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 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 to +125°C operation (AD536AS)
The 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 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 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 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.
The AD536A is available in two accuracy grades (J and K) for commercial temperature range to 70°C) applications, and one grade (S) rated for the to +125°C extended range. The AD536AK offers a maximum total error 0.2% of reading, while the AD536AJ and AD536AS have maximum errors 0.5% of reading. All three versions are available in a hermetically sealed 14-lead DIP 10-pin TO-100 metal header package. The AD536AS is also available 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 equivalent 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 36 V. With 1 mA quiescent supply current, the device is well suited for a wide variety of remote controllers and battery-powered instruments.
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Features : 1 General Description : 1 Functional Block Diagram : 1 Revision History : 2 Specifications : 3 Absolute Maximum Ratings : 5
ESD Caution : 5 Pin Configurations and Function Descriptions : 6 Theory of Operation : 8
F to Rev. G Changes to Figure 5 and Table : 7 Change to Figure : 12 Changes to Ordering Guide : 15
E to Rev. F Change to Figure : 1 Changes to Table : 3 Change to Figure : 12 Changes to Ordering Guide : 15
D to Rev. E Reorganized Layout : Universal Changes to Figure : 1 Changes to Figure : 8 Changes to Figure : 9 Changes to Figure 13, Figure 14, and Figure : 11 Changes to Figure 16, Figure 17, and Single-Supply Operation Section : 12 Changes to Figure : 13 Updated Outline Dimensions : 14
C to Rev. D Changes to Features Section : 1 Changes to General Description Section : 1 Changes to Figure : 1 Changes to Table : 5
Frequency Response 9 AC Measurement Accuracy and Crest Factor : 9 Applications Information : 11 Typical Connections : 11 Optional External Trims For High Accuracy : 11 Single-Supply Operation : 12 Choosing the Averaging Time Constant : 12 Outline Dimensions : 14 Ordering Guide : 15
Change to Figure : 5 Changes to Figure : 10 Changes to Connections for dB Operation Section : 11 Changes to Figure : 12 Changes to Frequency Response Section : 12 Updated Outline Dimensions : 14 Changes to Ordering Guide : 15
B to Rev. C Updated Format : Universal Changed Product Description to General Description : 1 Changes to General Description : 1 Changes to Table : 3 Changes to Table : 5 Added Pin Configurations and Function Descriptions : 6 Changed Standard Connection to Typical Connections : 8 Changed Single Supply Connection to Single Supply Operation : 9 Changes to Connections for dB Operation : 11 Changes to Figure : 12 Updated Outline Dimensions : 14 Changes to Ordering Guide : 15
SPECIFICATIONS
Total Error, Internal Trim1 (See Figure 13) vs. Temperature TMIN to +70°C
vs. Supply Voltage DC Reversal Error Total Error, External Trim1 (See Figure 16) ERROR VS. CREST FACTOR2 Crest Factor 1 to Crest Factor 2 Crest Factor = 3 Crest Factor = 7 FREQUENCY RESPONSE3 Bandwidth for 1% Additional Error (0.09 dB) VIN 10 mV VIN 100 mV VIN ±3 dB Bandwidth VIN 10 mV VIN 100 mV VIN 1 V
INPUT CHARACTERISTICS Signal Range, ±15 V Supplies Continuous RMS Level Peak Transient Input Continuous RMS Level, ±5 V Peak Transient Input, ±5 V Maximum Continuous Nondestructive Input Level (All Supply Voltages) Input Resistance Input Offset Voltage
OUTPUT CHARACTERISTICS Offset Voltage, VIN = COM (See Figure 13) vs. Temperature vs. Supply Voltage Swing, ±15 V Supplies 5 V Supply
dB OUTPUT, 1 V rms (See Figure 7) Error, mV < VIN 7 V rms Scale Factor Scale Factor Temperature Coefficient Uncompensated IREF for 1 V rms IREF Range
Required
