ANALOG DEVICES AD736 Service Manual

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)
High input impedance: 10
Low input bias current: 25 pA maximum
High accuracy: ±0.3 mV ± 0.3% of reading
RMS conversion with signal crest factors up to 5
Wide power supply range: +2.8 V, −3.2 V to ±16.5 V
Low power: 200 mA maximum supply current
Buffered voltage output
No external trims needed for specified accuracy

AD737—an unbuffered voltage output version with

chip power-down also available

GENERAL DESCRIPTION

The AD736 is a low power, precision, monolithic true rms-to­dc converter. It is laser trimmed to provide a maximum error of
±0.3 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 size of
this converter make it suitable for upgrading the performance
of non-rms precision rectifiers in many applications. Compared
to these circuits, the AD736 offers higher accuracy at an equal
or lower cost.

The AD736 can compute the rms value of both ac and dc input
voltages. It can also be operated as an ac-coupled device by
adding one external capacitor. In this mode, the AD736 can
resolve input signal levels of 100 V 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 (introducing only 2.5%
additional error) at the 200 mV full-scale input level.

The AD736 has its own output buffer amplifier, thereby pro­viding a great deal of design flexibility. Requiring only 200 µA
of power supply current, the AD736 is optimized for use in
portable multimeters and other battery-powered applications.

12

Ω

True RMS-to-DC Converter

AD736

FUNCTIONAL BLOCK DIAGRAM

8k

1

C

C

FULL

WAVE

V

2

IN

AMPLIFI ER

C

3

F

–V

S

4

BIAS

SECTION

RECTIFIER

INPUT

rms CORE

Figure 1.

AD736

8k

OUTPUT

AMPLIFI ER

The AD736 allows the choice of two signal input terminals: a

12

high impedance FET input (10

Ω) that directly interfaces with
High-Z input attenuators and a low impedance input (8 kΩ) that
allows the measurement of 300 mV input levels while operating
from the minimum power supply voltage of +2.8 V, −3.2 V. The
two inputs can be used either single ended or differentially.

The AD736 has a 1% reading error bandwidth that exceeds
10 kHz for the input amplitudes from 20 mV rms to 200 mV rms
while consuming only 1 mW.

The AD736 is available in four performance grades. The
AD736J and AD736K grades are rated over the 0°C to +70°C
and −20°C to +85°C commercial temperature ranges. The
AD736A and AD736B grades are rated over the −40°C to +85°C
industrial temperature range. The AD736 is available in three
low cost, 8-lead packages: PDIP, SOIC, and CERDIP.

PRODUCT HIGHLIGHTS

1. The AD736 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 AD736 to perform true rms measurement.

3. The low power consumption of 1 mW makes the AD736

suitable for many battery-powered applications.

12

4. A high input impedance of 10

external buffer when interfacing with input attenuators.

5. A low impedance input is available for those applications that

require an input signal up to 300 mV rms operating from low
power supply voltages.

Ω eliminates the need for an

8

COM

+V

7

6

OUTPUT

C

5

S

AV

00834-001

Rev. H

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: [phone] www.analog.com
Fax: [phone] ©2007 Analog Devices, Inc. All rights reserved.

AD736

TABLE OF CONTENTS

Features .............................................................................................. 1

General Description......................................................................... 1

Functional Block Diagram .............................................................. 1

Product Highlights........................................................................... 1

Revision History ............................................................................... 2

Specifications..................................................................................... 3

Absolute Maximum Ratings............................................................ 5

ESD Caution.................................................................................. 5

Pin Configuration and Function Descriptions............................. 6

Typical Performance Characteristics ............................................. 7

Theory of Operation ...................................................................... 10

Types of AC Measu r e m e nt ........................................................ 10

Calculating Settling Time Using Figure 16 ............................. 11

REVISION HISTORY

2/07—Rev. G to Rev. H

Updated Layout.......................................................................9 to 12

Added Applications Section......................................................... 13

Inserted Figure 21 to Figure 24; Renumbered Sequentially..... 13

Deleted Figure 25........................................................................... 15

Added Evaluation Board Section ................................................ 16

Inserted Figure 29 to Figure 34; Renumbered Sequentially..... 16

Inserted Figure 35; Renumbered Sequentially........................... 17

Added Table 6................................................................................. 17

2/06—Rev. F to Rev. G

Updated Format.................................................................Universal

Changes to Features......................................................................... 1

Added Table 3................................................................................... 6

Changes to Figure 21 and Figure 22............................................ 14

Changes to Figure 23, Figure 24, and Figure 25 ........................ 15

Updated Outline Dimensions...................................................... 16

Changes to Ordering Guide......................................................... 17

5/04—Rev. E to Rev. F

Changes to Specifications............................................................... 2

Replaced Figure 18 ........................................................................10

Updated Outline Dimensions...................................................... 16

Changes to Ordering Guide......................................................... 16

