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AD680AN-AD680AR-AD680JN-AD680JN.-AD680JR-AD680JT
Low Power, Low Cost 2.5 V Reference
CONNECTION DIAGRAMSREV.C
Low Power, Low Cost
2.5 V Reference
FEATURES
Low Quiescent Current: 250 mA max
Laser Trimmed to High Accuracy:
2.5 V 65 mV max (AN, AR Grade)
Trimmed Temperature Coefficient:
20 ppm/8C max (AN, AR Grade)
Low Noise: 8 mV p-p from 0.1 Hz to 10 Hz
250 nV/√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
PRODUCT DESCRIPTIONThe 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°C to +85°C, while the AD680JN
is specified for 0°C to +70°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 +85°C,
while the AD680JR is specified for 0°C to +70°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.
*. Patent Nos. 4,902,959; 4,250,445 and 4,857,862.
PRODUCT HIGHLIGHTS1. 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 μV p-p from 0.1 Hz to
10 Hz. Spectral density is also low, typically 250 nV/√Hz.
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.
AD680–SPECIFICATIONSLINE REGULATION
LOAD REGULATION
QUIESCENT CURRENT
TEMPERATURE PIN
TEMPERATURE RANGE
NOTESMaximum output voltage drift is guaranteed for all packages.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 outgoing quality levels. All min and
max specifications are guaranteed.
(TA = +258C, VIN = +5 V, unless otherwise noted)
THEORY OF OPERATIONBandgap 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.
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
TO-92 PackageFigure 1. Connection Diagrams
ORDERING GUIDE
AD680
APPLYING THE AD680The AD680 is simple to use in virtually all precision reference
applications. When power is applied to +VIN and the GND pin
is tied to ground, VOUT provides a +2.5 V output. The AD680
typically requires less than 250 μA of current when operating
from a supply of +4.5 V to +36 V.
To operate the AD680, the +VIN pin must be bypassed to the
GND pin with a 0.1 μF capacitor tied as close to the AD680 as
possible. Although the ground current for the AD680 is small
(typically 195 μA), 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 PERFORMANCEThe noise generated by the AD680 is typically less than 8 μV
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 3.0.1 Hz to 10 Hz Noise
Noise in a 300 kHz bandwidth is approximately 800 μV p-p.
Figure 4 shows the broadband noise of a typical AD680.
Figure 4.Broadband Noise at 300 kHz
TURN-ON TIMEUpon 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 μs to 0.025% of its final value.
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 PERFORMANCEThe output stage of the ampliflier is designed to provide the
AD680 with static and dynamic load regulation superior to less
complete references.
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.
IN
249WL0VOUT0.1 mFOUTFigure 6a.Transient Load Test Circuit
Figure 6b.Large-Scale Transient Response
Figure 6c.Fine Scale Settling for Transient Load
Figure 7 displays the output amplifier characteristics driving a
1000 pF, 0 mA to 10 mA load.
1000pF249WL0VOUTOUTIN
0.1 mFFigure 7a.Capacitive Load Transient Response Test
Circuit
Figure 7b.Output Response with Capacitive Load
LOAD REGULATIONFigure 8 shows the load regulation characteristics of the AD680.
Figure 8.Typical Load Regulation Characteristics
AD680
TEMPERATURE PERFORMANCEThe AD680 is designed for reference applications where tem-
perature performancc is important. Extensivc temperature test-
ing and characterization ensures that the device’s performance is
maintained over the specified temperature range.
Some confusion exists in thc area of defining and specifying ref-
erence voltage error over temperature. Historically, references
have been characterized using a maximum deviation per degree
centigrade, i.e., ppm/°C. However, because of nonlinearities in
temperature characteristics which originated in standard Zener
references (such as “S” type characteristics), most manufactur-
ers now use a maximum limit error band approach to specify
devices. This technique involves the measurement of the output
at three or more different temperatures to specify an output
voltage error band.
V – VMAXMIN(T – T ) x 2.5V x 10MAXMIN
2.501 – 2.498
85 C – (–40 C) x 2.5V x 10–6
TEMPERATURE – CFigure 9.Typical AD680AN/AP Temperature Drift
Figure 9 shows a typical output voltage drift for the AD680AN/
AR and illustrates the test methodology. The box in Figure 9 is
bounded on the sides by the operating temperature extremes,
and on the top and bottom by the maximum and minimum out-
put voltages measured over the operating temperature range.
The maximum height of thc box for the appropriate tempera-
ture range and device grade is shown in Table I. Duplication of
these results requires a combination of high accuracy and stable
temperature control in a test system. Evaluation of the AD680
will produce a curve similar to that in Figure 9, but output read-
ings may vary depending upon the test equipment utilized.
TEMPERATURE OUTPUT PINThe 8-pin packaged versions of the AD680 provide a tempera-
ture output pin on Pin 3 of each device. The output of Pin 3
(TEMP) is a voltage that varies linearly with temperature.
VTEMP at 25°C is 596 mV, and the temperature coefficient is
2 mV/°C. Figure 10 shows the output of this pin over
temperature.
The temperature pin has an output resistance of 12 kΩ and is
capable of sinking or sourcing currents of up to 5 μA without
disturbing the reference output, enabling the temp pin to be
buffered by any of a number of inexpensive operational amplifi-
ers that have bias currents below this value.
Figure 10.Temp Pin Transfer Characteristic
DIFFERENTIAL TEMPERATURE TRANSDUCERFigure 11 shows a differential temperature transducer that can
be used to measure temperature changes in the AD680’s envi-
ronment. This circuit operates from a +5 V supply. The tem-
perature dependent voltage from the TEMP pin of the AD680
is amplified by a factor of 5 to provide wider full-scale range and
more current sourcing capability. An exact gain of 5 can be
achieved by adjusting the trim potentiometer until the output
varies by 10 mV/°C. To minimize resistance changes with tem-
perature, resistors with low temperature coefficients, such as
metal film resistors, should be used.
+5V
+5VF
1.69kW
6.98kW
0.1mF= 10mV/ COUTD
VTFigure 11.Differential Temperature Transducer
LOW POWER, LOW VOLTAGE REFERENCE FOR DATA
CONVERTERSThe AD680 has a number of features that make it ideally suited
for use with A/D and D/A converters. The low supply voltage
required makes it possible to use the AD680 with today’s
convertcrs that run on 5 V supplies without having to add a
higher supply voltage for the reference. The low quiescent cur-
rent (195 μA), combined with the completeness and accuracy of
the AD680 make it ideal for low power applications such as
handheld, battery operated meters.
