Analog Devices AD737 f Datasheet
Low Cost, Low Power,
FEATURES
Computes:
True rms value
Average rectified value
Absolute value
Provides:
200 mV full-scale input range
(larger inputs with input attenuator)
Direct interfacing with 3 1/2 digit CMOS ADCs
High input impedance: 10
Low input bias current: 25 pA max
High accuracy: ±0.2 mV ± 0.3% of reading
RMS conversion with signal crest factors up to 5
Wide power supply range: ±2.5 V to ±16.5 V
Low power: 160 µA max supply current
No external trims needed for specified accuracy
AD736—a general-purpose, buffered voltage output
version also available
GENERAL DESCRIPTION
The AD7371 is a low power, precision, monolithic true rms-todc converter. It is laser trimmed to provide a maximum error of
±0.2 mV ± 0.3% of reading with sine wave inputs. Furthermore,
it maintains high accuracy while measuring a wide range of
input waveforms, including variable duty-cycle pulses and triac
(phase) controlled sine waves. The low cost and small physical
size of this converter make it suitable for upgrading the
performance of non-rms precision rectifiers in many applications. Compared to these circuits, the AD737 offers higher
accuracy at equal or lower cost.
The AD737 can compute the rms value of both ac and dc input
voltages. It can also be operated ac-coupled by adding one
external capacitor. In this mode, the AD737 can resolve input
signal levels of 100 µV rms or less, despite variations in temperature or supply voltage. High accuracy is also maintained for
input waveforms with crest factors of 1 to 3. In addition, crest
factors as high as 5 can be measured (while introducing only
2.5% additional error) at the 200 mV full-scale input level.
The AD737 has no output buffer amplifier, thereby significantly
reducing dc offset errors occurring at the output, which makes
the device highly compatible with high input impedance ADCs.
______________________________________
1
Protected under U.S. Patent Number 5,495,245.
12
Ω
True RMS-to-DC Converter
AD737
FUNCTIONAL BLOCK DIAGRAM
8kΩ
1
C
C
V
2
POWER
DOWN
–V
IN
3
4
S
INPUT
AMPLIFIER
BIAS
SECTION
Figure 1.
Requiring only 160 µA of power supply current, the AD737 is
optimized for use in portable multimeters and other batterypowered applications. This converter also provides a powerdown feature that reduces the power-supply standby current to
less than 30 µA.
Two signal input terminals are provided in the AD737. A high
12
impedance (10
Ω) FET input interfaces directly with high R
input attenuators, and a low impedance (8 kΩ) input accepts
rms voltages to 0.9 V while operating from the minimum power
supply voltage of ±2.5 V. The two inputs can be used either
single-ended or differentially.
The AD737 achieves 1% of reading error bandwidth, exceeding
10 kHz for input amplitudes from 20 mV rms to 200 mV rms
while consuming only 0.72 mW.
The AD737 is available in four performance grades. The
AD737J and AD737K grades are rated over the commercial
temperature range of 0°C to 70°C. The AD737JR-5 is tested with
supply voltages of ±2.5 V dc. The AD737A and AD737B grades
are rated over the industrial temperature range of −40°C to
+85°C. The AD737 is available in three low cost, 8-lead
packages: PDIP, SOIC, and CERDIP.
PRODUCT HIGHLIGHTS
1. The AD737 is capable of computing the average rectified
value, absolute value, or true rms value of various input
signals.
2. Only one external component, an averaging capacitor, is
required for the AD737 to perform true rms measurement.
3. The low power consumption of 0.72 mW makes the
AD737 suitable for battery-powered applications.
