Datasheet

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Integrated Circuit

True RMS-to-DC Converter

Data Sheet

AD536A

Rev. E

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FEATURES

True rms-to-dc conversion

Laser trimmed to high accuracy

±0.2% maximum error (AD536AK)

±0.5% maximum error (AD536AJ)

Wide response capability

Computes rms of ac and dc signals

450 kHz bandwidth: V rms > 100 mV

2 MHz bandwidth: V rms > 1 V

Signal crest factor of 7 for 1% error

dB output with 60 dB range

Low power: 1.2 mA quiescent current

Single- or dual-supply operation

Monolithic integrated circuit

−55°C to +125°C operation (AD536AS)

GENERAL DESCRIPTION

The AD536A is a complete monolithic integrated circuit that

performs true rms-to-dc conversion. It offers performance

comparable or superior to that of hybrid or modular units costing

much more. The AD536A directly computes the true rms value of

any complex input waveform containing ac and dc components.

A crest factor compensation scheme allows measurements with 1%

error at crest factors up to 7. The wide bandwidth of the device

extends the measurement capability to 300 kHz with less than 3 dB

errors for signal levels greater than 100 mV.

An important feature of the AD536A, not previously available

in rms converters, is an auxiliary dB output pin. The logarithm

of the rms output signal is brought out to a separate pin to allow

the dB conversion, with a useful dynamic range of 60 dB. Using

an externally supplied reference current, the 0 dB level can be

conveniently set to correspond to any input level from 0.1 V to

2 V rms.

The AD536A is laser trimmed to minimize input and output offset

voltage, to optimize positive and negative waveform symmetry

(dc reversal error), and to provide full-scale accuracy at 7 V rms.

As a result, no external trims are required to achieve the rated

unit accuracy.

The input and output pins are fully protected. The input circuitry

can take overload voltages well beyond the supply levels. Loss of

supply voltage with the input connected to external circuitry does

not cause the device to fail. The output is short-circuit protected.

FUNCTIONAL BLOCK DIAGRAM

BUFFER IN

25kΩ

80kΩ

25kΩ

–V

COM

AD536A

OUT

BUFFER

OUT

CURRENT

MIRROR

SQUARER/

DIVIDER

ABSOLUTE

VALUE

00504-001

BUF

Figure 1.

The AD536A is available in two accuracy grades (J and K) for

commercial temperature range (0°C to 70°C) applications, and

one grade (S) rated for the −55°C to +125°C extended range.

The AD536AK offers a maximum total error of ±2 mV ± 0.2%

of reading, while the AD536AJ and AD536AS have maximum

errors of ±5 mV ± 0.5% of reading. All three versions are available

in a hermetically sealed 14-lead DIP or a 10-pin TO-100 metal

header package. The AD536AS is also available in a 20-terminal

leadless hermetically sealed ceramic chip carrier.

The AD536A computes the true root-mean-square level of a

complex ac (or ac plus dc) input signal and provides an equiva-

lent dc output level. The true rms value of a waveform is a more

useful quantity than the average rectified value because it relates

directly to the power of the signal. The rms value of a statistical

signal also relates to its standard deviation.

An external capacitor is required to perform measurements to the

fully specified accuracy. The value of this capacitor determines the

low frequency ac accuracy, ripple amplitude, and settling time.

The AD536A operates equally well from split supplies or a

single supply with total supply levels from 5 V to 36 V. With

1 mA quiescent supply current, the device is well suited for a

wide variety of remote controllers and battery-powered

instruments.

Summary of content (17 pages)

