ad680.pdf

Low Power, Low Cost

2.5 V Reference

AD680*

FEATURES

Low Quiescent Current: 250

CONNECTION DIAGRAMS

A max

Laser Trimmed to High Accuracy:

2.5 V

5 mV max (AN, AR Grade)

Trimmed Temperature Coefficient:

20 ppm/

TP*

+V IN

TEMP

TP*

AD680

BOTTOM VIEW

(Not to Scale)

AD680

TP*

C max (AN, AR Grade)

Low Noise: 8

TOP VIEW

(Not to Scale)

V p-p from 0.1 Hz to 10 Hz

V OUT

Hz Wideband

Temperature Output Pin (N, R Packages)

Available in Three Package Styles:

8-Pin Plastic DIP, 8-Pin SOIC and 3-Pin TO-92

GND

+V IN

V OUT GND

NC = NO CONNECT

TP DENOTES FACTORY TEST POINT.

NO CONNECTIONS SHOULD BE MADE

TO THESE PINS.

PRODUCT DESCRIPTION

The AD680 is a bandgap voltage reference which provides a

fixed 2.5 V output from inputs between 4.5 V and 36 V. The

architecture of the AD680 enables the reference to be operated

at a very low quiescent current while still realizing excellent dc

characteristics and noise performance. Trimming of the high

stability thin-film resistors is performed for initial accuracy and

temperature coefficient, resulting in low errors over temperature.

The precision dc characteristics of the AD680 make it ideal for

use as a reference for D/A converters which require an external

precision reference. The device is also ideal for A/D converters

and, in general, can offer better performance than the standard

on-chip references.

Based upon the low quiescent current of the AD680, which

rivals that of many incomplete two-terminal references, the

AD680 is recommended for low power applications such as

hand-held battery equipment.

A temperature output pin is provided on the 8-pin package ver-

sions of the AD680. The temperature output pin provides an

output voltage that varies linearly with temperature and allows

the AD680 to be configured as a temperature transducer while

providing a stable 2.5 V output.

The AD680 is available in five grades. The AD680AN is speci-

fied for operation from –40

PRODUCT HIGHLIGHTS

1. The AD680 bandgap reference operates on a very low quies-

cent current which rivals that of many two-terminal refer-

ences. This makes the complete, higher accuracy AD680

ideal for use in power sensitive applications.

2. Laser trimming of both initial accuracy and temperature

coefficients results in low errors over temperature without the

use of external components. The AD680AN and AD680AR

have a maximum variation of 6.25 mV between –40°C and

+85°C.

3. The AD680 noise is low, typically 8 mV p-p from 0.1 Hz t o

10 Hz. Spectral density is also low, typically 250 nV/ÖHz.

4. The temperature output pin on the 8-pin package versions

enables the AD680 to be configured as a temperature trans-

ducer.

5. Plastic DIP packaging provides machine insertability, while

SOIC packaging provides surface mount capability. TO-92

packaging offers a cost effective alternative to two-terminal

references, offering a complete solution in the same package

in which two-terminal references are usually found.

C to +85

C, while the AD680JN

C operation. Both the AD680AN

and AD680JN are available in 8-pin plastic DIP packages. The

AD680AR is specified for operation from –40

C to +70

C to +85

C operation.

Both are available in an 8-pin Small Outline IC (SOIC) pack-

age. The AD680JT is specified for 0

C to +70

C operation and

is available in a 3-pin TO-92 package.

*Protected by U.S. Patent Nos. 4,902,959; 4,250,445 and 4,857,862.