AD737
FULL
WAVE
RECTIFIER
RMS CORE
8kΩ
8
COM
+V
7
6
OUTPUT
C
5
S
AV
00828-001
Rev. F
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 that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.326.8703 © 2005 Analog Devices, Inc. All rights reserved.
www.analog.com
AD737
TABLE OF CONTENTS
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 5
ESD Caution.................................................................................. 5
Pin Configurations and Function Descriptions ........................... 6
Typical Performance Characteristics ............................................. 7
Calculating Settling Time.......................................................... 10
Types of AC Measurement ........................................................ 10
Theory of Operation ...................................................................... 12
Rapid Settling Times via the Average Responding
Connection
DC Error, Output Ripple, and Averaging Error ..................... 13
Ac Measurement Accuracy and Crest Factor ......................... 13
Selecting Practical Values for Capacitors................................ 13
Application Circuits....................................................................... 15
Outline Dimensions....................................................................... 17
Ordering Guide .......................................................................... 18
................................................................................. 12
RMS Measurement—Choosing Optimum Value For C
AV
.... 12
REVISION HISTORY
1/05—Rev. E to Rev. F
Updated Format..................................................................Universal
Added Functional Block Diagram.................................................. 1
Changes to General Description Section ...................................... 1
Changes to Pin Configurations and Function
Descriptions Section .................................................................... 6
Changes to Typical Performance Characteristics Section........... 7
Changes to Table 4.......................................................................... 11
Change to Figure 24 ....................................................................... 12
Change to Figure 27 ....................................................................... 15
Changes to Ordering Guide.......................................................... 18
6/03—Rev. D to Rev. E
Added AD737JR-5..............................................................Universal
Changes to FEATURES ................................................................... 1
Changes to GENERAL DESCRIPTION ....................................... 1
Changes to SPECIFICATIONS....................................................... 2
Changes to ABSOLUTE MAXIMUM RATINGS ........................ 4
Changes to ORDERING GUIDE ................................................... 4
Added TPCs 16 through 19............................................................. 6
Changes to Figures 1 and 2.............................................................. 8
Changes to Figure 8........................................................................ 11
Updated OUTLINE DIMENSIONS ............................................ 12
12/02—Rev. C to Rev. D
Changes to FUNCTIONAL BLOCK DIAGRAM ........................ 1
Changes to PIN CONFIGURATION .............................................4
Figure 1 replaced ...............................................................................8
Changes to Figure 2...........................................................................8
