a |
High Precision, Wideband |
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RMS-to-DC Converter |
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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 |
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Cerdip (Q) Packages |
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BUFFER |
AD637 |
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BUFFER |
AD637 |
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1 |
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14 |
1 |
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16 |
2 |
ABSOLUTE |
13 |
2 |
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ABSOLUTE |
15 |
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VALUE |
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VALUE |
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3 |
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12 |
3 |
BIAS |
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14 |
BIAS |
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SECTION |
SQUARER/DIVIDER |
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4 |
SECTION |
SQUARER/DIVIDER |
13 |
4 |
11 |
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25k |
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5 |
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25k |
12 |
5 |
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10 |
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25k |
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9 |
6 |
25k |
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11 |
6 |
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7 |
FILTER |
8 |
7 |
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FILTER |
10 |
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8 |
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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.)
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AD637J/A |
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AD637K/B |
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AD637S |
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Model |
Min |
Typ |
Max |
Min |
Typ |
Max |
Min |
Typ |
Max |
Unit |
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TRANSFER FUNCTION |
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VOUT = avg × (VIN )2 |
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VOUT = avg × (VIN )2 |
VOUT = |
avg × (VIN )2 |
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CONVERSION ACCURACY |
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mV ± % of Reading |
Total Error, Internal Trim1 (Fig. 2) |
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1 0.5 |
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0.5 0.2 |
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1 0.5 |
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TMIN to TMAX |
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3.0 0.6 |
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2.0 0.3 |
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6 0.7 |
mV ± % of Reading |
vs. Supply, + VIN = +300 mV |
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30 |
150 |
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30 |
150 |
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30 |
150 |
µV/V |
vs. Supply, – VIN = –300 mV |
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100 |
300 |
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100 |
300 |
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100 |
300 |
µV/V |
DC Reversal Error at 2 V |
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0.25 |
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0.1 |
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0.25 |
% of Reading |
Nonlinearity 2 V Full Scale2 |
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0.04 |
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0.02 |
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0.04 |
% of FSR |
Nonlinearity 7 V Full Scale |
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0.05 |
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0.05 |
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0.05 |
% of FSR |
Total Error, External Trim |
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± 0.5 ± 0.1 |
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± 0.25 ± 0.05 |
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± 0.5 ± 0.1 |
mV ± % of Reading |
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ERROR VS. CREST FACTOR3 |
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Crest Factor 1 to 2 |
Specified Accuracy |
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Specified Accuracy |
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Specified Accuracy |
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Crest Factor = 3 |
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± 0.1 |
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± 0.1 |
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± 0.1 |
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% of Reading |
Crest Factor = 10 |
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± 1.0 |
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± 1.0 |
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± 1.0 |
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% of Reading |
AVERAGING TIME CONSTANT |
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25 |
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25 |
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25 |
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ms/µF CAV |
INPUT CHARACTERISTICS |
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Signal Range, ± 15 V Supply |
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Continuous RMS Level |
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0 to 7 |
± 15 |
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0 to 7 |
± 15 |
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0 to 7 |
± 15 |
V rms |
Peak Transient Input |
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V p-p |
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Signal Range, ± 5 V Supply |
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Continuous rms Level |
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0 to 4 |
± 6 |
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0 to 4 |
± 6 |
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0 to 4 |
± 6 |
V rms |
Peak Transient Input |
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V p-p |
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Maximum Continuous Nondestructive |
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± 15 |
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± 15 |
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± 15 |
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Input Level (All Supply Voltages) |
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V p-p |
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Input Resistance |
6.4 |
8 |
9.6 |
6.4 |
8 |
9.6 |
6.4 |
8 |
9.6 |
kΩ |
Input Offset Voltage |
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± 0.5 |
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± 0.2 |
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± 0.5 |
mV |
FREQUENCY RESPONSE4 |
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Bandwidth for 1% Additional Error (0.09 dB) |
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VIN = 20 mV |
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11 |
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11 |
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11 |
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kHz |
VIN = 200 mV |
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66 |
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66 |
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66 |
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kHz |
VIN = 2 V |
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200 |
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200 |
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200 |
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kHz |
± 3 dB Bandwidth |
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VIN = 20 mV |
