either 2.5 V or 3.0 V, depending on whether
R15 (Pin 8) is grounded or not connected.
A unique feature of the AD780 is the low headroom design of the
high gain amplifier, which produces a precision 3 V output from an
input voltage as low as 4.5 V (or 2.5 V from a 4.0 V input). The
amplifier design also allows the part to work with +VIN = VOUT when
current is forced into the output terminal. This allows the AD780 to
work as a 2-terminal shunt regulator, providing a −2.5 V or −3.0 V
reference voltage output without external components.
The PTAT voltage is also used to provide the user with a thermometer output voltage (at Pin 3) that increases at a rate of approximately 2 mV/°C.
The DNC (Pin 7) of the AD780 is a 20 kΩ resistor to +VIN that is
used solely for production test purposes. Users who are currently
using the LT1019 self-heater pin (Pin 7) must take into account the
different load on the heater supply.
Figure 4. Schematic Diagram
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Rev. J | 5 of 12
Data Sheet
AD780
APPLYING THE AD780
The AD780 can be used without any external components to
achieve specified performance. If power is supplied to Pin 2 and Pin
4 is grounded, Pin 6 provides a 2.5 V or 3.0 V output depending on
whether Pin 8 is left unconnected or grounded.
A bypass capacitor of 1 µF (+VIN to GND) should be used if the
load capacitance in the application is expected to be greater than 1
nF. The AD780 in 2.5 V mode typically draws 700 µA of Iq at 5 V.
This increases by ~2 µA/V up to 36 V.
Figure 6. Compensation and Load Capacitor Combinations
C1 and C2 also improve the settling performance of the AD780
when subjected to load transients. The improvement in noise performance is shown in Figure 7, Figure 8, Figure 9, and Figure 10.
Figure 5. Optional Fine-Trim Circuit
Initial error can be nulled using a single 25 kΩ potentiometer
connected between VOUT, TRIM, and GND. This is a coarse trim
with an adjustment range of 4%, and is only included here for
compatibility purposes with other references. A fine trim can be
implemented by inserting a large value resistor (e.g., 1 MΩ to 5
MΩ) in series with the wiper of the potentiometer (see Figure 5).
The trim range, expressed as a fraction of the output, is simply
greater than or equal to 2.1 kΩ/RNULL for either the 2.5 V or 3.0 V
mode.
The external null resistor affects the overall temperature coefficient
by a factor equal to the percentage of VOUT nulled.
Figure 7. Standalone Noise Performance
For example, a 1 mV (0.03%) shift in the output caused by the trim
circuit, with a 100 ppm/°C null resistor, adds less than 0.06 ppm/°C
to the output drift (0.03% × 200 ppm/°C, since the resistors internal
to the AD780 also have temperature coefficients of less than 100
ppm/°C).
NOISE PERFORMANCE
The impressive noise performance of the AD780 can be further
improved, if desired, by adding two capacitors: a load capacitor
(C1) between the output and ground, and a compensation capacitor
(C2) between the TEMP pin and ground. Suitable values are shown
in Figure 6.
Figure 8. Standalone Noise Performance
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Rev. J | 6 of 12
Data Sheet
AD780
APPLYING THE AD780
Figure 9. Noise Reduction Circuit
Figure 11. Typical AD780BN Temperature Drift
NOISE COMPARISON
TEMPERATURE OUTPUT PIN
The wideband noise performance of the AD780 can also be expressed in ppm. The typical performance with C1 and C2 is 0.6
ppm; without external capacitors, typical performance is 1.2 ppm.
The AD780 provides a TEMP output (Pin 3) that varies linearly with
temperature. This output can be used to monitor changes in system
ambient temperature, and to initiate calibration of the system, if
desired. The voltage VTEMP is 560 mV at 25°C, and the temperature
coefficient is approximately 2 mV/°C.
This performance is, respectively, 7× and 3× lower than the specified performance of the LT1019.
