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19-0824; Rev 2; 3/96
True RMS-to-DC Converters
General Description
The MX536A and MX636 are true RMS-to-DC converters. They feature low power and are designed to accept low-level input signals from 0 to 7VRMS for the MX536A and 0 to 200mVRMS for the MX636. Both devices accept complex input waveforms containing AC and DC components. They can be operated from either a single supply or dual supplies. Both devices draw less than 1mA of quiescent supply current, making them ideal for battery-powered applications. Input and output offset, positive and negative waveform symmetry (DC reversal), and full-scale accuracy are laser trimmed, so that no external trims are required to achieve full rated accuracy.
____________________________Features
o True RMS-to-DC Conversion o Computes RMS of AC and DC Signals o Wide Response: 2MHz Bandwidth for VRMS > 1V (MX536A) 1MHz Bandwidth for VRMS > 100mV (MX636) o Auxiliary dB Output: 60dB Range (MX536A) 50dB Range (MX636) o Single- or Dual-Supply Operation o Low Power: 1.2mA typ (MX536A) 800A typ (MX636)
MX536A/MX636
Ordering Information
PART MX536AJC/D MX536AJCWE MX536AJD MX536AJH MX536AJN MX536AJQ* MX536AKCWE MX536AKD MX536AKH MX536AKN MX536AKQ* MX536ASD TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C -55C to +125C PIN-PACKAGE Dice** 16 Wide SO 14 Ceramic 10 TO-100 14 Plastic DIP 14 CERDIP 16 Wide SO 14 Ceramic 10 TO-100 14 Plastic DIP 14 CERDIP 14 Ceramic
________________________Applications
Digital Multimeters Battery-Powered Instruments Panel Meters Process Control
Pin Configurations
TOP VIEW
IOUT 10
RL 1 COMMON 2 +VS 3 VIN 4
9 BUF IN 8 BUF OUT
MX536A MX636B
5 -VS
7 dB 6 CAV
Ordering Information continued at end of data sheet. * Maxim reserves the right to ship ceramic packages in lieu of CERDIP packages. ** Dice are specified at TA = +25C.
_________Typical Operating Circuits
CAV
TO-100
VIN 1 N.C. 2 -VS 3 CAV 4 dB 5 BUF OUT 6 BUF IN 7
14 +VS 13 N.C. 12 N.C.
VIN
1 2
ABSOLUTE VALUE SQUARER DIVIDER
14 13 12 11
+VS
-VS
MX536A MX636
3 4 5
11 N.C. 10 COMMON 9 8 RL IOUT VOUT
CURRENT MIRROR
10 9
6 7
BUF
8
DIP
Pin Configurations continued at end of data sheet.
Typical Operating Circuits continued at end of data sheet.
1
________________________________________________________________ Maxim Integrated Products
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True RMS-to-DC Converters MX536A/MX636
ABSOLUTE MAXIMUM RATINGS
Supply Voltage: Dual Supplies (MX536A) ............................18V (MX636) .............................12V Single Supply (MX536A) ...........................+36V (MX636) .............................+24V Input Voltage (MX536A).......................................................25V (MX636) .........................................................12V Power Dissipation (Package) Plastic DIP (derate 12mW/C above +75C) ...............450mW Small Outline (derate 10mW/C above +75C)............400mW Ceramic (derate 10mW/C above +75C) ...................500mW TO-100 metal can (derate 7mW/C above +75C) ......450mW Output Short-Circuit Duration ........................................Indefinite Operating Temperature Ranges Commercial (J, K) ...............................................0C to +70C Military (S) ......................................................-55C to +125C Storage Temperature Range .............................-55C to +150C Lead Temperature (soldering, 10sec)................................300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS--MX536A