Figure 5 replaced ............................................................................ 10
Changes to Application Circuits Figures 4, 6–8 ......................... 10
OUTLINE DIMENSIONS updated............................................. 12
12/99—Rev. B to Rev. C
Rev. F | Page 2 of 20
AD737
(
SPECIFICATIONS
T = 25°C, ±5 V supplies, except AD737J-5, ±2.5 V, CAV = 33 µF, CC = 10 µF, f = 1 kHz, sine wave input applied to Pin 2, unless otherwise
specified. Specifications shown in boldface are tested on all production units at final electrical test. Results from these tests are used to
calculate outgoing quality levels.
Table 1.
AD737J/AD737A AD737K/AD737B AD737J-5
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max Unit
TRANSFER FUNCTION
OUT
2
VAvgV =
IN
)
CONVERSION ACCURACY
Total Error EIN = 0 to 200 mV rms 0.2/0.3
0.4/0.5
±VS = ±2.5 V 0.2/0.3
±VS = ±2.5 V, Input to
0.2/0.3
0.2/0.2
0.2/0.3
±mV/±POR
0.4/0.5
0.4/0.5
Pin 1
E
T
to T
MIN
MAX
A and B Grades EIN = 200 mV rms
J and K Grades EIN = 200 mV rms,
= 200 mV − 1 V rms −1.2
IN
±2.0
−1.2
±2.0
POR
0.5/0.7
0.3/0.5
±mV/POR
0.007 0.007 0.02 ±POR/°C
±V
= ±2.5 V
S
vs. Supply Voltage EIN = 200 mV rms
±VS = ±2.5 V to ±5 V
±VS = ±5 V to ±16.5 V
DC Reversal Error,
VIN = 600 mV dc
0
0
−0.18
0.06
−0.3 0
0.1 0
−0.18
0.06
−0.3 0
0.1 0
−0.18
0.06
−0.3
0.1
1.3 2.5 1.3 2.5 POR
DC-Coupled
V
Nonlinearity
2
E
Input to Pin 1,
AC-Coupled
3
Total Error, External
= 200 mV dc,
IN
±V
= ±2.5 V
S
EIN = 0 to 200 mV rms
= 100 mV rms
IN
EIN = 100 mV rms, after
correction, ±V
= ±2.5 V
S
0
0.02 0.1 POR
1.7 2.5 POR
0.25
0.35
0 0.25
0.35
POR
EIN = 0 to 200 mV rms 0.1/0.2 0.1/0.2 0.1/0.2 ±mV/±POR
Trim
ADDITIONAL CREST FACTOR ERROR
4
Crest Factor = 1 to 3 CAV = CF = 100 µF 0.7 0.7 %
C
= 22 µF, CF =
AV
100 µF, ±V
= ±2.5 V,
S
1.7 %
input to Pin 1
Crest Factor = 5 CAV = CF = 100 µF 2.5 2.5 %
INPUT CHARACTERISTICS
High Z Input (Pin 2)
Signal Range
Continuous RMS
±VS = +2.5 V
200
Level
±VS = +2.8 V, −3.2 V
Peak Transient Input ±VS = +2.5 V, input to
±VS = ±5 V to ±16.5 V
200
1
200
1
mV rms
V rms
V
±0.6
Pin 1
±VS = +2.8 V, −3.2 V
±0.9
±0.9
V
±VS = ±5 V ±2.7 ±2.7 V
±VS = ±16.5 V
±4.0
Input Resistance 10
12
10
±4.0
12
V
10
12
Ω
Input Bias Current ±VS = ±5 V 1 25 1 25 1 25 pA
Low Z Input (Pin 1)
Signal Range
Continuous RMS
±VS = +2.5 V 300 mV rms
Level
±VS = +2.8 V, −3.2 V 300 300 mV rms
±VS = ±5 V to ±16.5 V 1 1 V rms
1
POR
POR
%/V
%/V
mV rms
Rev. F | Page 3 of 20
AD737
AD737J/AD737A AD737K/AD737B AD737J-5
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max Unit
Peak Transient Input ±VS = +2.5 V ±1.7 V
±VS = +2.8 V, −3.2 V ±1.7 ±1.7 V
±VS = ±5 V ±3.8 ±3.8 V
±VS = ±16.5 V ±11 ±11 V
Input Resistance 6.4 8 9.6 6.4 8 9.6 6.4 8 9.6 kΩ
Maximum Continuous
Nondestructive Input,
All Supply Voltages
Input Offset Voltage
vs. Temperature 8 30 8 30 8 30 µV/°C
vs. Supply VS = ±2.5 V to ±5 V 80 80 80 µV/V
V
OUTPUT CHARACTERISTICS—NO LOAD
Output Voltage Swing ±VS = +2.8 V, −3.2 V −1.6 −1.7 −1.6 −1.7 V
±VS = ±5 V −3.3 −3.4 −3.3 −3.4 V
±VS = ±16.5 V
±VS = ±2.5 V (Pin 1) −1.1 –0.9 V
Output Resistance dc 6.4 8 9.6 6.4 8 9.6 6.4 8 9.6 kΩ
FREQUENCY RESPONSE
High Impedance Input
(Pin 2)
1% Additional Error VIN = 1 mV rms 1 1 1 kHz
V
V
V
3 dB Bandwidth VIN = 1 mV rms 5 5 5 kHz
V
V
V
Low Z Input (Pin 1)
1% Additional Error VIN = 1 mV rms 1 1 1 kHz
V
V
V
V
3 dB Bandwidth VIN = 1 mV rms 5 5 5 kHz
V
V
V
POWER-DOWN
Disable Voltage 0 0 V
Input Current, PD
Enabled
POWER SUPPLY
Operating Voltage
Range
Current No input 120
Rated iInput 170 210 170 210 170 210 µA
Power-down 25 40 25 40 25 40 µA
TEMPERATURE RANGE See the Ordering Guide
1
POR = % of reading.
