MX536AJCWE [MAXIM]
True RMS-to-DC Converters; 真RMS - DC转换器
| 型号： | MX536AJCWE |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | True RMS-to-DC Converters |
| 文件： | 总12页 (文件大小：125K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-0824; Rev 2; 3/96
Tru e RMS -t o -DC Co n ve rt e rs
5A/MX36
Ge n e ra l De s c rip t io n
The MX536A and MX636 are true RMS-to-DC convert-
ers. They feature low power and are designed to accept
____________________________Fe a t u re s
♦ True RMS-to-DC Conversion
♦ Computes RMS of AC and DC Signals
low-level input signals from 0 to 7V
for the MX536A
RMS
♦ Wide Response:
and 0 to 200mV
for the MX636. Both devices accept
RMS
2MHz Bandwidth for V
1MHz Bandwidth for V
> 1V (MX536A)
> 100mV (MX636)
RMS
RMS
complex input waveforms containing AC and DC com-
ponents. They can be operated from either a single sup-
ply or dual supplies. Both devices draw less than 1mA
of quiescent supply current, making them ideal for bat-
tery-powered applications.
♦ Auxiliary dB Output: 60dB Range (MX536A)
50dB Range (MX636)
♦ Single- or Dual-Supply Operation
♦ Low Power: 1.2mA typ (MX536A)
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.
800µA typ (MX636)
Ord e rin g In fo rm a t io n
PART
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-55°C to +125°C
PIN-PACKAGE
Dice**
MX536AJC/D
MX536AJCWE
MX536AJD
MX536AJH
MX536AJN
MX536AJQ*
MX536AKCWE
MX536AKD
MX536AKH
MX536AKN
MX536AKQ*
MX536ASD
________________________Ap p lic a t io n s
Digital Multimeters
16 Wide SO
14 Ceramic
10 TO-100
Battery-Powered Instruments
Panel Meters
14 Plastic DIP
14 CERDIP
16 Wide SO
14 Ceramic
10 TO-100
Process Control
P in Co n fig u ra t io n s
14 Plastic DIP
14 CERDIP
14 Ceramic
TOP VIEW
I
OUT
10
R
BUF IN
9
6
L
1
4
Ordering Information continued at end of data sheet.
* Maxim reserves the right to ship ceramic packages in lieu of
CERDIP packages.
BUF OUT
8
7
COMMON 2
3
MX536A
MX636B
** Dice are specified at T = +25°C.
A
+V
S
dB
C
AV
V
IN
_________Typ ic a l Op e ra t in g Circ u it s
5
-V
S
C
AV
TO-100
V
+V
V
IN
1
+V
S
IN
S
14
13
12
11
10
9
1
2
3
4
5
6
7
ABSOLUTE
VALUE
14
13
12
11
10
9
N.C.
N.C.
2
3
4
5
6
7
-V
S
N.C.
-V
S
SQUARER
DIVIDER
C
AV
N.C.
MX536A
MX636
dB
BUF OUT
BUF IN
COMMON
CURRENT
MIRROR
R
L
V
OUT
8
I
OUT
BUF
8
DIP
Pin Configurations continued at end of data sheet.
Typical Operating Circuits continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.
Tru e RMS -t o -DC Co n ve rt e rs
ABSOLUTE MAXIMUM RATINGS
Supply Voltage: Dual Supplies (MX536A)............................±18V
(MX636) .............................±12V
Output Short-Circuit Duration ........................................Indefinite
Operating Temperature Ranges
Single Supply (MX536A)...........................+36V
(MX636) .............................+24V
Input Voltage (MX536A).......................................................±25V
(MX636).........................................................±12V
Power Dissipation (Package)
Commercial (J, K) ...............................................0°C to +70°C
Military (S)......................................................-55°C to +125°C
Storage Temperature Range .............................-55°C to +150°C
Lead Temperature (soldering, 10sec)................................300°C
Plastic DIP (derate 12mW/°C above +75°C) ...............450mW
Small Outline (derate 10mW/°C above +75°C)............400mW
Ceramic (derate 10mW/°C above +75°C) ...................500mW
TO-100 metal can (derate 7mW/°C above +75°C) ......450mW
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.
