AD AD680JN Low power, low cost 2.5 v reference Datasheet

a
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
Low Power, Low Cost
2.5 V Reference
AD680*
CONNECTION DIAGRAMS
TP*
1
+VIN
2
TEMP
3
GND
4
8
TP*
AD680
AD680
7
TP*
BOTTOM VIEW
(Not to Scale)
TOP VIEW
(Not to Scale)
6
VOUT
5
NC
3
2
1
+VIN
VOUT
GND
NC = NO CONNECT
* TP DENOTES FACTORY TEST POINT.
NO CONNECTIONS SHOULD BE MADE
TO THESE PINS.
PRODUCT DESCRIPTION
PRODUCT HIGHLIGHTS
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.
1. The AD680 bandgap reference operates on a very low quiescent current which rivals that of many two-terminal references. This makes the complete, higher accuracy AD680
ideal for use in power sensitive applications.
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 versions 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.
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 transducer.
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.
The AD680 is available in five grades. The AD680AN is specified 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) package. 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
AD680–SPECIFICATIONS
(TA = +258C, VIN = +5 V, unless otherwise noted)
Model
AD680AN/AR
Min
Typ Max
Min
OUTPUT VOLTAGE
2.495
2.490
OUTPUT VOLTAGE DRIFT1
0°C to +70°C
–40°C to +85°C
2.505
10
2.510
10
25
20
LINE REGULATION
4.5 V ≤ +VIN ≤ 15 V
(@ TMIN to TMAX)
15 V ≤ +VIN ≤ 36 V
(@ TMIN to TMAX)
AD680JN/JR
Typ
Max
40
40
40
40
LOAD REGULATION
0 < IOUT < 10 mA
(@ TMIN to TMAX)
Min
AD680JT
Typ
Max
2.490
25
10
25
*
*
*
*
Units
2.510
V
30
ppm/°C
*
*
*
*
µV/V
80
80
100
100
*
*
*
*
*
*
*
*
µV/mA
QUIESCENT CURRENT
(@ TMIN to TMAX)
195
250
280
*
*
*
*
*
*
µA
POWER DISSIPATION
1
1.25
*
*
*
*
mW
OUTPUT NOISE
0.1 Hz to 10 Hz
Spectral Density, 100 Hz
8
250
10
*
*
*
*
*
*
mV p-p
nV/√Hz
*
nF
CAPACITIVE LOAD
50
*
LONG TERM STABILITY
25
SHORT CIRCUIT CURRENT
TO GROUND
25
50
596
2
660
*
+5
*
TEMPERATURE PIN
Voltage Output @ +25°C
Temperature Sensitivity
Output Current
Output Resistance
TEMPERATURE RANGE
Specified Performance
Operating Performance2
540
–5
*
12
–40
–40
*
*
*
*
*
*
*
ppm/1000 hr
*
mV
mV/°C
µA
kΩ
*
*
+85
+85
0
–40
+70
+85
mA
0
–40
+70
+85
°C
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*
THEORY OF OPERATION
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.
Bandgap references are the high performance solution for low
supply voltage operation. A typical precision bandgap will consist 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 combination 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.
*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
8
TP*
AD680
7
TP*
TOP VIEW
(Not to Scale)
6
VOUT
5
NC
+VIN
Q9
Q8
Q11
Q3
Q4
NC = NO CONNECT
Q1
1x
* TP DENOTES FACTORY TEST POINT.
NO CONNECTIONS SHOULD BE MADE
TO THESE PINS.
R1
R3
Q2
8x
R5
R2
Q12
C1
Q10
TO-92 Package
Q6
R6
AD680
TEMP
BOTTOM VIEW
(Not to Scale)
GND
3
2
1
+VIN
VOUT
GND
Q7
R4
R7
Figure 2. AD680 Schematic Diagram
An additional feature with this approach is the ability to minimize 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 maintaining 1 mW typical power dissipation.
Figure 1. Connection Diagrams
ORDERING GUIDE
Model
Initial
Error
mV
Temperature
Coeff.
ppm/°C
Temperature
Range
Package
Description
Package
Option*
AD680JN
AD680JR
AD680JT
AD680AN
AD680AR
10
10
10
5
5
25
25
30
20
20
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
Plastic
SOIC
TO-92
Plastic
SOIC
N-8
SO-8
TO-92
N-8
SO-8
*N = Plastic DIP Package; SO = SOIC Package; T = TO-92 Package.
REV. C
VOUT
Q5
–3–
AD680
APPLYING THE AD680
The 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.
Noise in a 300 kHz bandwidth is approximately 800 µV p-p.
Figure 4 shows the broadband noise of a typical AD680.