REV. C

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.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 617/329-4700

Fax: 617/326-8703

250 nV/

is specified for 0

while the AD680JR is specified for 0

AD680–SPECIFICATIONS

AD680AN/AR

(T A = +25 8 C, V IN = +5 V, unless otherwise noted)

AD680JN/JR

AD680JT

Model

Min

Typ Max

Min

Typ

Max

Min

Typ

Max

Units

OUTPUT VOLTAGE

2.495

2.505

2.490

2.510 2.490

2.510

OUTPUT VOLTAGE DRIFT 1

0°C to +70°C

ppm/°C

–40°C to +85°C

LINE REGULATION

4.5 V £ +V IN £ 15 V

mV/V

(@ T MIN to T MAX )

15 V £ +V IN £ 36 V

(@ T MIN to T MAX )

LOAD REGULATION

0 < I OUT < 10 mA

100

mV/mA

(@ T MIN to T MAX )

100

QUIESCENT CURRENT

195 250

(@ T MIN to T MAX )

280

POWER DISSIPATION

1.25

OUTPUT NOISE

0.1 Hz to 10 Hz

mV p-p

Spectral Density, 100 Hz

250

nV/

CAPACITIVE LOAD

LONG TERM STABILITY

ppm/1000 hr

SHORT CIRCUIT CURRENT

TO GROUND

TEMPERATURE PIN

Voltage Output @ +25°C

540

596 660

Temperature Sensitivity

mV/°C

Output Current

–5

Output Resistance

TEMPERATURE RANGE

Specified Performance

–40

+85

+70

Operating Performance 2

–40

+85

–40

+85

–40

+85

NOTES

1 Maximum output voltage drift is guaranteed for all packages.

2 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.

*Same as AD680AN/AR specification.

Specifications subject to change without notice.

Specifications in boldface are tested on all production units at final eleetrical test. Results from those tests are used to calculate out going quality levels. All min and

max specifications are guaranteed.

–2–

REV. C

AD680

ABSOLUTE MAXIMUM RATINGS*

V IN to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 V

Power Dissipation (25°C) . . . . . . . . . . . . . . . . . . . . . . 500 mW

Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +125°C

Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . . 300°C

Package Thermal Resistance

q JA (All Packages) . . . . . . . . . . . . . . . . . . . . . . . . 120°C/W

Output Protection: Output safe for indefinite short to ground

and momentary short to V IN .

*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 sections of this specification is not implied. Exposure to absolute

maximum rating conditions for extended periods may affect device reliability.

THEORY OF OPERATION

Bandgap references are the high performance solution for low

supply voltage operation. A typical precision bandgap will con-

sist of a reference core and buffer amplifier. Based on a new,

patented bandgap reference design (Figure 2), the AD680

merges the amplifier and the core bandgap function to produce

a compact, complete precision reference. Central to the device

is a high gain amplifier with an intentionally large Proportional

To Absolute Temperature (PTAT) input offset. This offset is

controlled by the area ratio of the amplifier input pair, Q1 and

Q2, and is developed across resistor R1. Transistor Q12’s base

emitter voltage has a Complementary To Absolute Temperature

(CTAT) characteristic. Resistor R2 and the parallel combina-

tion of R3 and R4 “multiply” the PTAT voltage across R1.

Trimming resistors R3 and R4 to the proper ratio produces a

temperature invariant 2.5 V at the output. The result is an

accurate, stable output voltage accomplished with a minimum

number of components.

8-Pin Plastic DIP

and

8-Pin SOIC Packages

TP*

+V IN

AD680

TP*

TEMP

TOP VIEW

(Not to Scale)

V OUT

GND

Q11

V OUT

NC = NO CONNECT

TP DENOTES FACTORY TEST POINT.

NO CONNECTIONS SHOULD BE MADE

TO THESE PINS.

Q10

Q12

TO-92 Package

AD680

BOTTOM VIEW

(Not to Scale)

TEMP

GND

Figure 2. AD680 Schematic Diagram

+V IN

V OUT GND

An additional feature with this approach is the ability to mini-

mize the noise while maintaining very low overall power

dissipation for the entire circuit. Frequently it is difficult to

independently control the dominant noise sources for bandgap

references: bandgap transistor noise and resistor thermal noise.

By properly choosing the operating currents of Q1 and Q2 and

separately sizing R1, low wideband noise is realized while main-

taining 1 mW typical power dissipation.

Figure 1. Connection Diagrams

ORDERING GUIDE

Initial Temperature

Error Coeff.