(TA = +25C, +VS = +15V, -VS = -15V, unless otherwise noted.) PARAMETER Transfer Equation Averaging Time Constant CONVERSION ACCURACY Total Error, Internal Trim (Note 1) MX536AJ, AS MX536AK MX536AJ Total Error vs. Temperature TMIN to +70C +70C to +125C Total Error vs. Supply Total Error vs. DC Reversal Total Error, External Trim (Note 1) MX536AJ, AS MX536AK MX536AJ, AS MX536AK Crest Factor 1 to 2 Additional Error FREQUENCY RESPONSE (Note 3) Bandwidth for 1% Additional Error (0.09dB) VIN = 10mV VIN = 100mV VIN = 1V VIN = 10mV 3dB Bandwidth VIN = 100mV VIN = 1V 5 45 120 90 450 2.3 kHz MHz kHz Crest Factor = 3 Crest Factor = 7 MX536AK MX536AS MX536AS 5 0.5 2 0.2 0.1 0.01 0.05 0.005 0.1 0.005 0.03 0.005 0.1 0.01 0.2 0.1 3 0.3 2 0.1 Specified Accuracy -0.1 -1.0 % of Reading mV % of Reading/V % of Reading mV % of Reading mV % of Reading/C mV % of Reading Figure 3 CONDITIONS MIN TYP 25 MAX UNITS ms/F CAV VOUT = [avg. (VIN)2] 1/2
ERROR vs. CREST FACTOR (Note 2)
2
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True RMS-to-DC Converters
ELECTRICAL CHARACTERISTICS--MX536A (continued)
(TA = +25C, +VS = +15V, -VS = -15V, unless otherwise noted.) PARAMETER INPUT CHARACTERISTICS 15V Supplies Continuous RMS Peak Transient Input Signal Range 5V Supplies Continuous RMS Peak Transient Safe Input Input Resistance Input Offset Voltage OUTPUT CHARACTERISTICS MX536AJ TA = +25C Offset Voltage MX536AK MX536AS TA = TMIN to TMAX Supply Voltage Output Voltage Swing Output Current Short Circuit Current Output Resistance dB OUTPUT MX536AJ Error Scale Factor Scale Factor TC (Uncompensated) IREF IREF Range IOUT TERMINAL IOUT Scale Factor IOUT Scale Factor Tolerance Output Resistance Voltage Compliance 20 40 10 25 -VS to (+VS - 2.5) 20 30 A/VRMS % k V 0dB = 1VRMS 5 1 VIN = 7mV to 7VRMS, 0dB = 1VRMS MX536AK MX536AS 0.4 0.2 0.5 -3 0.33 20 80 100 0.6 0.3 0.6 mV/dB % of Reading/C A A dB 15V Supplies 5V Supplies Source Sink MX536AJ, AK MX536AS MX536AJ, AK MX536AS 0 to 11 0 to 2 5 -130 20 0.5 0.1 0.2 12.5 0.1 0.2 1 0.5 2 1 2 mV/C mV/V V mA A mA mV MX536AJ, AS MX536AK All Supplies 13.33 16.7 0.8 0.5 0 to 7 20 0 to 2 7 25 20.00 2 1 VRMS VPK VRMS VPK VPK k mV CONDITIONS MIN TYP MAX UNITS
MX536A/MX636
3
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True RMS-to-DC Converters MX536A/MX636
ELECTRICAL CHARACTERISTICS--MX536A (continued)
(TA = +25C, +VS = +15V, -VS = -15V, unless otherwise noted.) PARAMETER BUFFER AMPLIFIER Input and Output Voltage Range Input Offset Voltage Input Bias Current Input Resistance Output Current Short-Circuit Current Small-Signal Bandwidth Slew Rate (Note 4) Source Sink +5 -130 20 1 5 RS = 25k -VS to (+VS - 2.5) 0.5 20 108 4 300 V mV nA mA A mA MHz V/s CONDITIONS MIN TYP MAX UNITS
ELECTRICAL CHARACTERISTICS--MX636