RMS Measurement—Choosing the Optimum Value for C

....................................................................................................... 11

Rapid Settling Times via the Average Responding

Connection.................................................................................. 12

DC Error, Output Ripple, and Averaging Error..................... 12

AC Measurement Accuracy and Crest Factor............................ 12

Applications..................................................................................... 13

Connecting the Input................................................................. 13

Selecting Practical Values for Input Coupling (CC), Averaging
(C

), and Filtering (C

AV

Evaluation Board ............................................................................ 16

Outline Dimensions ....................................................................... 18

Ordering Guide .......................................................................... 19

4/03—Rev. D to Rev. E

Changes to General Description .................................................1

Changes to Specifications.............................................................3

Changes to Absolute Maximum Ratings....................................4

Changes to Ordering Guide.........................................................4

11/02—Rev. C to Rev. D

Changes to Functional Block Diagram.......................................1

Changes to Pin Configuration.....................................................3

Figure 1 Replaced ..........................................................................6

Changes to Figure 2.......................................................................6

Changes to Application Circuits Figures 4 to 8.........................8

Outline Dimensions Updated......................................................8

) Capacitors......................................... 14

F

AV

Rev. H | Page 2 of 20

AD736

SPECIFICATIONS

At 25°C ± 5 V supplies, ac-coupled with 1 kHz sine wave input applied, unless otherwise noted. Specifications in bold are tested on all
production units at final electrical test. Results from those tests are used to calculate outgoing quality levels.

Table 1.

AD736J/AD736A AD736K/AD736B
Parameter Conditions Min Typ Max Min Typ Max Unit

TRANSFER FUNCTION V

= √Avg (V

OUT

CONVERSION ACCURACY 1 kHz sine wave

Total Error, Internal Trim

All Grades 0 mV rms to 200 mV rms 0.3/0.3

200 mV to 1 V rms −1.2

T

to T

MIN

MAX

A and B Grades @ 200 mV rms
J and K Grades @ 200 mV rms 0.007

vs. Supply Voltage

@ 200 mV rms Input VS = ±5 V to ±16.5 V

V

DC Reversal Error, DC-Coupled @ 600 mV dc
Nonlinearity2, 0 mV to 200 mV @ 100 mV rms

1

Using C

C

0.5/0.5
±2.0

0.7/0.7

+0.06

−0.18

+0.1 0

−0.3 0

1.3 2.5

0.25

0.35 0

= ±5 V to ±3 V

S

0
0

0

Total Error, External Trim 0 mV rms to 200 mV rms 0.1/0.5 0.1/0.3 ±mV/±% of reading

ERROR VS. CREST FACTOR

3

Crest Factor = 1 to 3 CAV, CF = 100 μF 0.7 0.7 % additional error
Crest Factor = 5 CAV, CF = 100 μF 2.5 2.5 % additional error

INPUT CHARACTERISTICS

High Impedance Input

Signal Range (Pin 2)

Continuous RMS Level VS = +2.8 V, −3.2 V

V

Peak Transient Input VS = +2.8 V, −3.2 V
V
V

= ±5 V to ±16.5 V

S

±0.9

= ±5 V

S

= ±16.5 V

S

±4.0

Input Resistance 10

±2.7

12

200
1

10

Input Bias Current VS = ±3 V to ±16.5 V 1 25 1 25 pA

Low Impedance Input

Signal Range (Pin 1)

Continuous RMS Level VS = +2.8 V, –3.2 V 300 300 mV rms
V

= ±5 V to ±16.5 V 1 1 V rms

S

Peak Transient Input VS = +2.8 V, −3.2 V ±1.7 ±1.7 V
V
V

= ±5 V ±3.8 ±3.8 V

S

= ±16.5 V ±11 ±11 V

S

Input Resistance 6.4 8 9.6 6.4 8 9.6 kΩ

Maximum Continuous

All supply voltages ±12 ±12 V p-p

Nondestructive Input

Input Offset Voltage

J and K Grades

A and B Grades

4

±3
±3

vs. Temperature 8 30 8 30 μV/°C

vs. Supply VS = ±5 V to ±16.5 V 50
V

= ±5 V to ±3 V 80 80 μV/V

S

150

2

)

