Analog Devices AD637SQ-883B, AD637SD-883B, AD637SD, AD637SCHIPS, AD637KR Datasheet

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5 (1)

a

High Precision, Wideband

RMS-to-DC Converter

 

 

AD637

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 “Three-State” Operation

Quiescent Current Reduction from 2.2 mA to 350 A

Side Brazed DIP, Low Cost Cerdip and SOIC

FUNCTIONAL BLOCK DIAGRAMS

Ceramic DIP (D) and

SOIC (R) Package

Cerdip (Q) Packages

 

 

 

 

 

 

 

 

 

 

 

BUFFER

AD637

 

 

BUFFER

AD637

 

1

 

14

1

 

 

16

2

ABSOLUTE

13

2

 

ABSOLUTE

15

 

VALUE

 

 

 

VALUE

 

3

 

12

3

BIAS

 

14

BIAS

 

 

 

 

 

SECTION

SQUARER/DIVIDER

 

4

SECTION

SQUARER/DIVIDER

13

4

11

 

 

 

 

 

25k

 

5

 

25k

12

5

 

10

 

 

25k

 

9

6

25k

 

11

6

 

 

 

7

FILTER

8

7

 

FILTER

10

 

 

 

8

 

 

9

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 A 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 wideband 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. 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. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

The AD637 is available in two accuracy grades (J and K) for commercial (0°C to 70°C) temperature range applications; two accuracy grades (A and 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, meansquare, 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 that 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 during periods of nonuse, thereby decreasing battery drain in remote or hand-held applications.

4.The on-chip buffer amplifier can be used either as 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: 781/329-4700

www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 2002

AD637–SPECIFICATIONS (@ 25 C, and 15 V dc unless otherwise noted.)

 

 

AD637J/A

 

 

AD637K/B

 

AD637S

 

 

Model

Min

Typ

Max

Min

Typ

Max

Min

Typ

Max

Unit

 

 

 

 

 

 

 

 

TRANSFER FUNCTION

 

VOUT = avg × (VIN )2

 

VOUT = avg × (VIN )2

VOUT =

avg × (VIN )2

 

CONVERSION ACCURACY

 

 

 

 

 

 

 

 

 

mV ± % of Reading

Total Error, Internal Trim1 (Fig. 2)

 

 

1 0.5

 

 

0.5 0.2

 

 

1 0.5

TMIN to TMAX

 

 

3.0 0.6

 

 

2.0 0.3

 

 

6 0.7

mV ± % of Reading

vs. Supply, + VIN = +300 mV

 

30

150

 

30

150

 

30

150

µV/V

vs. Supply, – VIN = –300 mV

 

100

300

 

100

300

 

100

300

µV/V

DC Reversal Error at 2 V

 

 

0.25

 

 

0.1

 

 

0.25

% of Reading

Nonlinearity 2 V Full Scale2

 

 

0.04

 

 

0.02

 

 

0.04

% of FSR

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 FACTOR3

 

 

 

 

 

 

 

 

 

 

Crest Factor 1 to 2

Specified Accuracy

 

Specified Accuracy

 

Specified Accuracy

 

Crest Factor = 3

 

± 0.1

 

 

± 0.1

 

 

± 0.1

 

% of Reading

Crest Factor = 10

 

± 1.0

 

 

± 1.0

 

 

± 1.0

 

% of Reading

AVERAGING TIME CONSTANT

 

25

 

 

25

 

 

25

 

ms/µF CAV

INPUT CHARACTERISTICS

 

 

 

 

 

 

 

 

 

 

Signal Range, ± 15 V Supply

 

 

 

 

 

 

 

 

 

 

Continuous RMS Level

 

0 to 7

± 15

 

0 to 7

± 15

 

0 to 7

± 15

V rms

Peak Transient Input

 

 

 

 

 

 

V p-p

Signal Range, ± 5 V Supply

 

 

 

 

 

 

 

 

 

 

Continuous rms Level

 

0 to 4

± 6

 

0 to 4

± 6

 

0 to 4

± 6

V rms

Peak Transient Input

 

 

 

 

 

 

V p-p

Maximum Continuous Nondestructive

 

 

± 15

 

 

± 15

 

 

± 15

 

Input Level (All Supply Voltages)

 

 

 

 

 

 

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 RESPONSE4

 

 

 

 

 

 

 

 

 

 

Bandwidth for 1% Additional Error (0.09 dB)

 

 

 

 

 

 

 

 

 

VIN = 20 mV

 

11

 

 

11

 

 

11

 

kHz

VIN = 200 mV

 

66

 

 

66

 

 

66

 

kHz

VIN = 2 V

 

200

 

 

200

 

 

200

 

kHz

± 3 dB Bandwidth

 

 

 

 

 

 

 

 

 

 

VIN = 20 mV

 

150

 

 

150

 

