Analog Devices AD637 Datasheet

High Precision,

BUFFER

AD637

ABSOLUTE

VALUE

SQUARER/DIVIDER

BIAS

SECTION

FILTER

25kV

25kV

1

2

3

4

5

6

7

14

13

12

11

10

98

16

15

SOIC (R) Package

BUFFER

AD637

ABSOLUTE

VALUE

SQUARER/DIVIDER

BIAS

SECTION

FILTER

25kV

25kV

1

2

3

4

5

6

7

14

13

12

11

10

9

8

Ceramic DIP (D) and

Cerdip (Q) Packages

a

FEATURES
High Accuracy

0.02% Max Nonlinearity, 0 V to 2 V RMS Input

0.10% Additional Error to Crest Factor of 3

Wide Bandwidth

8 MHz at 2 V RMS Input
600 kHz at 100 mV RMS

Computes:

True RMS
Square
Mean Square

Absolute Value
dB Output (60 dB Range)
Chip Select-Power Down Feature Allows:

Analog “3-State” Operation

Quiescent Current Reduction from 2.2 mA to 350 ␮A
Side-Brazed DIP, Low Cost Cerdip and SOIC

PRODUCT DESCRIPTION

The AD637 is a complete high accuracy monolithic rms-to-dc
converter that computes the true rms value of any complex
waveform. It offers performance that is unprecedented in inte­grated circuit rms-to-dc converters and comparable to discrete
and modular techniques in accuracy, bandwidth and dynamic
range. A crest factor compensation scheme in the AD637 per­mits measurements of signals with crest factors of up to 10 with
less than 1% additional error. The circuit’s wide bandwidth per­mits the measurement of signals up to 600 kHz with inputs of
200 mV rms and up to 8 MHz when the input levels are above
1 V rms.

As with previous monolithic rms converters from Analog Devices,
the AD637 has an auxiliary dB output available to the user. The
logarithm of the rms output signal is brought out to a separate
pin allowing direct dB measurement with a useful range of
60 dB. An externally programmed reference current allows the
user to select the 0 dB reference voltage to correspond to any
level between 0.1 V and 2.0 V rms.

A chip select connection on the AD637 permits the user to

decrease the supply current from 2.2 mA to 350 µA during

periods when the rms function is not in use. This feature facili­tates the addition of precision rms measurement to remote or
hand-held applications where minimum power consumption is
critical. In addition when the AD637 is powered down the out­put goes to a high impedance state. This allows several AD637s
to be tied together to form a wide-band true rms multiplexer.

The input circuitry of the AD637 is protected from overload
voltages that are in excess of the supply levels. The inputs will
not be damaged by input signals if the supply voltages are lost.

REV. E

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.

Wide-Band RMS-to-DC Converter

AD637

FUNCTIONAL BLOCK DIAGRAMS

The AD637 is available in two accuracy grades (J, K) for com-

mercial (0°C to +70°C) temperature range applications; two
accuracy grades (A, B) for industrial (–40°C to +85°C) applica­tions; and one (S) rated over the –55°C to +125°C temperature

range. All versions are available in hermetically-sealed, 14-lead
side-brazed ceramic DIPs as well as low cost cerdip packages. A
16-lead SOIC package is also available.

PRODUCT HIGHLIGHTS

1. The AD637 computes the true root-mean-square, mean
square, or absolute value of any complex ac (or ac plus dc)
input waveform and gives an equivalent dc output voltage.
The true rms value of a waveform is more useful than an
average rectified signal since it relates directly to the power of
the signal. The rms value of a statistical signal is also related
to the standard deviation of the signal.

2. The AD637 is laser wafer trimmed to achieve rated perfor­mance without external trimming. The only external compo­nent required is a capacitor which sets the averaging time
period. The value of this capacitor also determines low fre­quency accuracy, ripple level and settling time.

3. The chip select feature of the AD637 permits the user to
power down the device down during periods of nonuse,
thereby, decreasing battery drain in remote or hand-held
applications.

4. The on-chip buffer amplifier can be used as either an input
buffer or in an active filter configuration. The filter can be
used to reduce the amount of ac ripple, thereby, increasing
the accuracy of the measurement.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] World Wide Web Site: http://www.analog.com
Fax: [phone] © Analog Devices, Inc., 1999

AD637–SPECIFICATIONS

Model Min Typ Max Min Typ Max Min Typ Max Units

TRANSFER FUNCTION

CONVERSION ACCURACY

Total Error, Internal Trim

T

to T

MIN

MAX

vs. Supply, + V
vs. Supply, – V

DC Reversal Error at 2 V 0.25 0.1 0.25 % of Reading
Nonlinearity 2 V Full Scale
Nonlinearity 7 V Full Scale 0.05 0.05 0.05 % of FSR
Total Error, External Trim ±0.5 ± 0.1 ±0.25 ± 0.05 ±0.5 ± 0.1 mV ± % of Reading

