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Data Sheet

AD780

2.5 V/3.0 V High Precision Reference

Rev. J

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FEATURES

► 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)

FUNCTIONAL BLOCK DIAGRAM

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-to-

analog 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.

A temperature output pin on the AD780 provides an output voltage

that varies linearly with temperature, allowing the part to be config-

ured 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.

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 coeffi-

cients 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.

Summary of content (12 pages)

PAGE 1
Data Sheet AD780 2.5 V/3.0 V High Precision Reference FEATURES ► ► ► ► ► ► ► ► ► ► 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.
PAGE 2
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...........................................
PAGE 3
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.
PAGE 4
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.
PAGE 5
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.
PAGE 6
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.
PAGE 7
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.
PAGE 8
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.
PAGE 9
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.
PAGE 10
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.
PAGE 11
Data Sheet AD780 APPLYING THE AD780 Figure 25. −2.5 V High Load Current Reference analog.com Rev.
PAGE 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.