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 transients 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 deliver charge as is required by the dynamic load. A 50 nF capacitor 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.
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 µs to 0.025% of its final value.
NOISE PERFORMANCE
The 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 5. Turn-On Settling Time
The AD680 thermal settling characteristic benefits from its
compact design. Once initial turn-on is achieved, the output linearly 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 amplifier driving a 0 mA to 10 mA load. Longer settling times will result if the reference is forced to sink any transient current.
Figure 7 displays the output amplifier characteristics driving a
1000 pF, 0 mA to 10 mA load.
+V IN
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.
0.1 µF
+V IN
0.1 µF
VOUT
VOUT
AD680
CL
1000pF
VOUT
VOUT
AD680
249Ω
VL
VOUT
0V
249Ω
VL
Figure 7a. Capacitive Load Transient Response Test
Circuit
VOUT
0V
Figure 6a. Transient Load Test Circuit
Figure 7b. Output Response with Capacitive Load
LOAD REGULATION
Figure 6b. Large-Scale Transient Response
Figure 8 shows the load regulation characteristics of the AD680.
Figure 6c. Fine Scale Settling for Transient Load
REV. C
Figure 8. Typical Load Regulation Characteristics
–5–
AD680
TEMPERATURE PERFORMANCE
760
The AD680 is designed for reference applications where temperature performancc is important. Extensivc temperature testing and characterization ensures that the device’s performance is
maintained over the specified temperature range.
TEMP PIN VOLTAGE – mV
720
Some confusion exists in thc area of defining and specifying reference 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 manufacturers 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.
680
640
600
560
520
480
440
–50 –40 –30 –20 –10 0 10 20 30 40 50 60 70 80 90
TEMPERATURE – C
Figure 10. Temp Pin Transfer Characteristic
2.501
SLOPE = TC
VMAX – VMIN
=
(TMAX – TMIN ) x 2.5V x 10 –6
2.500
2.499
=
2.501 – 2.498
85 C – (–40 C) x 2.5V x 10 –6
= 9.6ppm/ C
2.498
–50
–30
20
40
–10 0
60
TEMPERATURE – C
80
100
Figure 9. Typical AD680AN/AP Temperature Drift
DIFFERENTIAL TEMPERATURE TRANSDUCER
Figure 11 shows a differential temperature transducer that can
be used to measure temperature changes in the AD680’s environment. This circuit operates from a +5 V supply. The temperature 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 temperature, resistors with low temperature coefficients, such as
metal film resistors, should be used.
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 output voltages measured over the operating temperature range.
+5V
+5V
2
VIN
0.1µF
The maximum height of thc box for the appropriate temperature 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 readings may vary depending upon the test equipment utilized.
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 amplifiers that have bias currents below this value.
7
3
OP-90
AD680
2
GND
4
6
∆V OUT
= 10mV/ C
∆T
4
RF
RB
1.69kΩ
1%
6.98kΩ
1%
RBP
100Ω
TEMPERATURE OUTPUT PIN
The 8-pin packaged versions of the AD680 provide a temperature 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.
TEMP 3
Figure 11. Differential Temperature Transducer
LOW POWER, LOW VOLTAGE REFERENCE FOR DATA
CONVERTERS
The 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 current (195 µA), combined with the completeness and accuracy of
the AD680 make it ideal for low power applications such as
handheld, battery operated meters.
–6–
REV. C
AD680
One such ADC that the AD680 is well suitcd for is the
AD7701. Figure 12a shows the AD680 used as the reference for
this converter. The AD7701 is a 16-bit A/D converter with
on-chip digital filtering intended for the measurement of wide
dynamic range, low frequency signals such as those representing
chemical, physical or biological processes. It contains a charge
balancing (sigma-delta) ADC, calibration microcontroller with
on-chip static RAM, a clock oscillator and a serial communicatlons port.
+4.5 V REFERENCE FROM A +5 V SUPPLY
The AD680 can be used to provide a low power, +4.5 V reference as shown in Figure 13. In addition to the AD680, the circuit uses a low power op amp and a transistor in a feedback
configuration that provides a regulated +4.5 V output for a
power supply voltage as low as +4.7 V. The high quality tantalum 10 µF capacitor (C1) in parallel with the ceramic 0.1 µF
capacitor (C2) and the 3.9 Ω resistor (R5) ensure a low output
impedance up to around 50 MHz.
This entire circuit runs on ± 5 V supplies. The power dissipation
of the AD7701 is typically 25 mW and, when combined with
the power dissipation of the AD680 (1 mW), the entire circuit
consumes just 26 mW of power.