ERROR VS. CREST FACTOR

Crest Factor 1 to 2 Specified Accuracy Specified Accuracy Specified Accuracy
Crest Factor = 3 ±0.1 ± 0.1 ±0.1 % of Reading

1

(Fig. 2) ⴞ1 ⴞ 0.5 ⴞ0.5 ⴞ 0.2 ⴞ1 ⴞ 0.5 mV ± % of Reading

= +300 mV 30 150 30 150 30 150 µV/V

IN

= –300 mV 100 300 100 300 100 300 µV/V

IN

2

3

AD637J/A AD637K/B AD637S

V

= avg .(V

OUT

(@ +25ⴗC, and ⴞ15 V dc unless otherwise noted)

2

)

IN

V

OUT

= avg .(V

ⴞ3.0 ⴞ 0.6 ⴞ2.0 ⴞ 0.3 ⴞ 6 ⴞ 0.7 mV ± % of Reading

0.04 0.02 0.04 % of FSR

2

)

IN

V

= avg .(V

OUT

2

)

IN

Crest Factor = 10 ±1.0 ±1.0 ±1.0 % of Reading

AVERAGING TIME CONSTANT 25 25 25 ms/µF C

INPUT CHARACTERISTICS

Signal Range, ±15 V Supply

Continuous RMS Level 0 to 7 0 to 7 0 to 7 V rms

Peak Transient Input ±15 ± 15 ±15 V p-p
Signal Range, ±5 V Supply

Continuous rms Level 0 to 4 0 to 4 0 to 4 V rms

Peak Transient Input ±6 ±6 ±6 V p-p
Maximum Continuous Nondestructive

Input Level (All Supply Voltages) ±15 ± 15 ±15 V p-p
Input Resistance 6.4 8 9.6 6.4 8 9.6 6.4 8 9.6 kΩ
Input Offset Voltage ±0.5 ±0.2 ±0.5 mV

FREQUENCY RESPONSE

Bandwidth for 1% Additional Error (0.09 dB)

V

= 20 mV 11 11 11 kHz

IN

V

= 200 mV 66 66 66 kHz

IN

V

= 2 V 200 200 200 kHz

IN

±3 dB Bandwidth

V

= 20 mV 150 150 150 kHz

IN

V

= 200 mV 1 1 1 MHz

IN

VIN = 2 V 8 8 8 MHz

OUTPUT CHARACTERISTICS

Offset Voltage ⴞ1 ⴞ0.5 ⴞ1 mV

vs. Temperature ±0.05 ⴞ0.089 ± 0.04 ⴞ0.056 ± 0.04 ⴞ0.07 mV/°C
Voltage Swing, ±15 V Supply,

2 kΩ Load 0 to +12.0 +13.5 0 to +12.0 +13.5 0 to +12.0 +13.5 V
Voltage Swing, ±3 V Supply,

2 kΩ Load 0 to +2 +2.2 0 to +2 +2.2 0 to +2 +2.2 V
Output Current 66 6mA
Short Circuit Current 20 20 20 mA
Resistance, Chip Select “High” 0.5 0.5 0.5 Ω

4

AV

Resistance, Chip Select “Low” 100 100 100 kΩ

dB OUTPUT

BUFFER AMPLIFIER

DENOMINATOR INPUT

CHIP SELECT PROVISION (CS)

POWER SUPPLY

7 mV to 7 V rms, 0 dB = 1 V rms ±0.5 ± 0.3 ±0.5 dB

Error, V

IN

Scale Factor –3 –3 –3 mV/dB
Scale Factor Temperature Coefficient +0.33 +0.33 +0.33 % of Reading/°C

I

for 0 dB = 1 V rms 5 20 80 52080 52080 µA

REF

I

Range 1 100 1 100 1 100 µA

REF

Input Output Voltage Range –V
Input Offset Voltage ±0.8 ⴞ 2 ±0.5 ⴞ1 ±0.8 ⴞ2 mV

Input Current ±2 ⴞ 10 ±2 ⴞ5 ±2 ⴞ10 nA
Input Resistance 10
Output Current (+5 mA, (+5 mA, (+5 mA,

Short Circuit Current 20 20 20 mA
Small Signal Bandwidth 1 1 1 MHz

5

Slew Rate

Input Range 0 to +10 0 to +10 0 to +10 V
Input Resistance 20 25 30 20 25 30 20 25 30 k Ω
Offset Voltage ±0.2 ±0.5 ±0.2 ± 0.5 ±0.2 ±0.5 mV

