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AD680
(Rev.:RevC)

Low Power, Low Cost 2.5 V Reference

Analog Devices 

AD680

ABSOLUTE MAXIMUM RATINGS*

VIN 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

θJA (All Packages) . . . . . . . . . . . . . . . . . . . . . . . . 120°C/W

Output Protection: Output safe for indefinite short to ground

and momentary short to VIN.

*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.

8-Pin Plastic DIP

and

8-Pin SOIC Packages

TP* 1

+VIN 2

TEMP 3

GND 4

AD680

TOP VIEW

(Not to Scale)

8 TP*

7 TP*

6 VOUT

5 NC

NC = NO CONNECT

* TP DENOTES FACTORY TEST POINT.

NO CONNECTIONS SHOULD BE MADE

TO THESE PINS.

TO-92 Package

AD680

BOTTOM VIEW

(Not to Scale)

3

+VIN

2

VOUT

1

GND

Figure 1. Connection Diagrams

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.

+VIN

Q9

Q8

R5

Q10

Q3

Q4

Q1

1x

Q2

8x

Q5

C1

R1

R2

Q12

Q11

VOUT

R3

TEMP

GND

R6

Q6

Q7

R7

R4

Figure 2. AD680 Schematic Diagram

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.

ORDERING GUIDE

Model

Initial

Error

mV

AD680JN 10

AD680JR 10

AD680JT 10

AD680AN 5

AD680AR 5

Temperature

Coeff.

ppm/°C

25

25

30

20

20

Temperature

Range

0°C to +70°C

0°C to +70°C

0°C to +70°C

–40°C to +85°C

–40°C to +85°C

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

Package

Description

Plastic

SOIC

TO-92

Plastic

SOIC

Package

Option*

N-8

SO-8

TO-92

N-8

SO-8

REV. C

–3–

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