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150 |
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150 |
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150 |
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kHz |
VIN = 200 mV |
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1 |
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1 |
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1 |
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MHz |
VIN = 2 V |
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8 |
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8 |
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8 |
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MHz |
OUTPUT CHARACTERISTICS |
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1 |
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0.5 |
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1 |
mV |
Offset Voltage |
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vs. Temperature |
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± 0.05 |
0.089 |
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± 0.04 |
0.056 |
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± 0.04 |
0.07 |
mV/°C |
Voltage Swing, ± 15 V Supply, |
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2 kΩ Load |
0 to 12.0 |
13.5 |
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0 to 12.0 |
13.5 |
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0 to 12.0 |
13.5 |
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V |
Voltage Swing, ± 3 V Supply, |
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2 kΩ Load |
0 to 2 |
2.2 |
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0 to 2 |
2.2 |
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0 to 2 |
2.2 |
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V |
Output Current |
6 |
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6 |
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6 |
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mA |
Short Circuit Current |
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20 |
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20 |
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20 |
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mA |
Resistance, Chip Select “High” |
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0.5 |
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0.5 |
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0.5 |
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Ω |
Resistance, Chip Select “Low” |
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100 |
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100 |
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100 |
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kΩ |
dB OUTPUT |
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± 0.5 |
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± 0.3 |
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± 0.5 |
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Error, VIN 7 mV to 7 V rms, |
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dB |
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0 dB = 1 V rms |
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Scale Factor |
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–3 |
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–3 |
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–3 |
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mV/dB |
Scale Factor Temperature Coefficient |
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+0.33 |
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+0.33 |
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+0.33 |
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% of Reading/°C |
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–0.033 |
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–0.033 |
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–0.033 |
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dB/°C |
IREF for 0 dB = 1 V rms |
5 |
20 |
80 |
5 |
20 |
80 |
5 |
20 |
80 |
µA |
IREF Range |
1 |
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100 |
1 |
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100 |
1 |
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100 |
µA |
BUFFER AMPLIFIER |
–VS to (+VS – 2.5 V) |
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–VS to (+VS – 2.5 V) |
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–VS to (+VS – 2.5 V) |
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V |
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Input Output Voltage Range |
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Input Offset Voltage |
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± 0.8 |
2 |
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± 0.5 |
1 |
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± 0.8 |
2 |
mV |
Input Current |
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± 2 |
10 |
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± 2 |
5 |
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± 2 |
10 |
nA |
Input Resistance |
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108 |
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108 |
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108 |
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Ω |
Output Current |
(+5 mA, –130 µA) |
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(+5 mA, –130 µA) |
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(+5 mA, –130 µA) |
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Short Circuit Current |
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20 |
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20 |
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20 |
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mA |
Small Signal Bandwidth |
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1 |
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1 |
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1 |
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MHz |
Slew Rate5 |
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5 |
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5 |
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5 |
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V/µs |
DENOMINATOR INPUT |
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Input Range |
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0 to 10 |
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0 to 10 |
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0 to 10 |
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V |
Input Resistance |
20 |
25 |
30 |
20 |
25 |
30 |
20 |
25 |
30 |
kΩ |
Offset Voltage |
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± 0.2 |
± 0.5 |
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± 0.2 |
± 0.5 |
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± 0.2 |
± 0.5 |
mV |
–2– |
REV. F |
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AD637 |
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AD637J/A |
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AD637K/B |
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AD637S |
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Model |
Min |
Typ |
Max |
Min |
Typ |
Max |
Min |
Typ |
Max |
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Unit |
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CHIP SELECT PROVISION (CS) |
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RMS “ON” Level |
Open or 2.4 V < VC < +VS |
Open or 2.4 V < VC < +VS |
Open or 2.4 V < VC < +VS |
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RMS “OFF” Level |
VC < 0.2 V |
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VC < 0.2 V |
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VC < 0.2 V |
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IOUT of Chip Select |
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CS “Low” |
10 |
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10 |
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10 |
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µA |
CS “High” |
Zero |
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Zero |