5A/MX36
ELECTRICAL CHARACTERISTICS—MX536A
(T = +25°C, +V = +15V, -V = -15V, unless otherwise noted.)
A
S
S
PARAMETER
CONDITIONS
MIN
TYP
= [avg. (V )2] 1/
IN
MAX
UNITS
ms/µF C
Transfer Equation
V
OUT
2
Averaging Time Constant
Figure 3
25
AV
CONVERSION ACCURACY
MX536AJ, AS
MX536AK
±5 ±0.5
±2 ±0.2
mV ±% of
Reading
Total Error, Internal Trim (Note 1)
MX536AJ
MX536AK
MX536AS
MX536AS
±0.1 ±0.01
±0.05 ±0.005
±0.1 ±0.005
±0.03 ±0.005
T
to +70°C
MIN
mV ±% of
Reading/°C
Total Error vs. Temperature
+70°C to +125°C
mV ±% of
Reading/V
Total Error vs. Supply
±0.1 ±0.01
MX536AJ, AS
MX536AK
±0.2
±0.1
% of
Reading
Total Error vs. DC Reversal
MX536AJ, AS
MX536AK
±3 ±0.3
±2 ±0.1
Total Error, External Trim
(Note 1)
mV ±% of
Reading
ERROR vs. CREST FACTOR (Note 2)
Crest Factor 1 to 2
Specified Accuracy
% of
Reading
Additional Error
Crest Factor = 3
Crest Factor = 7
-0.1
-1.0
FREQUENCY RESPONSE (Note 3)
V
= 10mV
= 100mV
= 1V
5
IN
Bandwidth for 1%
Additional Error (0.09dB)
V
IN
45
kHz
V
IN
120
90
V
IN
= 10mV
= 100mV
= 1V
kHz
±3dB Bandwidth
V
IN
450
2.3
V
IN
MHz
2
_______________________________________________________________________________________
Tru e RMS -t o -DC Co n ve rt e rs
5A/MX36
ELECTRICAL CHARACTERISTICS—MX536A (continued)
(T = +25°C, +V = +15V, -V = -15V, unless otherwise noted.)
A
S
S
PARAMETER
CONDITIONS
MIN
TYP
0 to 7
0 to 2
MAX
UNITS
INPUT CHARACTERISTICS
V
RMS
±15V Supplies
Continuous RMS Peak Transient
±20
V
PK
Input Signal Range
V
RMS
±5V Supplies
Continuous RMS Peak Transient
±7
±25
20.00
±2
V
PK
Safe Input
All Supplies
V
PK
Input Resistance
13.33
16.7
0.8
kΩ
MX536AJ, AS
MX536AK
Input Offset Voltage
mV
0.5
±1
OUTPUT CHARACTERISTICS
MX536AJ
±1
±2
±1
±2
T
A
= +25°C
MX536AK
±0.5
mV
MX536AS
Offset Voltage
MX536AJ, AK
MX536AS
±0.1
T
= T
to T
MAX
mV/°C
mV/V
V
A
MIN
±0.2
MX536AJ, AK
MX536AS
±0.1
±0.2
12.5
Supply Voltage
±15V Supplies
±5V Supplies
Source
0 to 11
0 to 2
5
Output Voltage Swing
Output Current
mA
µA
mA
Ω
Sink
-130
Short Circuit Current
Output Resistance
dB OUTPUT
20
0.5
MX536AJ
MX536AK
MX536AS
±0.4
±0.2
±0.5
-3
±0.6
±0.3
±0.6
V
= 7mV to 7V
,
IN
RMS
Error
dB
0dB = 1V
RMS
Scale Factor
mV/dB
% of
Reading/°C
Scale Factor TC (Uncompensated)
0.33
20
I
0dB = 1V
5
1
80
µA
µA
RMS
REF
I
Range
100
REF
I
TERMINAL
OUT
I
Scale Factor
Scale Factor Tolerance
40
±10
25
µA/V
RMS
OUT
I
±20
30
%
OUT
Output Resistance
20
kΩ
-V to
S
Voltage Compliance
V
(+V - 2.5)
S
_______________________________________________________________________________________
3
Tru e RMS -t o -DC Co n ve rt e rs
ELECTRICAL CHARACTERISTICS—MX536A (continued)
(T = +25°C, +V = +15V, -V = -15V, unless otherwise noted.)