RMS “ON” Level Open or +2.4 V < V
RMS “OFF” Level VC < +0.2 V VC < +0.2 V VC < +0.2 V
I

of Chip Select

OUT

CS “LOW” 10 10 10 µA

CS “HIGH” Zero Zero Zero
On Time Constant 10 µs + ((25 kΩ) × C
Off Time Constant 10 µs + ((25 kΩ) × CAV) 10 µs + ((25 kΩ) × CAV) 10 µs + ((25 kΩ) × C

Operating Voltage Range ⴞ3.0 ⴞ18 ⴞ3.0 ⴞ18 ⴞ3.0 ⴞ18 V
Quiescent Current 2.2 3 2.2 3 2.2 3 mA
Standby Current 350 450 350 450 350 450 µA

– 2.5 V) – 2.5 V) – 2.5 V) V

–130 µA) –130 µA) –130 µA)

–0.033 –0.033 –0.033 dB/°C

to (+V

S

S

8

–VS to (+V

S

8

10

–VS to (+V

S

8

10

55 5V/µs

< +V

C

S

) 10 µs + ((25 kΩ) × CAV) 10 µs + ((25 kΩ) × C

AV

Open or +2.4 V < VC < +V

S

Open or +2.4 V < VC < +V

Ω

S

)

AV

)

AV

TRANSISTOR COUNT 107 107 107

–2–

REV. E

AD637

WARNING!

ESD SENSITIVE DEVICE

NOTES

1

Accuracy specified 0-7 V rms dc with AD637 connected as shown in Figure 2.

2

Nonlinearity is defined as the maximum deviation from the straight line connecting the readings at 10 mV and 2 V.

3

Error vs. crest factor is specified as additional error for 1 V rms.

4

Input voltages are expressed in volts rms. % are in % of reading.

5

With external 2 kΩ pull down resistor tied to –V

Specifications subject to change without notice.

Specifications shown in boldface are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. All min
and max specifications are guaranteed, although only those shown in boldface are tested on all production units.

.

S

ABSOLUTE MAXIMUM RATINGS

ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 V

Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±18 V dc

Internal Quiescent Power Dissipation . . . . . . . . . . . . 108 mW

Output Short-Circuit Duration . . . . . . . . . . . . . . . . . Indefinite

Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C

Lead Temperature Range (Soldering 10 secs) . . . . . . . +300°C

Rated Operating Temperature Range

AD637J, K . . . . . . . . . . . . . . . . . . . . . . . . . . . 0°C to +70°C

AD637A, B . . . . . . . . . . . . . . . . . . . . . . . . –40°C to +85°C

AD637S, 5962-8963701CA . . . . . . . . . . . –55°C to +125°C

BUFF OUT

BUFF IN

A5

BUFFER

AMPLIFIER

ORDERING GUIDE

Temperature Package Package

Model Range Description Option

AD637AR – 40°C to +85°C SOIC R-16
AD637BR –40°C to +85°C SOIC R-16
AD637AQ – 40°C to +85°C Cerdip Q-14
AD637BQ –40°C to +85°C Cerdip Q-14
AD637JD 0°C to +70°C Side Brazed Ceramic DIP D-14
AD637JD/+ 0°C to +70°C Side Brazed Ceramic DIP D-14
AD637KD 0°C to +70°C Side Brazed Ceramic DIP D-14
AD637KD/+ 0°C to +70°C Side Brazed Ceramic DIP D-14
AD637JQ 0°C to +70°C Cerdip Q-14
AD637KQ 0°C to +70°C Cerdip Q-14
AD637JR 0°C to +70°C SOIC R-16
AD637JR-REEL 0°C to +70°C SOIC R-16
AD637JR-REEL7 0°C to +70°C SOIC R-16
AD637KR 0°C to +70°C SOIC R-16
AD637SD –55°C to +125°C Side Brazed Ceramic DIP D-14
AD637SD/883B –55°C to +125°C Side Brazed Ceramic DIP D-14
AD637SQ/883B –55°C to +125°C Cerdip Q-14
AD637SCHIPS 0°C to +70°CDie
5962-8963701CA* –55°C to +125°C Cerdip Q-14

*A standard microcircuit drawing is available.

ONE QUADRANT

SQUARER/DIVIDER

I

4

FILTER/AMPLIFIER

24kV

A4

CAV

+V
RMS

OUT

S

I

6kV

1

Q3

Q4

Q5

I

A3

125V

3

Q1

Q2

A2

24kV

ABSOLUTE VALUE VOLTAGE –

CURRENT CONVERTER

6kV

V

12kV

IN

A1

Figure 1. Simplified Schematic

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 the AD637 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.

REV. E –3–

BIAS

24kV

AD637

dB

OUT
COM

CS
DEN

INPUT
OUTPUT

OFFSET

–V

S