ANALOG DEVICES AD737 Service Manual
Low Cost, Low Power,
www.BDTIC.com/ADI
FEATURES
Computes
True rms value
Average rectified value
Absolute value
Provides
200 mV full-scale input range (larger inputs with
input a
ttenuator)
Direct interfacing with 3½ digit CMOS ADCs
High input impedance: 10
Low input bias current: 25 pA maximum
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 maximum supply current
No external trims needed for specified accuracy
A general-purpose, buffered voltage output version also
a
vailable (AD736)
GENERAL DESCRIPTION
The AD7371 is a low power, precision, monolithic true rms-to-dc
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 nonrms 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
v
oltages. 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
r
educing dc offset errors occurring at the output, which makes
the device highly compatible with high input impedance ADCs.
Requiring only 160 µA of power supply current, the AD737 is
ptimized for use in portable multimeters and other battery-
o
powered applications. This converter also provides a power-down
feature that reduces the power-supply standby current to less
than 30 µA.
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
AMPLIFI ER
BIAS
SECTION
Figure 1.
Two signal input terminals are provided in the AD737. A high
12
im
pedance (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
z for input amplitudes from 20 mV rms to 200 mV rms,
10 kH
while consuming only 0.72 mW.
The AD737 is available in four performance grades. The
AD737J an
d 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,
8lead packages: PDIP, SOIC_N, and CERDIP.
PRODUCT HIGHLIGHTS
1. Capable of computing the average rectified value, absolute
value, or true rms value of various input signals.
2. Onl
3. The lo
y one external component, an averaging capacitor, is
required for the AD737 to perform true rms measurement.
w power consumption of 0.72 mW makes the
AD737 suitable for battery-powered applications.
AD737
FULL-WAVE
RECTIFI ER
RMS CORE
8kΩ
8
COM
+V
7
6
OUTPUT
C
5
S
AV
00828-001
Rev. G
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her
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 www.analog.com
Fax: 781.461.3113 ©2006 Analog Devices, Inc. All rights reserved.
AD737
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TABLE OF CONTENTS
Features.............................................................................................. 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 1
Product Highlights ........................................................................... 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 6
Thermal Resistance ...................................................................... 6
ESD Caution.................................................................................. 6
Pin Configurations and Function Descriptions ........................... 7
Typical Performance Characteristics ............................................. 8
Theory of Operation ...................................................................... 12
Types of AC Measurement ........................................................ 12
DC Error, Output Ripple, and Averaging Error..................... 13
AC Measurement Accuracy and Crest Factor........................ 13
Calculating Settling Time.......................................................... 13
Applications..................................................................................... 14
RMS Measurement—Choosing Optimum Value for C
Rapid Settling Times via the Average Responding
Connection.................................................................................. 14
Selecting Practical Values for Capacitors ................................ 14
Scaling Input and Output Voltages.......................................... 14
AD737 Evaluation Board............................................................... 18
Outline Dimensions....................................................................... 20
Ordering Guide .......................................................................... 21
..... 14
AV
REVISION HISTORY
12/06—Rev. F to Rev. G
Changes to Specifications................................................................ 3
Reorganized Typical Performance Characteristics ...................... 8
Changes to Figure 21...................................................................... 11
Reorganized Theory of Operation Section ................................. 12
Reorganized Applications Section................................................ 14
Added Scaling Input and Output Voltages Section.................... 14
Deleted Application Circuits Heading......................................... 16
Changes to Figure 28...................................................................... 16
Added AD737 Evaluation Board Section .................................... 18
Updated Outline Dimensions....................................................... 20
Changes to Ordering Guide.......................................................... 21
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
D
escriptions 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. G | Page 2 of 24
AD737
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SPECIFICATIONS
TA = 25°C, ±VS = ±5 V except as noted, 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.