(TA = +25C, +VS = +3V, -VS = -5V, unless otherwise noted.) PARAMETER Transfer Equation Averaging Time Constant CONVERSION ACCURACY Total Error, Internal Trim (Notes 5, 6) Total Error vs. Temperature (0C to +70C) Total Error vs. Supply Total Error vs. DC Reversal Total Error, External Trim (Note 5) VIN = 200mV MX636J MX636K Crest Factor 1 to 2 Additional Error Crest Factor = 3 Crest Factor = 6 FREQUENCY RESPONSE (Notes 6, 8) Bandwidth for 1% Additional Error (0.09dB) VIN = 10mV VIN = 100mV VIN = 200mV VIN = 10mV 3dB Bandwidth VIN = 100mV VIN = 200mV 14 90 130 100 900 1.5 kHz MHz kHz MX636J MX636K MX636J MX636K MX636J MX636K 0.5 1.0 0.2 0.5 0.1 0.01 0.1 0.005 0.1 0.01 0.2 0.1 0.3 0.1 0.1 0.1 Specified Accuracy -0.2 -0.5 % of Reading mV % of Reading mV % of Reading/C mV % of Reading/V % of Reading mV % of Reading Figure 3 CONDITIONS MIN TYP 25 MAX UNITS ms/F CAV
VOUT = [avg. (VIN)2]1/2
ERROR vs. CREST FACTOR (Note 3)
4
_______________________________________________________________________________________
True RMS-to-DC Converters
ELECTRICAL CHARACTERISTICS--MX636 (continued)
(TA = +25C, +VS = +3V, -VS = -5V, unless otherwise noted.) PARAMETER INPUT CHARACTERISTICS CONDITIONS Continuous RMS, All Supplies +3V, -5V Supplies Peak Transient 2.5V Supplies 5V Supplies All Supplies 5.33 MIN TYP 0 to 200 2.8 2 5 12 6.7 8.00 0.5 0.2 0.5 0.2 10 0.1 0 to 1 0 to 1 8 MX636J MX636K 1.4 10 0.3 0.1 -3 +0.33 -0.033 4 12 0.5 0.2 MAX UNITS mVRMS VPK VPK k mV
MX536A/MX636
Input Signal Range
Safe Input Input Resistance
MX636J Input Offset Voltage MX636K OUTPUT CHARACTERISTICS (Note 5) TA = +25C Offset Voltage TA = TMIN to TMAX With Supply Voltage +3V, -5V Supplies 5V to 16.5V Supplies MX636J MX636K
mV V/C mV/V V k
Output Voltage Swing Output Resistance dB OUTPUT Error Scale Factor Scale Factor Tempco IREF IREF Range IOUT TERMINAL IOUT Scale Factor IOUT Scale Factor Tolerance Output Resistance Voltage Compliance BUFFER AMPLIFIER Input and Output Voltage Range Input Offset Voltage Input Current Input Resistance Output Current Short-Circuit Current Small-Signal Bandwidth Slew Rate (Note 9)
7mV VIN 300mV
dB mV/dB %/C dB/C A A A/VRMS
0dB = 1VRMS
2 1
8 50
100 -20 8 10 10 -VS to (+VS - 2.0) -VS to (+VS - 2) RS = 10k MX636J MX636K 0.8 0.5 100 108 Source Sink +5 -130 20 1 5 2 1 300 +20 12
% k V
V mV nA mA A mA MHz V/s
_______________________________________________________________________________________
5
True RMS-to-DC Converters MX536A/MX636
ELECTRICAL CHARACTERISTICS--MX636 (continued)
(TA = +25C, +VS = +3V, -VS = -5V, unless otherwise noted.) PARAMETER POWER SUPPLY Rated Performance Dual Supplies Single Supply Quiescent Current (Note 10) CONDITIONS MIN TYP +3/-5 +2/-2.5 +5 0.8 16.5 +24 1 MAX UNITS V V V mA
Note 1: Accuracy is specified for 0 to 7VRMS, DC or 1kHz sine-wave input with the MX536A connected as in Figure 2. Note 2: Error vs. crest factor is specified as an additional error for 1VRMS rectangular pulse stream, pulse width = 200s. Note 3: Input voltages are expressed in volts RMS, and error as % of reading. Note 4: With 2k external pull-down resistor. Note 5: Accuracy is specified for 0 to 200mV, DC or 1kHz sine-wave input. Accuracy is degraded at higher RMS signal levels. Note 6: Measured at pin 8 of DIP and SO (IOUT), with pin 9 tied to COMMON. Note 7: Error vs. crest factor is specified as an additional error for 200mVRMS rectangular pulse input, pulse width = 200s. Note 8: Input voltages are expressed in volts RMS. Note 9: With 10k external pull-down resistor from pin 6 (BUF OUT) to -VS. Note 10: With BUF input tied to COMMON.
