LH0091 True RMS to DC Converter General Description Features The LH0091, rms to dc converter generates a dc output equal to the rms value of any input per the transfer function: Y Y Y EOUT(DC) e 0# 1 T EIN2(t) dt T 0 Y Y Y The device provides rms conversion to an accuracy of 0.1% of reading using the external trim procedure. It is possible to trim for maximum accuracy (0.5 mV g 0.05% typ) for decade ranges i.e., 10 mV x 100 mV, 0.7V x 7V, etc. Y Y Low cost True rms conversion 0.5% of reading accuracy untrimmed 0.05% of reading accuracy with external trim Minimum component count Input voltage to g 15V peak for VS e g 15V Uncommitted amplifier for filtering, gain, or high crest factor configuration Military or commercial temperature range. Block and Connection Diagrams Dual-In-Line Package Dual-In-Line Package Order Number LH0091CD See Package D16D TL/H/5694 – 1 Simplified Schematic TL/H/5694 – 2 Note: Dotted lines denote external connections. C1995 National Semiconductor Corporation TL/H/5694 RRD-B30M115/Printed in U. S. A. LH0091 True RMS to DC Converter September 1993 Absolute Maximum Ratings Operating Temperature Range LH0091C If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. Supply Voltage Storage Temperature Range LH0091C g 22V Input Voltage Output Short Circuit Duration TMIN b 25§ C g 15V peak TMAX 85§ C b 25§ C to a 85§ C Lead Temp. (Soldering, 10 seconds) 260§ C Continuous Electrical Characteristics VS e g 15V, TA e 25§ C unless otherwise noted Transfer Function e EO(DC) e 0T# E 1 T 0 2 IN (t) dt Parameter Conditions Min Typ Max Units ACCURACY (See Definition of Terms) Total Unadjusted Error 50 mVrmssVINs7Vrms (Figure 1) 20, g 0.5 40, g 1.0 mV, % Total Adjusted Error 50 mVrmssVINs7Vrms (Figure 3) 0.5, g 0.05 1, g 0.2 mV, % Total Unadjusted Error vs Temperature b 25§ C s TA s a 70§ C Total Unadjusted Error vs Supply Voltage 0.25, g 0.2% mV, %/§ C 1 mV/V AC PERFORMANCE Frequency for Specified Adjusted Error Input e 7Vrms, Sinewave (Figure 3) Input e 0.7Vrms, Sinewave (Figure 3) Input e 0.1Vrms, Sinewave (Figure 3) 30 70 40 20 kHz KHz kHz Frequency for 1% Additional Error Input e 7Vrms, Sinewave (Figure 3) Input e 0.7Vrms, Sinewave (Figure 3) Input e 0.1Vrms, Sinewave (Figure 3) 100 200 75 50 kHz kHz kHz Bandwidth (3 dB) Input e 7Vrms, Sinewave (Figure 3) Input e 0.7Vrms, Sinewave (Figure 3) Input e 0.1Vrms, Sinewave (Figure 3) 2 1.5 0.8 MHz MHz MHz Crest Factor Rated Adjusted Accuracy Using the High Crest Factor Circuit (Figure 5) 5 10 INPUT CHARACTERISTICS Input Voltage Range For Rated Performance Input Impedance g 0.05 4.5 g 11 Vpeak 5 kX Output Short Circuit Current 22 mA Output Impedance 1 X OUTPUT CHARACTERISTICS Rated Output Voltage RLt2.5 kX 10 V POWER SUPPLY REQUIREMENTS Operating Range Quiescent Current g5 VS e g 15V 14 2 g 20 V 18 mA Op Amp Electrical Characteristics VS e g 15V, TA e 25§ C unless otherwise noted Parameter Conditions Typ Max Units 1.0 10 mV 4.0 200 nA Input Bias Current 30 500 Input Resistance 2.5 MX 15 160 V/mv g 10 g 13 V RSs10 kX 90 dB RSs10 kX 96 dB 25 mA Slew Rate (Unity Gain) 0.5 V/ms Small Signal Bandwidth 1.0 MHz VOS Input Offset Voltage IOS Input Offset Current IB RIN AOL Large Signal Voltage Gain VOUT e g 10V, RLt2 kX VO Output Voltage Swing R e 10 kX VI Input Voltage Range CMRR Common-Mode Rejection Ratio PSRR Supply Voltage Rejection Ratio ISC Output Short-Circuit Current Sr BW Min RSs10 kX nA g 10 V Typical Performance Characteristics Error vs Frequency Error vs Frequency Error vs Crest Factor TL/H/5694 – 3 Typical Applications (All applications require power supply by-pass capacitors.) TL/H/5694 – 4 CEXT t 1mF; frequency t 1 kHz FIGURE 1. LH0091 Basic Connection (No Trim) 3 Typical Applications (Continued) RT e 240k CEXT t 1mF, f t 1 kHz Note. The easy trim procedure is used for ac coupled input signals. It involves two trims and can achieve accuracies of 2 mV offset g 0.1% reading. Procedure: 1. Apply 100 mV rms (sine wave) to input, adjust R3 until the output reads 100 mVDC. 2. Apply 5 Vrms (sine wave) to input, adjust R4 until the output reads 5 VDC. 3. Repeat steps 1 and 2 until the desired initial accuracy is achieved. FIGURE 2. LH0091 ‘‘Easy Trim’’ (For ac Inputs Only) R1 e dc symmetry balance R2 e Input offset Note. This procedure will give accuracies of 0.5 mV offset g 0.05% reading for inputs from 0.05V peak to 10V peak. R3 e Output offset Procedure: 1. Apply 50 mVDC to the input. Read and record the output. R4 e Gain adjust 2. Apply b 50 mVDC to the input. Use R2 to adjust for an output of the same magnitude as in step 1. 