A
S
S
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
BUFFER AMPLIFIER
-V to
(+V - 2.5)
S
S
Input and Output Voltage Range
V
Input Offset Voltage
Input Bias Current
Input Resistance
R
= 25kΩ
±0.5
20
108
±4
mV
nA
S
300
Ω
Source
Sink
+5
mA
µA
Output Current
-130
Short-Circuit Current
Small-Signal Bandwidth
Slew Rate (Note 4)
20
1
mA
MHz
V/µs
5A/MX36
5
ELECTRICAL CHARACTERISTICS—MX636
(T = +25°C, +V = +3V, -V = -5V, unless otherwise noted.)
A
S
S
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Transfer Equation
V
OUT
= [avg. (V )2]1/2
IN
Averaging Time Constant
Figure 3
25
ms/µF C
AV
CONVERSION ACCURACY
MX636J
MX636K
MX636J
MX636K
±0.5 ±1.0
±0.2 ±0.5
Total Error, Internal Trim
(Notes 5, 6)
mV ±% of
Reading
±0.1 ±0.01
±0.1 ±0.005
Total Error vs. Temperature
(0°C to +70°C)
mV ±% of
Reading/°C
mV ±% of
Reading/V
Total Error vs. Supply
±0.1 ±0.01
MX636J
MX636K
±0.2
±0.1
±% of
Reading
Total Error vs. DC Reversal
V
IN
= 200mV
MX636J
MX636K
±0.3 ±0.1
±0.1 ±0.1
Total Error, External Trim
(Note 5)
mV ±% of
Reading
ERROR vs. CREST FACTOR (Note 3)
Crest Factor 1 to 2
Crest Factor = 3
Crest Factor = 6
FREQUENCY RESPONSE (Notes 6, 8)
Specified Accuracy
±% of
Reading
Additional Error
-0.2
-0.5
V
= 10mV
14
90
IN
Bandwidth for 1%
Additional Error (0.09dB)
V
IN
= 100mV
= 200mV
= 10mV
kHz
V
IN
130
100
900
1.5
V
IN
kHz
±3dB Bandwidth
V
IN
= 100mV
= 200mV
V
IN
MHz
4
_______________________________________________________________________________________
Tru e RMS -t o -DC Co n ve rt e rs
5A/MX36
ELECTRICAL CHARACTERISTICS—MX636 (continued)
(T = +25°C, +V = +3V, -V = -5V, unless otherwise noted.)
A
S
S
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
mV
INPUT CHARACTERISTICS
Continuous RMS, All Supplies
0 to 200
RMS
+3V, -5V Supplies
±2.8
±2
Input Signal Range
Peak Transient
All Supplies
±2.5V Supplies
±5V Supplies
V
PK
±5
Safe Input
±12
8.00
±0.5
±0.2
V
PK
Input Resistance
5.33
6.7
kΩ
MX636J
MX636K
Input Offset Voltage
mV
OUTPUT CHARACTERISTICS (Note 5)
MX636J
MX636K
±0.5
±0.2
T
= +25°C
mV
A
Offset Voltage
T
A
= T
to T
MAX
±10
µV/°C
mV/V
MIN
With Supply Voltage
+3V, -5V Supplies
±0.1
0 to 1
0 to 1
8
Output Voltage Swing
V
±5V to ±16.5V Supplies
1.4
10
Output Resistance
12
kΩ
dB OUTPUT
MX636J
MX636K
±0.3
±0.1
-3
±0.5
±0.2
Error
7mV ≤ V ≤ 300mV
dB
IN
Scale Factor
Scale Factor Tempco
mV/dB
%/°C
dB/°C
µA
+0.33
-0.033
4
I
0dB = 1V
2
1
8
RMS
REF
I
Range
50
µA
REF
I
TERMINAL
OUT
I
Scale Factor
Scale Factor Tolerance
100
±10
10
µA/V
RMS
OUT
I
-20
8
+20
12
%
OUT
Output Resistance
kΩ
-V to
(+V - 2.0)
S
S
Voltage Compliance
V
BUFFER AMPLIFIER
Input and Output Voltage Range
-V to
(+V - 2)
S
S
V
MX636J
MX636K
±0.8
±0.5
100
108
±2
±1
Input Offset Voltage
R
= 10kΩ
mV
S
Input Current
300
nA
Ω
Input Resistance
Source
Sink
+5
mA
µA
Output Current
-130
Short-Circuit Current
Small-Signal Bandwidth
Slew Rate (Note 9)
20
1
mA
MHz
V/µs
5
_______________________________________________________________________________________
5
Tru e RMS -t o -DC Co n ve rt e rs
ELECTRICAL CHARACTERISTICS—MX636 (continued)
(T = +25°C, +V = +3V, -V = -5V, unless otherwise noted.)