2
Nonlinearity is defined as the maximum deviation (in percent error) from a straight line connecting the readings at 0 V and 200 mV rms.
3
After fourth-order error correction using the equation y = − 0.31009x 4 − 0.21692x3 − 0.06939x2 + 0.99756x + 11.1 × 10−6, where y is the corrected result and x is the
device output between 0.01 V and 0.3 V.
4
Crest factor error is specified as the additional error resulting from the specific crest factor, using a 200 mV rms signal as a reference. The crest factor is defined as
/V rms.
V
PEAK
5
DC offset does not limit ac resolution.
±12 ±12 ±12 V p-p
5
AC-coupled
= ±5 V to ±16.5 V 50 150 50 150 µV/V
S
−4 −5
±3
−4 −5
±3
±3
mV
V
= 10 mV rms 6 6 6 kHz
IN
= 100 mV rms 37 37 37 kHz
IN
= 200 mV rms 33 33 33 kHz
IN
= 10 mV rms 55 55 55 kHz
IN
= 100 mV rms 170 170 170 kHz
IN
= 200 mV rms 190 190 190 kHz
IN
= 10 mV rms 6 6 6 kHz
IN
= 40 mV rms 25 kHz
IN
= 100 mV rms 90 90 90 kHz
IN
= 200 mV rms 90 90 90 kHz
IN
= 10 mV rms 55 55 55 kHz
IN
= 100 mV rms 350 350 350 kHz
IN
= 200 mV rms 460 460 460 kHz
IN
VPD = V
S
+2.8/
11 11 µA
−3.2
±5 ±16.5 +2.8/
−3.2
160
120
±5 ±16.5 ±2.5 ±5 ±16.5 V
160
120
160
µA
Rev. F | Page 4 of 20
AD737
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
Supply Voltage ±16.5 V
Internal Power Dissipation
Input Voltage ±V
1
200 mW
S
Output Short-Circuit Duration Indefinite
Differential Input Voltage +VS and −V
S
Storage Temperature Range (Q) −65°C to +150°C
Storage Temperature Range (N, R) −65°C to +125°C
Lead Temperature Range (Soldering 60 sec) 300°C
ESD Rating 500 V
1
8-Lead PDIP package: θJA = 165°C/W.
8-Lead CERDIP package: θ
8-Lead SOIC: θ
= 155°C/W.
JA
= 110°C/W.
JA
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Rev. F | Page 5 of 20
AD737
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
1
C
C
AD737
2
V
IN
–V
3
4
S
TOP VIEW
(Not to Scale)
POWER DOWN
Figure 2. R-8 (SOIC) Pin Configuration
Table 3. Pin Function Descriptions
Pin No. Mnemonic Description
1 C
2 V
C
IN
3 POWER DOWN Disables the AD737. Low is enabled; high is powered-down.
4
5 C
−V
S
AV
6 OUTPUT Output.
7 +V
S
8 COM Common.
8
COM
7
+V
6
OUTPUT
5
C
S
AV
00828-029
POWER DOWN
C
V
–V
1
C
2
IN
3
4
S
AD737
TOP VIEW
(Not to Scale)
Figure 3. Q-8 (CERDIP) Pin Configuration
Coupling Capacitor for Indirect DC Coupling.
RMS Input.
Negative Power Supply.
Averaging Capacitor.
Positive Power Supply.
8
COM
+V
7
S
6
OUTPUT
C
5
AV
00828-030
1
C
C
AD737
2
V
IN
TOP VIEW
POWER DOWN
–V
3
4
S
(Not to Scale)
Figure 4. N-8 (PDIP) Pin Configuration
8
COM
+V
7
6
OUTPUT
C
5
S
AV
00828-031
Rev. F | Page 6 of 20
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