3. Apply 50 mV to the input. Use R3 to adjust the output for 50 mV. 4. Apply b 50 mV to input. Use R2 to adjust the output for 50 mV. 5. Apply g 10V alternately to the input. Adjust R1 until the output readings for both polarities are equal (not necessary that they be exactly 10V). 6. Apply 10V to the input. Use R4 to adjust for 10V at the output. 7. Repeat this procedure to obtain the desired accuracy. FIGURE 3. LH0091 Standard dc Trim Procedure Note. The additional op amp in the LH0091 may be used as a low pass filter as shown in Figure 4. R1 e R2 e 16k C1 e C2 e 1mF fO j 10 Hz TL/H/5694 – 6 FIGURE 4. Output Filter Connection Using the Internal Op Amp 4 Typical Applications (Continued) Note. When converting signals with a crest factor t 2, the LH0091 should be connected as shown. Note that this circuit utilizes a 20k resistor to drop the input current by a factor of five. The frequency response will correspond to a voltage which is 1/5 eIN. Note that the extra op amp in the LH0091 may be used to build a gain of 5 amplifier to restore the output voltage. TL/H/5694 – 7 Note. Response time of the dc output voltage is dominated by the RC time constant consisting of the total resistance between pins 9 and 10 and the external capacitor, CEX. FIGURE 5. High Crest Factor Circuit Definition of Terms Frequency for Specified Error: The error at low frequency is governed by the size of the external averaging capacitor. At high frequencies, error is dependent on the frequency response of the internal circuitry. The frequency for specified error is the maximum input frequency for which the output will be within the specified error band (i.e., frequency for 1% error means the input frequency must be less than 200 kHz to maintain an output with an error of less than 1% of the initial reading. True rms to dc Converter: A device which converts any signal (ac, dc, ac a dc) to the dc equivalent of the rms value. Error: is the amount by which the actual output differs from the theoretical value. Error is defined as a sum of a fixed term and a percent of reading term. The fixed term remains constant, regardless of input while the percent of reading term varies with the input. Total Unadjusted Error: The total error of the device without any external adjustments. Crest Factor: is the peak value of a waveform divided by the rms value of the same waveform. For high crest factor signals, the performance of the LH0091 can be improved by using the high crest factor connection. Bandwidth: The frequency at which the output dc voltage drops to 0.707 of the dc value at low frequency. 5 LH0091 True RMS to DC Converter Physical Dimensions inches (millimeters) Dual-In-Line Package Order Number LH0091CD NS Package D16D LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Corporation 1111 West Bardin Road Arlington, TX 76017 Tel: 1(800) 272-9959 Fax: 1(800) 737-7018 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Europe Fax: (a49) 0-180-530 85 86 Email: cnjwge @ tevm2.nsc.com Deutsch Tel: (a49) 0-180-530 85 85 English Tel: (a49) 0-180-532 78 32 Fran3ais Tel: (a49) 0-180-532 93 58 Italiano Tel: (a49) 0-180-534 16 80 National Semiconductor Hong Kong Ltd. 13th Floor, Straight Block, Ocean Centre, 5 Canton Rd. Tsimshatsui, Kowloon Hong Kong Tel: (852) 2737-1600 Fax: (852) 2736-9960 National Semiconductor Japan Ltd. Tel: 81-043-299-2309 Fax: 81-043-299-2408 National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.