AD737A, AD737J AD737B, AD737K AD737J-5
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max Unit
ACCURACY
Total Error EIN = 0 to 200 mV rms 0.2/0.3
±VS = ±2.5 V 0.2/0.3
±VS = ±2.5 V,
E
Over Temperature
AQ and BQ EIN = 200 mV rms
JN, JR, KN, KR EIN = 200 mV rms,
AN and AR EIN = 200 mV rms,
Vs. Supply
Voltage
E
E
DC Reversal Error DC coup led,
V
Nonlinearity
Input to Pin 1
Total Error,
External Trim
ADDITIONAL
CREST FACTOR
4
ERROR
For Crest Factors
from 1 to 3
C
For Crest Factors
from 3 to 5
INPUT
CHARACTERISTICS
High-Z Input (Pin 2)
Signal Range
Continuous
RMS Level
±VS = +2.8 V/−3.2 V
±VS = ±5 V to ±16.5 V
input to Pin 1
= 200 mV to 1 V rms −1.2
IN
= ±2.5 V
±V
S
= ±2.5 V
±V
S
= 200 mV rms,
IN
= ±2.5 V to ±5 V
±V
S
= 200 mV rms,
IN
= ±5 V to ±16.5 V
±V
S
= 600 mV dc
V
IN
= 200 mV dc,
IN
= ±2.5 V
±V
2
3
S
EIN = 0 to 200 mV rms,
@ 100 mV rms
AC coupled,
= 100 mV rms, after
E
IN
correction, ±V
EIN = 0 to 200 mV rms 0.1/0.2 0.1/0.2 0.1/0.2 ±mV/±POR
CAV = CF = 100 μF 0.7 0.7 %
= 22 μF, CF = 100 μF,
AV
±V
= ±2.5 V,
S
input to Pin 1
CAV = CF = 100 μF 2.5 2.5 %
±VS = +2.5 V
= ±2.5 V
S
0.2/0.3
0.007 0.007 0.02 ±POR/°C
0.014 0.014 ±POR/°C
0
0
1.3 2.5 1.3 2.5 POR
1.7 2.5 POR
0
0.02 0.1 POR
1.7 %
−0.18
0.06
0.25
0.4/0.5
±2.0
0.5/0.7
−0.3 0
0.1 0
0.35 0
200
1
0.2/0.2
−1.2
−0.18
0.06
0.25
0.2/0.3
±2.0
0.3/0.5
−0.3 0
0.1 0
0.35
200
1
±mV/±POR
0.4/0.5
0.4/0.5
POR
±POR/°C
−0.18
0.06
POR
mV rms
V rms
−0.3
0.1
200
POR
POR
%/V
%/V
mV rms
1
Rev. G | Page 3 of 24
AD737
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AD737A, AD737J AD737B, AD737K AD737J-5
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max Unit
Peak Transient
Input
±VS = +2.8 V/−3.2 V
±VS = ±5 V ±2.7 ±2.7 V
±VS = ±16.5 V
Input Resistance 1012 1012 1012 Ω
Input Bias
Current
Low-Z Input
(Pin 1) Signal
Range
Continuous
RMS Level
±VS = +2.8 V/−3.2 V 300 300 mV rms
±VS = ±5 V to ±16.5 V 1 1 V rms
Peak Transient
Input
±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
Input Offset
5
Voltage
Over the Rated
Operating
Temperature
Range
Vs. Supply VS = ±2.5 V to ±5 V 80 80 80 μV/V
V
OUTPUT
CHARACTERISTICS
Output Voltage
Swing
±VS = ±5 V −3.3 −3.4 −3.3 −3.4 V
±VS = ±16.5 V
±VS = ±2.5 V, input
Output
Resistance
FREQUENCY
RESPONSE
High-Z Input
(Pin 2)
1% Additional
Error
V
V
V
= +2.5 V
±V
S
input to Pin 1
±VS = ±5 V 1 25 1 25 1 25 pA
±VS = +2.5 V 300 mV rms
±VS = +2.5 V ±1.7 V
All supply voltages ±12 ±12 ±12 V p-p
AC coupled
8 30 8 30 8 30 μV/°C
= ±5 V to ±16.5 V 50 150 50 150 μV/V
S
No load
±VS = +2.8 V/−3.2 V −1.6 −1.7 −1.6 −1.7 V
to Pin 1
DC 6.4 8 9.6 6.4 8 9.6 6.4 8 9.6 kΩ
VIN = 1 mV rms 1 1 1 kHz
= 10 mV rms 6 6 6 kHz
IN
= 100 mV rms 37 37 37 kHz
IN
= 200 mV rms 33 33 33 kHz
IN
±0.9
±4.0
−4 −5
−1.1 –0.9 V
±3
−4 −5
±0.9
±4.0
V
V
±3
V
V
±0.6
±3
mV
Rev. G | Page 4 of 24
AD737
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AD737A, AD737J AD737B, AD737K AD737J-5
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max Unit
3 dB
Bandwidth
V
V
V
Low-Z Input
(Pin 1)
1% Additional
Error
V
V
V
V
3 dB
Bandwidth
V
V
V
POWER-DOWN
MODE
Disable Voltage 0 0 V
Input Current,
PD Enabled
POWER SUPPLY
Operating
Voltage Range
Current No input 120
Rated input 170 210 170 210 170 210 μA
Powered down 25 40 25 40 25 40 μA
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 at 200 mV rms.
3
After fourth-order error correction using the equation
y = − 0.31009x4 − 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
/V rms.
PEAK
5
DC offset does not limit ac resolution.