Figure 12 shows the typical VTEMP characteristic curve over temperature taken at the output of the op amp with a noninverting gain of
5.
Figure 10. Reduced Noise Performance with C1 = 100 µF, C2 = 100 nF
TEMPERATURE PERFORMANCE
The AD780 provides superior performance over temperature by
means of a combination of patented circuit design techniques, precision thin-film resistors, and drift trimming. Temperature performance is specified in terms of ppm/°C; because of nonlinearity in the
temperature characteristic, the box test method is used to test and
specify the part. The nonlinearity takes the form of the characteristic
S-shaped curve shown in Figure 11. The box test method forms
a rectangular box around this curve, enclosing the maximum and
minimum output voltages over the specified temperature range. The
specified drift is equal to the slope of the diagonal of this box.
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Figure 12. Temperature Pin Transfer Characteristic
Since the TEMP voltage is acquired from the band gap core circuit,
current pulled from this pin has a significant effect on VOUT. Care
must be taken to buffer the TEMP output with a suitable op amp,
for example, an OP07, AD820, or AD711 (all of which would result
in less than a 100 µV change in VOUT). The relationship between
ITEMP and VOUT is
∆VOUT = 5.8 mV/µA ITEMP (2.5 V Range)
or
∆VOUT = 6.9 mV/µA ITEMP (3.0 V Range)
Rev. J | 7 of 12
Data Sheet
AD780
APPLYING THE AD780
Notice how sensitive the current dependent factor on VOUT is. A
large amount of current, even in tens of microamps, drawn from the
TEMP pin can cause the VOUT and TEMP output to fail.
The choice of C1 and C2 was dictated primarily by the need for
a relatively flat response that rolled off early in the high frequency
noise at the output. However, there is considerable margin in the
choice of these capacitors. For example, the user can actually put
a huge C2 on the TEMP pin with none on the output pin. However,
one must either put very little or a lot of capacitance at the TEMP
pin. Intermediate values of capacitance can sometimes cause oscillation. In any case, the user should follow the recommendation in
Figure 6.
TEMPERATURE TRANSDUCER CIRCUIT
The circuit shown in Figure 13 is a temperature transducer that
amplifies the TEMP output voltage by a gain of a little over +5 to
provide a wider full-scale output range. The digital potentiometer
can be used to adjust the output so it varies by exactly 10 mV/°C.
To minimize resistance changes with temperature, resistors with
low temperature coefficients, such as metal film resistors, should be
used.
Figure 14. Typical Supply Current over Temperature
TURN-ON TIME
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.
The two major factors that affect this are the active circuit settling
time and the time for the thermal gradients on the chip to stabilize.
Typical settling performance is shown in Figure 15. The AD780
settles to within 0.1% of its final value within 10 µs.
Figure 13. Differential Temperature Transducer
SUPPLY CURRENT OVER TEMPERATURE
The quiescent current of the AD780 varies slightly over temperature
and input supply range. The test limit is 1 mA over the industrial
and 1.3 mA over the military temperature range. Typical performance with input voltage and temperature variation is shown in
Figure 14.
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Figure 15. Turn-On Settling Time Performance
DYNAMIC PERFORMANCE
The output stage of the AD780 has been designed to provide
superior static and dynamic load regulation.
Figure 16 and Figure 17 show the performance of the AD780 while
driving a 0 mA to 10 mA load.
Rev. J | 8 of 12
Data Sheet
AD780
APPLYING THE AD780
Figure 19. Settling under Dynamic Capacitive Load
Figure 16. Transient Resistive Load Test Circuit
LINE REGULATION
Line regulation is a measure of change in output voltage due
to a specified change in input voltage. It is intended to simulate
worst-case unregulated supply conditions and is measured in µV/V.
Figure 20 shows typical performance with 4.0 V < VIN < 15.0 V.