_______________Detailed Description
The MX536A/MX636 uses an implicit method of RMS computation that overcomes the dynamic range as well as other limitations inherent in a straightforward computation of the RMS. The actual computation performed by the MX536A/MX636 follows the equation: VRMS = Avg. [VIN2/VRMS] The input voltage, VIN, applied to the MX536A/MX636 is processed by an absolute-value/voltage to current converter that produces a unipolar current I1 (Figure 1). This current drives one input of a squarer/divider that produces a current I4 that has a transfer function: I2 I4 = 1 I3 The current I4 drives the internal current mirror through a lowpass filter formed by R1 and an external capacitor, CAV. As long as the time constant of this filter is greater than the longest period of the input signal, I4 is averaged. The current mirror returns a current, I3, to the square/divider to complete the circuit. The current I4 is then a function of the average of (I12/I4), which is equal to I1RMS. The current mirror also produces a 2 * I4 output current, IOUT, that can be used directly or converted to a voltage using resistor R2 and the internal buffer to provide a low-impedance voltage output. The transfer function for the MX536A/MX636 is: VOUT = 2 * R2 * IRMS = VIN
The dB output is obtained by the voltage at the emitter of Q3, which is proportional to the -log VIN. The emitter follower Q5 buffers and level shifts this voltage so that the dB output is zero when the externally set emitter current for Q5 approximates I3.
Standard Connection (Figure 2)
The standard RMS connection requires only one external component, C AV . In this configuration the MX536A/MX636 measures the RMS of the AC and DC levels present at the input, but shows an error for lowfrequency inputs as a function of the CAV filter capacitor. Figure 3 gives practical values of CAV for various values of averaging error over frequency for the standard RMS connections (no post filtering). If a 3F capacitor is chosen, the additional error at 100Hz will be 1%. If the DC error can be rejected, a capacitor should be connected in series with the input, as would typically be the case in single-supply operation. The input and output signal ranges are a function of the supply voltages. Refer to the electrical characteristics for guaranteed performance. The buffer amplifier can be used either for lowering the output impedance of the circuit, or for other applications such as buffering highimpedance input signals. The MX536A/MX636 can be used in current output mode by disconnecting the internal load resistor, RL, from ground. The current output is available at pin 8 (pin 10 on the "H" package) with a nominal scale of 40A/VRMS input for the MX536A and 100A/VRMS input for the MX636. The output is positive.
6
_______________________________________________________________________________________
True RMS-to-DC Converters MX536A/MX636
CURRENT MIRROR +VS 14 COM 10
MX536A
0.2mA F.S.