Temperature

Package

Model

ppm/

Range

Description Option*

AD680JN 10

C to +70

Plastic

N-8

AD680JR 10

C to +70

SOIC

SO-8

AD680JT 10

C to +70

TO-92

AD680AN 5

–40

C to +85

Plastic

N-8

AD680AR 5

–40

C to +85

SOIC

SO-8

*N = Plastic DIP Package; SO = SOIC Package; T = TO-92 Package.

REV. C

–3–

AD680

APPLYING THE AD680

The AD680 is simple to use in virtually all precision reference

applications. When power is applied to +V IN and the GND pin

is tied to ground, V OUT provides a +2.5 V output. The AD680

typically requires less than 250 mA of current when operating

from a supply of +4.5 V to +36 V.

To operate the AD680, the +V IN pin must be bypassed to the

GND pin with a 0.1 mF capacitor tied as close to the AD680 as

possible. Although the ground current for the AD680 is small

(typically 195 mA), a direct connection should be made between

the AD680 GND pin and the system ground plane.

Reference outputs are frequently required to handle fast tran-

sients caused by input switching networks, as are commonly

found in ADCs and measurement instrumentation equipment.

Many of the dynamic problems associated with this situation

can be minimized with a few simple techniques. Using a series

resistor between the reference output and the load will tend to

“decouple” the reference output from the transient source. Or a

relatively large capacitor connected from the reference output to

ground can serve as a charge storage element to absorb and de-

liver charge as is required by the dynamic load. A 50 nF capaci-

tor is recommended for the AD680 in this case; this is large

enough to store the required charge, but small enough so as not

to disrupt the stability of the reference.

The 8-pin plastic DIP and SOIC packaged versions of the

AD680 also provide a temperature output pin. The voltage on

this pin is nominally 596 mV at 25°C. This pin will provide an

output linearly proportional to temperature with a characteristic

of 2 mV/°C.

Noise in a 300 kHz bandwidth is approximately 800 mV p-p.

Figure 4 shows the broadband noise of a typical AD680.

Figure 4. Broadband Noise at 300 kHz

TURN-ON TIME

Upon application of power (cold start), 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. Two components

normally associated with this are: the time for the active circuits

to settle, and the time for the thermal gradients on the chip to

stabilize. Figure 5 shows the turn-on settling time of the AD680

to be about 20

s to 0.025% of its final value.

NOISE PERFORMANCE

The noise generated by the AD680 is typically less than 8 mV

p-p over the 0.1 Hz to 10 Hz band. Figure 3 shows the 0.1 Hz

to 10 Hz noise of a typical AD680. The noise measurement is

made with a bandpass filter made of a 1-pole high-pass filter

with a corner frequency at 0.1 Hz and a 2-pole low-pass filter

with a corner frequency at 12.6 Hz to create a filter with a

9.922 Hz bandwidth.

Figure 5. Turn-On Settling Time

The AD680 thermal settling characteristic benefits from its

compact design. Once initial turn-on is achieved, the output lin-

early approaches its final value; the output is typically within

0.01% of its final value after 25 ms.

DYNAMIC PERFORMANCE

The output stage of the ampliflier is designed to provide the

AD680 with static and dynamic load regulation superior to less

complete references.

Figure 3. 0.1 Hz to 10 Hz Noise

–4–

REV. C

AD680

Figure 6 displays the characteristics of the AD680 output ampli-

fier driving a 0 mA to 10 mA load. Longer settling times will re-

sult if the reference is forced to sink any transient current.

In some applications, a varying load may be both resistive and

capacitive in nature, or the load may be connected to the

AD680 by a long capacitive cable.

Figure 7 displays the output amplifier characteristics driving a

1000 pF, 0 mA to 10 mA load.

+V IN

V OUT

0.1 m F

AD680

V OUT

+V IN

1000pF

249

V OUT

0.1

AD680

V L

249 W

V L

V OUT

Figure 7a. Capacitive Load Transient Response Test

Circuit

Figure 6a. Transient Load Test Circuit

Figure 7b. Output Response with Capacitive Load

Figure 6b. Large-Scale Transient Response

LOAD REGULATION

Figure 8 shows the load regulation characteristics of the AD680.

Figure 6c. Fine Scale Settling for Transient Load

Figure 8. Typical Load Regulation Characteristics

REV. C

–5–

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