VIN = 1 mV rms 5 5 5 kHz
= 10 mV rms 55 55 55 kHz
IN
= 100 mV rms 170 170 170 kHz
IN
= 200 mV rms 190 190 190 kHz
IN
VIN = 1 mV rms 1 1 1 kHz
= 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
VIN = 1 mV rms 5 5 5 kHz
= 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 = VS 11 11 μA
+2.8/−3.2 ±5 ±16.5 +2.8/−3.2 ±5 ±16.5 ±2.5 ±5 ±16.5 V
160
120
160
120
160
μA
Rev. G | Page 5 of 24
AD737
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ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
Supply Voltage ±16.5 V
Internal Power Dissipation 200 mW
Input Voltage ±VS
Output Short-Circuit Duration Indefinite
Differential Input Voltage +VS and −VS
Storage Temperature Range
CERDIP (Q-8) −65°C to +150°C
PDIP (N-8) and SOIC_N (R-8) −65°C to +125°C
Lead Temperature Range, Soldering (60 sec) 300°C
ESD Rating 500 V
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.
THERMAL RESISTANCE
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Table 3. Thermal Resistance
Package Type θJA Unit
8-Lead CERDIP (Q-8) 110 °C/W
8-Lead PDIP (N-8) 165 °C/W
8-Lead SOIC_N (R-8) 155 °C/W
ESD CAUTION
Rev. G | Page 6 of 24
AD737
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PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
C
V
POWER DOW N
–V
C
IN
S
1
AD737
2
3
TOP VIEW
(Not to Scale)
4
8
7
6
5
COM
+V
S
OUTPUT
C
AV
1
C
C
AD737
2
V
IN
TOP VIEW
–V
3
4
S
(Not to Scale)
POWER DOW N
00828-002
8
COM
+V
7
6
OUTPUT
5
C
1
C
S
AV
00828-003
POWER DOW N
V
–V
C
IN
S
2
AD737
TOP VIEW
3
(Not to Scale)
4
Figure 2. SOIC_N Pin Configuration (R-8) Figure 3. CERDIP Pin Configuration (Q-8) Figure 4. PDIP Pin Configuration (N-8)
Table 4. Pin Function Descriptions
Pin No. Mnemonic Description
1 CC Coupling Capacitor for Indirect DC Coupling.
2 VIN RMS Input.
3 POWER DOWN
4 –V
5 C
Negative Power Supply.
S
Averaging Capacitor.
AV
6 OUTPUT
7 +V
Positive Power Supply.
S
Disables the AD737. Low is enabled; high is powered down.
Output.
8 COM Common.
8
COM
7
+V
6
OUTPUT
5
C
S
AV
00828-004
Rev. G | Page 7 of 24
AD737
V
V
www.BDTIC.com/ADI
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, ±VS = ±5 V (except AD737J-5, ±VS = ±2.5 V), CAV = 33 µF, CC = 10 µF, f = 1 kHz, sine wave input applied to Pin 2, unless
otherwise specified.
0.7
0.5
VIN = 200mV rms
C
= 100µF
AV
C
= 22µF
F
10
CAV = 22µF, CF = 4.7µF, CC = 22µF
1V
0.3
0.1
0
–0.1
–0.3
ADDITIONA L ERROR (% of Read ing)
–0.5
04286121410 16
SUPPLY VOLTAGE (±V)
Figure 5. Additional Error vs. Supply Voltage
16
DC COUPL ED
14
12
10
8
6
4
PEAK INPUT BEFO RE CLIPPI NG (V)
2
0
04286121410 16
PIN 1
PIN 2
SUPPLY VOLTAGE (±V)
Figure 6. Maximum Input Level vs. Supply Voltage
25
20
100mV
10mV
INPUT LEVEL (rms)
1mV
00828-005
100µV
0.1 1 10010 1000
1% ERROR
10% ERROR
FREQUENCY (kHz)
–3dB
00828-008
Figure 8. Frequency Response Driving Pin 1
10
CAV = 22µF, CF = 4.7µF, CC = 22µF
1V
100mV
10mV
INPUT LEVEL (rms)
1mV
00828-006
100µV
0.1 1 10010 1000
1% ERROR
FREQUENCY (kHz )
10% ERROR
–3dB
00828-009
Figure 9. Frequency Response Driving Pin 2
6
3ms BURST OF 1kHz =
3 CYCLES
200mV rms SIGNA L
5
= 22µF
C
C
= 100µF
C
F
4
CAV = 10µF
CAV = 33µF
15
SUPPLY CURRENT (µA)
10
5
0246 81012141618
DUAL SUPPLY VOLTAGE (±V)
Figure 7. Supply Current (Power-Down Mode) vs. Supply Voltage (Dual)
00828-007
3
2
1
ADDITIONAL ERRO R (% of Readi ng)
0
12345
CREST FACTOR (V
Figure 10. Additional Error vs. Crest Factor
Rev. G | Page 8 of 24
CAV = 250µF
/V rms)
PEAK
CAV = 100µF
00828-010
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