I3
R1 25k CAV 4 I4 IOUT 8
0.4mA F.S. R2 25k IREF dB OUT 5 RL 9
ABSOLUTE VALUE/ VOLTAGE-CURRENT CONVERTER I1 R4 50k VIN 1 A1 12k 12k A2 Q2 VIN R-1 Q1
A3
Q3
BUFF IN 7 Q4 Q5
BUFFER A4
BUFF OUT 6
R3 25k
ONE-QUADRANT SQUARER/DIVIDER
25k -VS 3
Figure 1. MX536A Simplified Schematic
CAV
10 VIN
1 2
ABSOLUTE VALUE SQUARER DIVIDER
14 13 12 11
+VS
1 BUF CURRENT MIRROR SQUARER DIVIDER ABSOLUTE VALUE
9 VOUT
-VS
3 4 5
MX536A MX636
+VS
2
8
CURRENT MIRROR
10 9
3
7
VOUT
6 7
BUF
VIN CAV
4
6 5 -VS
8
Figure 2. MX536A/MX636 Standard RMS Connection
_______________________________________________________________________________________ 7
True RMS-to-DC Converters MX536A/MX636
100 EXTERNAL AVERAGING CAP, CAV (F) 10 OUTPUT SETTLING TIME TO COMPLETE 99% OF STEP_ (seconds) CAV
VIN R1
10
1
1 2
-VS
ABSOLUTE VALUE SQUARER DIVIDER
14 13 12 11
+VS
3 4 5
1 0.65 1% 0.22 0.1 1 10 60 100 1k FREQUENCY (Hz) 0.1%
0.1
CURRENT MIRROR
10 9
+VS R2
VOUT 0.01
6 7
BUF
8
R3
R4
Figure 3. Lower Frequency for Stated % of Reading Error and Settling Time for Circuit shown in Figure 2
High-Accuracy Adjustments
The accuracy of the MX536A/MX636 can be improved by the addition of external trims as shown in Figure 4. R4 trims the offset. The input should be grounded and R4 adjusted to give zero volts output from pin 6. R1 is trimmed to give the correct value for either a calibrated DC input or a calibrated AC signal. For example: 200mV DC input should give 200mV DC output; a 200mV peak-to-peak sine-wave should give 141mV DC output.
MX536A MX636
R1 R2 R3 R4
MX536A 500 365 750k 50k
MX636 200 154 470k 500k
-VS
Figure 4. Optional External Gain and Output Offset Trims
CAV
C2 VIN
Single-Supply Operation
Both the MX536A and the MX636 can be used with a single supply down to +5V (Figure 5). The major limitation of this connection is that only AC signals can be measured, since the differential input stage must be biased off ground for proper operation. The load resistor is necessary to provide output sink current. The input signal is coupled through C2 and the value chosen so that the desired low-frequency break point is obtained with the input resistance of 16.7k for the MX536A and 6.7k for the MX636. Figure 5 shows how to bias pin 10 within the range of the supply voltage (pin 2 on "H" packages). It is critical that no extraneous signals are coupled into this pin. A capacitor connected between pin 10 and ground is recommended. The common pin requires less than 5A of input current, and if the current flowing through resistors R1 and R2 is chosen to be approximately 10 times the common pin current, or 50A, the resistor values can easily be calculated.
1 2 3 4 5
+VS ABSOLUTE VALUE SQUARER DIVIDER
14 13 12 11
0.1F R1
CURRENT MIRROR
10 9
0.1F R2
VOUT RL 10k TO 1k
6 7
BUF
8
MX536A MX636
R1 R2 C2
MX536A 20k 10k 1F
MX636 20k 39k 3.3F
Figure 5. Single-Supply Operation
Choosing the Averaging Time Constant
Both the MX536A and MX636 compute the RMS value of AC and DC signals. At low frequencies and DC, the output tracks the input exactly; at higher frequencies,
8
the average output approaches the RMS value of the input signal. The actual output differs from the ideal by an average (or DC) error plus some amount of ripple. The DC error term is a function of the value of CAV and the input signal frequency. The output ripple is inverse-
_______________________________________________________________________________________
True RMS-to-DC Converters MX536A/MX636
MX536A
10 SETTLING TIME RELATIVE TO 200mVRMS INPUT SETTLING TIME SETTLING TIME RELATIVE TO 1VRMS INPUT SETTLING TIME 10
MX636
7.5
7.5
5
5
2.5 1 0 1m 10m 100m 1 10 RMS INPUT LEVEL (V)
2.5 1 0 1m 10m 100m 1 RMS INPUT LEVEL (V)
Figure 6a. MX536A Settling Time vs. Input Level
Figure 6b. MX636 Settling Time vs. Input Level
ly proportional to the value of CAV. Waveforms with high crest factors, such as a pulse train with low duty cycle, should have an average time constant chosen to be at least ten times the signal period. Using a large value of CAV to remove the output ripple increases the settling time for a step change in the input signal level. Figure 3 shows the relationship between CAV and settling time, where 115ms settling equals 1F of CAV. The settling time, or time for the RMS converter to settle to within a given percent of the change in RMS level, is set by the averaging time constant, which varies approximately 2:1 between increasing and decreasing input signals. For example, increasing input signals require 2.3 time constants to settle to within 1%, and 4.6 time constants for decreasing signals levels. In addition, the settling time also varies with input signal levels, increasing as the input signal is reduced, and decreasing as the input is increased as shown in Figures 6a and 6b.
