AD680
ABSOLUTE MAXIMUM RATINGS*
THEORY OF OPERATION
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
θ
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.
8-Pin Plastic DIP
and
8-Pin SOIC Packages
TP*
+V
IN
TEMP
GND
1
2
3
4
NC = NO CONNECT
* TP DENOTES FACTORY TEST POINT.
NO CONNECTIONS SHOULD BE MADE
TO THESE PINS.
8
TP*
TP*
V
OUT
NC
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.
+V
IN
AD680
TOP VIEW
(Not to Scale)
7
6
5
Q9
Q8
Q11
Q3
Q1
1x
Q2
Q4
Q5
R1
R3
8x
C1
R2
Q12
V
OUT
R5
Q10
TO-92 Package
R6
Q6
Q7
AD680
BOTTOM VIEW
(Not to Scale)
3
+V
IN
2
V
OUT
1
GND
TEMP
R7
GND
R4
Figure 2. AD680 Schematic Diagram
Figure 1. Connection Diagrams
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
AD680JN
AD680JR
AD680JT
AD680AN
AD680AR
Initial
Error
mV
10
10
10
5
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
Package
Description
Plastic
SOIC
TO-92
Plastic
SOIC
Package
Option*
N-8
SO-8
TO-92
N-8
SO-8
*N = Plastic DIP Package; SO = SOIC Package; T = TO-92 Package.
REV. C
–3–
AD [ ANALOG DEVICES ]