 

150

 

kHz

VIN = 200 mV

 

1

 

 

1

 

 

1

 

MHz

VIN = 2 V

 

8

 

 

8

 

 

8

 

MHz

OUTPUT CHARACTERISTICS

 

 

1

 

 

0.5

 

 

1

mV

Offset Voltage

 

 

 

 

 

 

vs. Temperature

 

± 0.05

0.089

 

± 0.04

0.056

 

± 0.04

0.07

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

6

 

 

6

 

 

6

 

 

mA

Short Circuit Current

 

20

 

 

20

 

 

20

 

mA

Resistance, Chip Select “High”

 

0.5

 

 

0.5

 

 

0.5

 

Resistance, Chip Select “Low”

 

100

 

 

100

 

 

100

 

kΩ

dB OUTPUT

 

± 0.5

 

 

± 0.3

 

 

± 0.5

 

 

Error, VIN 7 mV to 7 V rms,

 

 

 

 

 

 

dB

0 dB = 1 V rms

 

 

 

 

 

 

 

 

 

 

Scale Factor

 

–3

 

 

–3

 

 

–3

 

mV/dB

Scale Factor Temperature Coefficient

 

+0.33

 

 

+0.33

 

 

+0.33

 

% of Reading/°C

 

 

–0.033

 

 

–0.033

 

 

–0.033

 

dB/°C

IREF for 0 dB = 1 V rms

5

20

80

5

20

80

5

20

80

µA

IREF Range

1

 

100

1

 

100

1

 

100

µA

BUFFER AMPLIFIER

–VS to (+VS – 2.5 V)

 

–VS to (+VS – 2.5 V)

 

–VS to (+VS – 2.5 V)

 

V

Input Output Voltage Range

 

 

 

Input Offset Voltage

 

± 0.8

2

 

± 0.5

1

 

± 0.8

2

mV

Input Current

 

± 2

10

 

± 2

5

 

± 2

10

nA

Input Resistance

 

108

 

 

108

 

 

108

 

Output Current

(+5 mA, –130 µA)

 

(+5 mA, –130 µA)

 

(+5 mA, –130 µA)

 

 

Short Circuit Current

 

20

 

 

20

 

 

20

 

mA

Small Signal Bandwidth

 

1

 

 

1

 

 

1

 

MHz

Slew Rate5

 

5

 

 

5

 

 

5

 

V/µs

DENOMINATOR INPUT

 

 

 

 

 

 

 

 

 

 

Input Range

 

0 to 10

 

 

0 to 10

 

 

0 to 10

 

V

Input Resistance

20

25

30

20

25

30

20

25

30

kΩ

Offset Voltage

 

± 0.2

± 0.5

 

± 0.2

± 0.5

 

± 0.2

± 0.5

mV

–2–

REV. F

 

 

 

 

 

 

 

 

 

 

AD637

 

 

 

 

 

 

 

 

 

 

 

 

 

 

AD637J/A

 

AD637K/B

 

AD637S

 

 

 

 

 

Model

Min

Typ

Max

Min

Typ

Max

Min

Typ

Max

 

Unit

 

 

 

 

 

 

 

 

 

 

 

 

CHIP SELECT PROVISION (CS)

 

 

 

 

 

 

 

 

 

 

 

RMS “ON” Level

Open or 2.4 V < VC < +VS

Open or 2.4 V < VC < +VS

Open or 2.4 V < VC < +VS

 

 

RMS “OFF” Level

VC < 0.2 V

 

VC < 0.2 V

 

VC < 0.2 V

 

 

 

 

 

 

IOUT of Chip Select

 

 

 

 

 

 

 

 

 

 

 

CS “Low”

10

 

 

10

 

 

10

 

 

 

µA

CS “High”

Zero

 

 

Zero

 

 

Zero

 

 

 

 

On Time Constant

10 µs + ((25 kΩ) CAV)

 

10 µs + ((25 kΩ) CAV)

 

10 µs + ((25 kΩ) CAV)

 

 

 

Off Time Constant

10 µs + ((25 kΩ) CAV)

 

10 µs + ((25 kΩ) CAV)

 

10 µs + ((25 kΩ) CAV)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

POWER SUPPLY

 

 

 

 

 

 

 

 

 

 

 

Operating Voltage Range

± 3.0

 

18

3.0

 

18

3.0

 

18

 

V

Quiescent Current

 

2.2

3

 

2.2

3

 

2.2

3

 

mA

Standby Current

 

350

450

 

350

450

 

350

450

 

µA

 

 

 

 

 

 

 

 

 

 

 

 

TRANSISTOR COUNT

 

107

 

 

107

 

 

107

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NOTES

1Accuracy specified 0–7 V rms dc with AD637 connected as shown in Figure 2.