IN

0.2/0.2

−1.2

0.007

+0.06

−0.18

1.3 2.5 % of reading

0.25

±0.9

±4.0

V
±2.7 V
V

50

0.3/0.3
±2.0

0.5/0.5

+0.1

−0.3

0.35

200
1

12

Ω

±3
±3

150

±mV/±% of reading
% of reading

±mV/±% of reading
±% of reading/°C

%/V
%/V

% of reading

mV rms
V rms

mV
mV

μV/V

Rev. H | Page 3 of 20

AD736

AD736J/AD736A AD736K/AD736B
Parameter Conditions Min Typ Max Min Typ Max Unit

OUTPUT CHARACTERISTICS

Output Offset Voltage

J and K Grades ±0.1
A and B Grades

±0.5
±0.5

vs. Temperature 1 20 1 20 μV/°C
vs. Supply VS = ±5 V to ±16.5 V 50

V

= ±5 V to ±3 V 50 50 μV/V

S

130

Output Voltage Swing

2 kΩ Load VS = +2.8 V, −3.2 V

0 to

1.7

1.6

V

= ±5 V

S

0 to

3.8

3.6

V

No Load VS = ±16.5 V

= ±16.5 V

S

0 to 4
0 to 4

5

12
Output Current 2 2 mA
Short-Circuit Current 3 3 mA
Output Resistance @ dc 0.2 0.2 Ω

FREQUENCY RESPONSE

High Impedance Input (Pin 2)

Sine wave input

for 1% Additional Error

VIN = 1 mV rms 1 1 kHz
VIN = 10 mV rms 6 6 kHz
VIN = 100 mV rms 37 37 kHz
VIN = 200 mV rms 33 33 kHz

±3 dB Bandwidth Sine wave input

VIN = 1 mV rms 5 5 kHz
VIN = 10 mV rms 55 55 kHz
VIN = 100 mV rms 170 170 kHz
VIN = 200 mV rms 190 190 kHz

Low Impedance Input (Pin 1)

Sine wave input

for 1% Additional Error

VIN = 1 mV rms 1 1 kHz
VIN = 10 mV rms 6 6 kHz
VIN = 100 mV rms 90 90 kHz
VIN = 200 mV rms 90 90 kHz

±3 dB Bandwidth Sine wave input

VIN = 1 mV rms 5 5 kHz
VIN = 10 mV rms 55 55 kHz
VIN = 100 mV rms 350 350 kHz
VIN = 200 mV rms 460 460 kHz

POWER SUPPLY

Operating Voltage Range +2.8, −3.2 ± 5 ±16.5 +2.8, −3.2 ± 5 ±16.5 V
Quiescent Current Zero signal 160

200

200 mV rms, No Load Sine wave input 230 270 230 270 μA

TEMPERATURE RANGE

Operating, Rated Performance

Commercial 0°C to 70°C AD736JN, AD736JR AD736KN, AD736KR
Industrial −40°C to +85°C AD736AQ, AD736AR AD736BQ, AD736BR

1

Accuracy is specified with the AD736 connected as shown in Figure 18 with Capacitor CC.

2

Nonlinearity is defined as the maximum deviation (in percent error) from a straight line conn ecting the readings at 0 mV rms and 200 mV rms. Output offset voltage is adjusted to zero.

3

Error vs. crest factor is specified as additional error for a 200 mV rms signal. Crest factor = V

4

DC offset does not limit ac resolution.

PEAK

/V rms.

±0.1

50

0 to

1.7 V

±0.3
±0.3

130

1.6
0 to

3.8 V

3.6

0 to 4
0 to 4

160

5 V
12 V

200

mV
mV

μV/V

μA

Rev. H | Page 4 of 20

AD736

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter Rating

Supply Voltage ±16.5 V
Internal Power Dissipation
Input Voltage ±V
Output Short-Circuit Duration Indefinite
Differential Input Voltage +VS and –V
Storage Temperature Range (Q) –65°C to +150°C
Storage Temperature Range (N, R) –65°C to +125°C
Lead Temperature (Soldering, 60 sec) 300°C
ESD Rating 500 V

1

8-Lead PDIP: θJA = 165°C/W, 8-Lead CERDIP: θJA = 110°C/W, and

8-Lead SOIC: θJA = 155°C/W.

1

200 mW

S

S

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.

ESD CAUTION

Rev. H | Page 5 of 20

AD736

–V

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

Table 3. Pin Function Descriptions

Pin No. Mnemonic Description

1 C

C

Coupling Capacitor. If dc coupling is desired at Pin 2, connect a coupling capacitor to this pin. If the coupling at
Pin 2 is ac, connect this pin to ground. Note that this pin is also an input, with an input impedance of 8 kΩ.

Such an input is useful for applications with high input voltages and low supply voltages.
2 V
3 C
4 −V
5 C

IN

F

S

AV

High Input Impedance Pin.

Connect an Auxiliary Low-Pass Filter Capacitor from the Output.

Negative Supply Voltage if Dual Supplies Are Used, or Ground if Connected to a Single-Supply Source.

Connect the Averaging Capacitor Here.
6 OUTPUT DC Output Voltage.
7 +V

S

Positive Supply Voltage.
8 COM Common.

1

C

C

AD736

2

V

IN

TOP VIEW

C

3

(Not to Scale)

F

4

S

Figure 2. Pin Configuration

8

COM

7

+V

OUTPUT

6

C

5

S

AV

00834-025

Rev. H | Page 6 of 20