+4.7V TO +15V
2N2907A
+V IN
VOUT
0.1µF
+5V
ANALOG
SUPPLY
OP-90
2
–IN
V IN
VOUT
VREF
RANGE
SELECT
BP/UP
DATA READY
CS
SCLK
READ (TRANSMIT)
R2
2.5k
1%
ANALOG
INPUT
A IN
ANALOG
GROUND
AGND
SERIAL DATA
Figure 13. +4.5 V Reference Running from a Single +5 V
Supply
CLKIN
CLKOUT
The AD680 is ideal for providing a stable, low cost and low
power reference voltage in portable equipment power supplies.
Figure 14 shows how the AD680 can be used in a voltage regulator that not only has low output noise (as compared to a
switchmode design) and low power, but also a very fast recovery
after current surges. Some precaution should be taken in the
selection of the output capacitors. Too high an ESR (effective
series resistance) could endanger the stability of the circuit. A
solid tantalum capacitor, 16 V or higher, and an aluminum electrolytic capacitor, 10 V or higher, are recommended for C1 and
C2, respectively. Also, the path from the ground side of C1 and
C2 to the ground side of R1 should be kept as short as possible.
DGND
AVSS
0.1µF
VOLTAGE REGULATOR FOR PORTABLE EQUIPMENT
SC1
SC2
0.1µF
0.1µF
DVSS
10µF
Figure 12a. Low Power, Low Voltage Supply Reference
for the AD7701 16-Bit A/D Converter
Figure 12b shows the AD680 connected to the AD773 high
speed 8-bit ADC. The low pass filter shown minimizes the
AD680’s wideband noise.
2
CHARGER
INPUT
V IN
AD680
0.1µF
2
22Ω
V OUT 6
GND
4
2k 1%
SERIAL CLOCK
CAL
CALIBRATE
2 REF IN
10µF
0.1µF
510kΩ
VIN
V OUT
6V
AD773
LEAD-ACID
BATTERY
1 REF GND
+
2
7
TEMP 3
3
4
AD680
The AD773’s high impedance reference input allows direct connection to the AD680. Unlike the resistor ladder requirements
of a flash converter the AD773’s single pin, high impedance input can be driven from one low cost, low power reference. The
high impedance input allows multiple AD773’s to be driven
from one AD680 thus minimizing drift errors.
IRF9530
6
GND
4
Figure 12b. AD680 to AD773 Connection
R3
6
OP-20
+5V, 1A
R2
R1
REV. C
0.1µF
R1
DRDY
SDATA
R5
3.9
0.1µF
MODE
AD7701
R4
3.57k
C2
0.1µF
CF
SLEEP
AD680
6
4
DV DD
GND
–5V
ANALOG
SUPPLY
OUT
+C1
10µF
V–
AV DD
0.1µF
+4.5V
V+
GND
10µF
7
+IN
3
AD680
0.1µF
CC
3.3µF
R3
1k
402kΩ
1%
402kΩ
1%
68µF
TANT
C1
+
+ 1000µF
ELECT
C2
Figure 14. Voltage Regulator for Portable Equipment
–7–
AD680
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Pin SOIC
3-Pin TO-92
0.198 (5.00)
8
5
0.280 (7.11)
1
4
0.135
(3.43)
MIN
0.188 (4.75)
0.240 (6.10)
5
8
0.210 (5.33)
0.170 (4.58)
0.158 (4.00)
0.430 (10.92)
0.348 (8.84)
0.150 (3.80)
0.060 (1.52)
0.015 (0.38)
0.210 (5.33)
MAX
0.244 (6.200)
0.228 (5.80)
0.70 (1.77)
SEATING PLANE
1
0.050 (1.27) MAX
4
0.150
(3.81)
MIN
0.018 (0.46)
0.022 (0.558)
0.014 (0.356)
0.205 (5.20)
0.175 (4.96)
C1503a–5–9/93
8-Pin Plastic DIP
0.050 (1.27)
TYP
0.100 BSC
(2.54 BSC)
0.014 (0.36)
0.500
(12.70)
MIN
0.019 (0.482)
0.016 (0.407)
SQUARE
0.045 (1.15)
0.325 (8.25)
0.195
(4.95)
MAX
0.300 (7.62)
0.069 (1.75)
0.053 (1.35)
0.010 (0.25)
0.004 (0.10)
0.205 (5.20)
0.181 (4.60)
0.015 (0.381)
0.055 (1.39)
0.045 (1.15)
0.008 (0.204)
0.105 (2.66)
0.095 (2.42)
0.015 (0.38)
0.007 (0.18)
0.045 (1.15)
0.020 (0.50)
0.105 (2.66)
0.080 (2.42)
0.165 (4.19)
0.125 (3.94)
PRINTED IN U.S.A.
0.105 (2.66)
0.080 (2.42)
–8–
REV. C
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