Table 1. Number of RC Time Constants () Required for MX536A/MX636 RMS Converters to Settle to Within Stated % of Final Value
PARAMETERS FOR INCREASING AMPLITUDES FOR DECREASING AMPLITUDES
Basic Formulas Settling Time to Within Stated % of New RMS Level 1% 0.1% 0.01%
V 1 - e -T/RC
4.6/2.0 6.9/3.1 9.2/4.2
V
e -T/RC
4.6/4.6 6.9/6.9 9.2/9.2
Note: () Settling Times for Linear RC Filter
Decibel Output (dB)
The dB output of the MX536A/MX636 originates in the squarer/divider section and works well over a 60dB range. The connection for dB measurements is shown in Figure 10. The dB output has a temperature drift of 0.03dB/C, and in some applications may need to be compensated. Figure 10 shows a compensation scheme. The amplifier can be used to scale the output for a particular application. The values used in Figure 10 give an output of +100mV/dB.
Using Post Filters
A post filter allows a smaller value of CAV, and reduces ripple and improves the overall settling time. The value of CAV should be just large enough to give the maximum DC error at the lowest frequency of interest. The post filter is used to remove excess output ripple. Figures 7, 8, and 9 give recommended filter connections and values for both the MX536A and MX636. Table 1 lists the number of time constants required for the RMS section to settle to within different percentages of the final value for a step change in the input signal.
_______________________________________________________________________________________
9
True RMS-to-DC Converters MX536A/MX636
VIN
1
N.C. 2 CAV -VS
ABSOLUTE VALUE SQUARER DIVIDER
14 +VS 13 N.C. 12 N.C. 11 N.C.
COMMON RL IOUT
VIN
1 2
ABSOLUTE VALUE SQUARER DIVIDER
14 13 12 11
+VS
3 4
-VS
3 4
CAV
+VS
MX536A MX636
dB 5 VRMS OUT
CURRENT MIRROR
10 9
5 6 7
BUF
CURRENT MIRROR
10 9 8
6 7
BUF
8
C2 C2
RX*
C3 VRMS OUT
MX536A MX636
* MX536A = 25k MX636 = 10k
Figure 7. MX536A/MX636 with a One-Pole Output Filter
Figure 8. MX536A/MX636 with a Two-Pole Output Filter
Frequency Response
EDC ERROR OR RIPPLE (% OF READING) PK-PK RIPPLE PK-PK RIPPLE (ONE POLE) C2 = 4.7F 1 DC ERROR (ALL FILTERS) PK-PK RIPPLE (TWO POLE) C2 = C3 = 4.7F 0.1 10 100 1k 10k FREQUENCY (Hz) MX536A ONE-POLE FILTER C2 2.2F CAV 1F TWO-POLE FILTER 2.2F C2 2.2F C3 1F CAF MX636 4.7F 1F 4.7F 4.7F 1F RX = 0
10
The MX536A/MX636 utilizes a logarithmic circuit in performing the RMS computation of the input signal. The bandwidth of the RMS converters is proportional to signal level. Figures 11 and 12 represent the frequency response of the converters from 10mV to 7VRMS for the MX536A and 1mV to 1V for the MX636, respectively. The dashed lines indicate the upper frequency limits for 1%, 10%, and 3dB of reading additional error. Caution must be used when designing RMS measuring systems so that overload does not occur. The input clipping level for the MX636 is 12V, and for the MX536A it is 20V. A 7VRMS signal with a crest factor of 3 has a peak input of 21V.
Application in a Low-Cost DVM
A low-cost digital voltmeter (DVM) using just two integrated circuits plus supporting circuitry and LCD display is shown in Figure 13. The MAX130 is a 3 1/2 digit integrating A/D converter with precision bandgap reference. The 10M input attenuator is AC coupled to pin 6 of the MX636 buffer amplifier. The output from the MX636 is connected to the MAX130 to give a direct reading to the LCD display.