PAGE 1
FEATURES True rms-to-dc conversion Laser trimmed to high accuracy ±0.2% maximum error (AD536AK) ±0.5% maximum error (AD536AJ) Wide response capability Computes rms of ac and dc signals 450 kHz bandwidth: V rms > 100 mV 2 MHz bandwidth: V rms > 1 V Signal crest factor of 7 for 1% error dB output with 60 dB range Low power: 1.
PAGE 2
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PAGE 3
AD536A Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Frequency Response .....................................................................9 General Description ......................................................................... 1 AC Measurement Accuracy and Crest Factor ...........................9 Functional Block Diagram ..............................................................
PAGE 4
Data Sheet AD536A SPECIFICATIONS TA = +25°C and ±15 V dc, unless otherwise noted. Table 1. Parameter TRANSFER FUNCTION CONVERSION ACCURACY Total Error, Internal Trim 1 (See Figure 13) vs. Temperature TMIN to +70°C +70°C to +125°C vs. Supply Voltage AD536AJ Typ Max VOUT = √Avg(VIN)2 Min AD536AK Typ Max VOUT = √Avg(VIN)2 mV ± % of rdg ±0.1 ± 0.01 ±0.05 ± 0.005 ±0.1 ± 0.005 ±0.3 ± 0.005 mV ± % of rdg/°C mV ± % of rdg/°C mV ± % of rdg/°C ±0.1 ± 0.01 ±0.1 ±0.01 ±0.2 ±3 ± 0.3 ±0.1 ±2 ± 0.
PAGE 5
AD536A Parameter IOUT TERMINAL IOUT Scale Factor IOUT Scale Factor Tolerance Output Resistance Voltage Compliance BUFFER AMPLIFIER Input and Output Voltage Range Input Offset Voltage, RS = 25 kΩ Input Bias Current Input Resistance Output Current Short-Circuit Current Output Resistance Small-Signal Bandwidth Slew Rate 4 POWER SUPPLY Voltage Rated Performance Dual Supply Single Supply Quiescent Current Total VS, 5 V to 36 V, TMIN to TMAX TEMPERATURE RANGE Rated Performance Storage NUMBER OF TRANSISTORS Data
PAGE 6
Data Sheet AD536A ABSOLUTE MAXIMUM RATINGS Table 2.
PAGE 7
AD536A Data Sheet PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS VIN 1 14 +VS NC 2 13 NC 12 NC –VS 3 AD536A TOP VIEW 11 NC (Not to Scale) 10 COM dB 5 BUF OUT 6 9 RL BUF IN 7 8 IOUT NC = NO CONNECT 00504-003 CAV 4 Figure 3. D-14 and Q-14 Packages Pin Configuration Table 3. D-14 and Q-14 Packages Pin Function Descriptions Pin No.
PAGE 8
+VS NC 2 1 20 19 –VS 4 NC 5 AD536A CAV 6 TOP VIEW (Not to Scale) NC 7 9 10 11 12 13 BUF OUT BUF IN NC IOUT RL dB 8 18 NC 17 NC 16 NC 15 NC 14 COM NC = NO CONNECT 00504-005 VIN 3 NC AD536A NC Data Sheet Figure 5. E-20 Package Pin Configuration Table 5. E-20 Package Pin Function Descriptions Pin No.
PAGE 9
AD536A Data Sheet THEORY OF OPERATION The AD536A embodies an implicit solution of the rms equation that overcomes the dynamic range as well as other limitations inherent in a straightforward computation of rms. The actual computation performed by the AD536A follows the equation V 2  V rms = Avg  IN   V rms  VOUT = 2R2 × I rms = VIN rms Figure 6 is a simplified schematic of the AD536A.
PAGE 10
Data Sheet AD536A VIN NC 2 –VS –VS + C1, CAV +VS C2 CAV dB 0.1µF BUF OUT dB OUT 3mV/dB BUF IN ABSOLUTE VALUE 1 14 +VS 4.6V TO 18V +E AD536A 13 NC SQUARER/ DIVIDER 3 +VS 12 NC EOUT AD580J 2.5V R4 33.2kΩ 11 NC 4 CURRENT MIRROR 5 6 10 9 25kΩ 8 BUF 7 COM RL IOUT –E R1 500kΩ 0dB REF ADJUST dB SCALE FACTOR ADJUST +VS 7 R6 24.9kΩ LINEAR rms OUTPUT R5 5kΩ 2 R3 60.
PAGE 11
AD536A Data Sheet 25 ±PEAK INPUT OR OUTPUT (V) 20 VIN 15 10 VOUT 5 20 VIN 15 VOUT 10 5 0 ±6 ±10 ±16 VOLTS (DUAL SUPPLY) ±18 0 5 10 20 30 VOLTS (SINGLE SUPPLY) Figure 12. Input and Output Voltage Ranges vs. Single Supply Figure 11. Input and Output Voltage Ranges vs. Dual Supply Rev. E | Page 10 of 16 00504-022 2.
PAGE 12
Data Sheet AD536A APPLICATIONS INFORMATION NC The AD536A is simple to connect to for the majority of high accuracy rms measurements, requiring only an external capacitor to set the averaging time constant. The standard connection is shown in Figure 13 through Figure 15. In this configuration, the AD536A measures the rms of the ac and dc levels present at the input, but shows an error for low frequency input as a function of the filter capacitor, CAV, as shown in Figure 19.
PAGE 13
AD536A Data Sheet CAV CAV 1 R1 500Ω –VS NC 2 –VS CAV VOUT dB BUF OUT 3 ABSOLUTE VALUE AD536A SQUARER/ DIVIDER 7 12 NC 11 NC CURRENT MIRROR 6 BUF IN 13 NC 4 5 14 25kΩ BUF 25kΩ 10 9 8 COM RL C2 1µF VIN +VS +VS NONPOLARIZED R4 OFFSET 50kΩ ADJUST VIN –VS CAV R3 750kΩ dB VOUT R2 365Ω BUF OUT RL BUF IN 10kΩ TO 1kΩ IOUT 1 NC 2 –VS 00504-007 VIN +VS 3 ABSOLUTE VALUE +VS 13 NC SQUARER/ DIVIDER 12 NC 20kΩ 11 NC CURRENT MIRROR 6 7 +VS 0.
PAGE 14
Data Sheet AD536A The primary disadvantage in using a large CAV to remove ripple is that the settling time for a step change in input level is increased proportionately. Figure 19 illustrates that the relationship between CAV and 1% settling time is 115 ms for each microfarad of CAV. The settling time is twice as great for decreasing signals as it is for increasing signals. The values in Figure 19 are for decreasing signals. Settling time also increases for low signal levels, as shown in Figure 20.
PAGE 15
AD536A Data Sheet OUTLINE DIMENSIONS 0.005 (0.13) MIN 0.080 (2.03) MAX 8 14 1 PIN 1 0.310 (7.87) 0.220 (5.59) 7 0.100 (2.54) BSC 0.765 (19.43) MAX 0.200 (5.08) MAX 0.200 (5.08) 0.125 (3.18) 0.023 (0.58) 0.014 (0.36) 0.320 (8.13) 0.290 (7.37) 0.060 (1.52) 0.015 (0.38) 0.150 (3.81) MIN SEATING PLANE 0.070 (1.78) 0.030 (0.76) 0.015 (0.38) 0.008 (0.
PAGE 16
Data Sheet AD536A REFERENCE PLANE 0.500 (12.70) MIN 0.185 (4.70) 0.165 (4.19) 0.160 (4.06) 0.110 (2.79) 0.335 (8.51) 0.305 (7.75) 0.370 (9.40) 0.335 (8.51) 6 7 5 0.021 (0.53) 0.016 (0.40) 0.115 (2.92) BSC 8 4 9 0.045 (1.14) 0.025 (0.65) 3 2 0.040 (1.02) MAX BASE & SEATING PLANE 10 1 0.034 (0.86) 0.025 (0.64) 0.230 (5.