2Nonlinearity is defined as the maximum deviation from the straight line connecting the readings at 10 mV and 2 V. 3Error vs. crest factor is specified as additional error for 1 V rms.

4Input voltages are expressed in volts rms. % are in % of reading. 5With external 2 kΩ pull-down resistor tied to –VS.

Specifications shown in bold 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.

Specifications subject to change without notice.

REV. F

–3–

Analog Devices AD637SQ-883B, AD637SD-883B, AD637SD, AD637SCHIPS, AD637KR Datasheet

AD637

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

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

–55°C to +125°C

Die

 

5962-8963701CA*

–55°C to +125°C

Cerdip

Q-14

 

 

 

 

*A standard microcircuit drawing is available.

 

 

 

 

 

FILTER/AMPLIFIER

CAV

BUFF OUT

 

ONE QUADRANT

 

24k

 

 

 

BUFF IN

 

SQUARER/DIVIDER

 

 

 

+VS

 

BUFFER

 

 

 

 

A5

 

AMPLIFIER

 

 

A4

 

RMS

 

 

 

 

I4

 

 

 

 

 

 

OUT

 

 

I1

 

 

 

 

dB

24k

 

 

 

 

 

OUT

 

 

 

 

 

 

 

 

 

 

Q4

 

 

 

COM

 

 

 

 

 

 

 

ABSOLUTE VALUE VOLTAGE –

Q1

 

 

Q5

BIAS

CS

 

 

 

CURRENT CONVERTER

 

 

 

 

 

DEN

 

 

 

 

 

 

 

6k

6k

Q2

Q3

A3

I3

24k

INPUT

OUTPUT

 

 

 

 

 

 

 

 

 

A2

 

 

 

 

OFFSET

 

 

 

 

 

 

 

12k

 

 

 

 

125

AD637

 

VIN

 

 

 

 

 

 

A1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

–VS

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.

WARNING!

ESD SENSITIVE DEVICE

–4–

REV. F

 

 

 

 

 

 

 

 

 

 

 

 

 

AD637

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PIN CONFIGURATIONS

 

 

 

 

 

14-Lead DIP

 

 

 

16-Lead SOIC

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BUFF IN

1

 

 

 

14

BUFF OUT

BUFF IN

1

 

16

BUFF OUT

 

 

 

 

 

 

 

V

 

 

 

 

 

 

 

V

 

NC

2

 

15

 

NC

2

 

 

 

13

 

 

 

 

 

IN

 

 

 

 

 

 

IN

 

 

 

 

NC

COMMON

 

 

 

 

 

NC

COMMON

3

 

14

3

AD637

12

AD637

 

 

 

 

 

OUTPUT OFFSET

4

TOP VIEW

11

+VS

OUTPUT OFFSET

4

13

+V

S

 

 

TOP VIEW

 

 

CS

5

(Not to Scale)

10

–V

S

CS

5

(Not to Scale)

12

–VS

 

 

 

 

 

 

 

 

 

 

 

RMS OUT

DEN INPUT

 

 

 

 

 

RMS OUT

DEN INPUT

6

 

11

6

 

 

 

9

 

 

 

 

 

 

 

 

 

 

 

 

C

 

dB OUTPUT

 

 

 

 

 

C

 

dB OUTPUT

7

 

10

 

 

 

 

 

 

 

 

7

 

 

 

8

 

 

 

 

 

AV

 

 

 

 

 

 

AV

NC

 

 

 

NC

 

 

 

 

 

 

 

 

8

 

9

 

NC = NO CONNECT

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NC = NO CONNECT

 

 

PIN FUNCTION DESCRIPTIONS

14-Lead DIP

Pin No.

Mnemonic

Description

 

 

 

1

BUFF IN

Buffer Input

2, 12

NC

No Connection

3

COMMON

Analog Common

4

OUTPUT OFFSET

Output Offset

5

CS

Chip Select

6

DEN INPUT

Denominator Input

7

dB OUTPUT

dB Output

8

CAV

Averaging Capacitor

 

 

Connection

9

RMS OUT

rms Output

10

–VS

Negative Supply

 

 

Rail

11

+VS

Positive Supply Rail

13

VIN

Signal Input

14

BUFF OUT

Buffer Output

 

 

 

16-Lead SOIC

Pin No.

Mnemonic

Description

 

 

 

1

BUFF IN

Buffer Input

2, 8, 9, 14

NC

No Connection

3

COMMON

Analog Common

4

OUTPUT OFFSET

Output Offset

5

CS

Chip Select

6

DEN INPUT

Denominator Input

7

dB OUTPUT

dB Output

10

CAV

Averaging Capacitor

 

 

Connection

11

RMS OUT

rms Output

12

–VS

Negative Supply

 

 

Rail

13

+VS

Positive Supply Rail

15

VIN

Signal Input

16

BUFF OUT

Buffer Output

 

 

 

REV. F

–5–

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