Figure 9. Performance Features of Various Filter Types for MX536A/MX636
10 ______________________________________________________________________________________
True RMS-to-DC Converters MX536A/MX636
MX536A MX636
VIN
1 2
ABSOLUTE VALUE SQUARER DIVIDER
14 13 12 11
+VS
VIN
+VS 4.5V TO 15V
R4 36k
-VS +VS C2 dB OUT -3mV/dB
C1 0.1F
3 4 5 6 7
BUF
VOUT 2.5V R1
MX580J
MAX400
GROUND R3 1k*
COMPENSATED dB OUT +0.1V/dB
CURRENT MIRROR
10 9 8
ZERO dB
LINEAR RMS OUTPUT
R5
R2 500 GAIN
*SPECIAL TC COMP RESISTOR: +3500PPM, 1k, 1%
Figure 10. dB Connection
10 7VRMS INPUT VOUT (V) 1 1VRMS INPUT 1% 10% 3dB VOUT (V)
1 200m 100m 30m 10m
1VRMS INPUT 200mVRMS INPUT 100mVRMS INPUT 30mVRMS INPUT 10mVRMS INPUT 1VRMS INPUT 1% 10% 3dB
0.1
100mVRMS INPUT 10mVRMS INPUT 1k 10k 100k FREQUENCY (Hz) 1M 10M
0.01
1m
100 1k 10k 100k FREQUENCY (Hz) 1M 10M
Figure 11. MX536A High-Frequency Response
Figure 12. MX636 High-Frequency Response
______________________________________________________________________________________
11
True RMS-to-DC Converters MX536A/MX636
VIN R1 9M 2V R2 900k 20V R3 90k 200V R5 47k 1W 10% 200mV D1 IN4148 C3 0.02F R6 1M C4 2.2F
1 2 3
6.8F
+VS ABSOLUTE VALUE SQUARER DIVIDER
14 13 12 11
R9 500k 0dB SET R11 26k
D3 D4 D5 R12 1k R13 500
+VDD ADC
V+ 9V BATTERY
1N4148 LIN
312 DIGIT
MAX130
REF HI VREF LO COM IN HI
4 5 6 7
BUF CURRENT MIRROR
dB R14 50k dB SCALE C6 0.01F IN LO
10 9 8
C7 6.8F
R10 20k
10k
LIN dB
LIN SCALE R15 1M
R4 10k COM
10k
D2 IN4148
R7 20k
MX636
LIN dB
312 DIGIT LCD DISPLAY
Figure 13. Portable High-Z Input RMS DPM and dB Meter
Typical Operating ________________Circuits (continued)
10 1 CURRENT MIRROR SQUARER DIVIDER ABSOLUTE VALUE 6 5 -VS BUF 8 9 VOUT
Pin Configurations (continued)
TOP VIEW
VIN 1 N.C. 2 -VS 3 CAV 4 dB 5 16 +VS 15 N.C. 14 N.C.
2
MX536A MX636
13 N.C. 12 COMMON 11 RL 10 IOUT 9 N.C.
+VS
3
7
BUF OUT 6 BUF IN 7 N.C. 8
VIN CAV
4
SO
___________________________________________Ordering Information (continued)
PART MX536ASH MX536ASQ* MX636JC/D MX636JCWE MX636JD MX636JH MX636JN TEMP. RANGE -55C to +125C -55C to +125C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C PIN-PACKAGE 10 TO-100 14 CERDIP Dice** 16 Wide SO 14 Ceramic 10 TO-100 14 Plastic DIP PART MX636JQ* MX636KCWE MX636KD MX636KH MX636KN MX636KQ* TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C PIN-PACKAGE 14 CERDIP 16 Wide SO 14 Ceramic 10 TO-100 14 Plastic DIP 14 CERDIP
* Maxim reserves the right to ship ceramic packages in lieu of CERDIP packages. ** Dice are specified at TA = +25C.
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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