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Zero |
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On Time Constant |
10 µs + ((25 kΩ) CAV) |
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10 µs + ((25 kΩ) CAV) |
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10 µs + ((25 kΩ) CAV) |
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Off Time Constant |
10 µs + ((25 kΩ) CAV) |
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10 µs + ((25 kΩ) CAV) |
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10 µs + ((25 kΩ) CAV) |
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POWER SUPPLY |
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Operating Voltage Range |
± 3.0 |
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18 |
3.0 |
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18 |
3.0 |
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18 |
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V |
Quiescent Current |
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2.2 |
3 |
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2.2 |
3 |
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2.2 |
3 |
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mA |
Standby Current |
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350 |
450 |
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350 |
450 |
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350 |
450 |
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µA |
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TRANSISTOR COUNT |
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107 |
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107 |
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107 |
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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– |
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
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Temperature |
Package |
Package |
Model |
Range |
Description |
Option |
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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 |
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5962-8963701CA* |
–55°C to +125°C |
Cerdip |
Q-14 |
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*A standard microcircuit drawing is available.
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FILTER/AMPLIFIER |
CAV |
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BUFF OUT |
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ONE QUADRANT |
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24k |
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BUFF IN |
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SQUARER/DIVIDER |
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+VS |
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BUFFER |
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A5 |
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AMPLIFIER |
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A4 |
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RMS |
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I4 |
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OUT |
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I1 |
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dB |
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24k |
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OUT |
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Q4 |
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COM |
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ABSOLUTE VALUE VOLTAGE – |
Q1 |
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Q5 |
BIAS |
CS |
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CURRENT CONVERTER |
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DEN |
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6k |
6k |
Q2 |
Q3 |
A3 |
I3 |
24k |
INPUT |
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OUTPUT |
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A2 |
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OFFSET |
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12k |
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125 |
AD637 |
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VIN |
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A1 |
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–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 |
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AD637 |
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PIN CONFIGURATIONS |
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14-Lead DIP |
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16-Lead SOIC |
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BUFF IN |
1 |
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14 |
BUFF OUT |
BUFF IN |
1 |
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16 |
BUFF OUT |
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V |
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V |
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NC |
2 |
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15 |
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NC |
2 |
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13 |
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IN |
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IN |
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NC |
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COMMON |
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NC |
COMMON |
3 |
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14 |
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3 |
AD637 |
12 |
AD637 |
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OUTPUT OFFSET |
4 |
TOP VIEW |
11 |
+VS |
OUTPUT OFFSET |
4 |
13 |
+V |
S |
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TOP VIEW |
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CS |
5 |
(Not to Scale) |
10 |
–V |
S |
CS |
5 |
(Not to Scale) |
12 |
–VS |
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RMS OUT |
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DEN INPUT |
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RMS OUT |
DEN INPUT |
6 |
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11 |
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6 |
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9 |
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C |
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dB OUTPUT |
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C |
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dB OUTPUT |
7 |
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10 |
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7 |
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8 |
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AV |
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AV |
NC |
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NC |
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8 |
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9 |
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NC = NO CONNECT |
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NC = NO CONNECT |
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PIN FUNCTION DESCRIPTIONS
14-Lead DIP
Pin No. |
Mnemonic |
Description |
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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 |
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Connection |
9 |
RMS OUT |
rms Output |
10 |
–VS |
Negative Supply |
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Rail |
11 |
+VS |
Positive Supply Rail |
13 |
VIN |
Signal Input |
14 |
BUFF OUT |
Buffer Output |
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16-Lead SOIC
Pin No. |
Mnemonic |
Description |
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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 |
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Connection |
11 |
RMS OUT |
rms Output |
12 |
–VS |
Negative Supply |
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Rail |
13 |
+VS |
Positive Supply Rail |
15 |
VIN |
Signal Input |
16 |
BUFF OUT |
Buffer Output |
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REV. F |
–5– |