Figure 17. Settling Under Transient Resistive Load
The dynamic load may be resistive and capacitive. For example,
the load may be connected via a long capacitive cable. Figure 18
and Figure 19 show the performance of the AD780 driving a 1000
pF, 0 mA to 10 mA load.
Figure 20. Output Voltage Change vs. Input Voltage
PRECISION REFERENCE FOR HIGH
RESOLUTION 5 V DATA CONVERTERS
The AD780 is ideally suited to be the reference for most 5 V
high resolution ADCs. The AD780 is stable under any capacitive
load, has superior dynamic load performance, and its 3.0 V output
provides the converter with the maximum dynamic range without
requiring an additional and expensive buffer amplifier. One of the
many ADCs that the AD780 is suited for is the AD7884, a 16-bit,
high speed sampling ADC (see Figure 21). This part previously
needed a precision 5 V reference, resistor divider, and buffer
amplifier to do this function.
Figure 18. Capacitive Load Transient Response Test Circuit
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Rev. J | 9 of 12
Data Sheet
AD780
APPLYING THE AD780
Figure 23. 4.5 V Reference from a Single 5 V Supply
Figure 21. Precision 3 V Reference for the AD7884 16-Bit, High Speed ADC
The AD780 is also ideal for use with higher resolution converters,
such as the AD7710/AD7711/AD7712 (see Figure 22). While these
parts are specified with a 2.5 V internal reference, the AD780 in 3
V mode can be used to improve the absolute accuracy, temperature
stability, and dynamic range. It is shown in Figure 22 with the two
optional noise reduction capacitors.
NEGATIVE (–2.5 V) REFERENCE
The AD780 can produce a negative output voltage in shunt mode
by connecting the input and output to ground, and connecting the
GND pin of the AD780 to a negative supply via a bias resistor, as
shown in Figure 25.
Figure 24. Negative (−2.5 V Shunt Mode Reference)
Figure 22. Precision 2.5 V or 3.0 V Reference for the AD7710 High Resolution,
Σ-Δ ADC
4.5 V REFERENCE FROM 5 V SUPPLY
A precise –2.5 V reference capable of supplying up to 100 mA to a
load can be implemented with the AD780 in series mode, using the
bootstrap circuit shown in Figure 25.
Some 5 V high resolution ADCs can accommodate reference voltages up to 4.5 V. The AD780 can be used to provide a precision
4.5 V reference voltage from a 5 V supply using the circuit shown
in Figure 23. This circuit provides a regulated 4.5 V output from a
supply voltage as low as 4.7 V. The high quality tantalum 10 µF
capacitor, in parallel with the ceramic AD780 0.1 µF capacitor and
the 3.9 Ω resistor, ensures a low output impedance around 50 MHz.
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Rev. J | 10 of 12
Data Sheet
AD780
APPLYING THE AD780
Figure 25. −2.5 V High Load Current Reference
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Rev. J | 11 of 12
Data Sheet
AD780
OUTLINE DIMENSIONS
Figure 26. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body (R-8)
Dimensions shown in millimeters and (inches)
Figure 27. 8-Lead Plastic Dual-In-Line Package [PDIP]
Narrow Body (N-8)
Dimensions shown in inches and (millimeters)
Updated: November 02, 2022
ORDERING GUIDE
Model1
Temperature Range
Package Description
AD780ANZ
AD780ARZ
AD780ARZ-REEL7
AD780BNZ
AD780BRZ
AD780BRZ-REEL
AD780BRZ-REEL7
AD780CRZ
AD780CRZ-REEL7
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
8-Lead PDIP
8-Lead SOIC
8-Lead SOIC
8-Lead PDIP
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
1
Packing Quantity
Reel, 1000
Reel, 2500
Reel, 750
Reel, 1000
Package
Option
N-8
R-8
R-8
N-8
R-8
R-8
R-8
R-8
R-8
Z = RoHS Compliant Part.
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registered trademarks are the property of their respective owners.
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Rev. J | 12 of 12
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