A
S
S
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
POWER SUPPLY
Rated Performance
Dual Supplies
+3/-5
V
V
+2/-2.5
+5
±16.5
+24
1
Single Supply
V
Quiescent Current (Note 10)
0.8
mA
Note 1: Accuracy is specified for 0 to 7V
, DC or 1kHz sine-wave input with the MX536A connected as in Figure 2.
RMS
Note 2: Error vs. crest factor is specified as an additional error for 1V
rectangular pulse stream, pulse width = 200µs.
RMS
Note 3: Input voltages are expressed in volts RMS, and error as % of reading.
Note 4: With 2kΩ 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 (I ), with pin 9 tied to COMMON.
OUT
5A/MX36
Note 7: Error vs. crest factor is specified as an additional error for 200mV
rectangular pulse input, pulse width = 200µs.
RMS
Note 8: Input voltages are expressed in volts RMS.
Note 9: With 10kΩ external pull-down resistor from pin 6 (BUF OUT) to -V .
S
Note 10: With BUF input tied to COMMON.
The dB output is obtained by the voltage at the emitter
of Q3, which is proportional to the -log V . The emitter
IN
follower Q5 buffers and level shifts this voltage so that
the dB output is zero when the externally set emitter
_______________De t a ile d De s c rip t io n
The MX536A/MX636 uses an implicit method of RMS
computation that overcomes the dynamic range as well
as other limitations inherent in a straightforward compu-
tation of the RMS. The actual computation performed
by the MX536A/MX636 follows the equation:
current for Q5 approximates I .
3
S t a n d a rd Co n n e c t io n
(Fig u re 2 )
The standard RMS connection requires only one exter-
2
V
RMS
= Avg. [V /V
]
IN
RMS
The input voltage, V , applied to the MX536A/MX636 is
IN
na l c omp one nt, C . In this c onfig ura tion the
AV
processed by an absolute-value/voltage to current con-
verter that produces a unipolar current I (Figure 1).
1
MX536A/MX636 measures the RMS of the AC and DC
levels present at the input, but shows an error for low-
This current drives one input of a squarer/divider that
frequency inputs as a function of the C
filter capaci-
AV
produces a current I that has a transfer function:
4
tor. Figure 3 gives practical values of C
for various
AV
2
I
1
I
3
values of averaging error over frequency for the stan-
d a rd RMS c onne c tions (no p os t filte ring ). If a 3µF
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.
I =
4
The current I drives the internal current mirror through
4
a lowpass filter formed by R1 and an external capaci-
tor, C . As long as the time constant of this filter is
AV
greater than the longest period of the input signal, I is
4
averaged. The current mirror returns a current, I , to the
3
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 cir-
cuit, or for other applications such as buffering high-
impedance input signals. The MX536A/MX636 can be
used in current output mode by disconnecting the inter-
square/divider to complete the circuit. The current I is
4
2
then a function of the average of (I /I ), which is equal
1
4
to I
.
RMS
1
The current mirror also produces a 2 · I output current,
4
I
, that can be used directly or converted to a volt-
OUT
age using resistor R2 and the internal buffer to provide
a low-impedance voltage output. The transfer function
for the MX536A/MX636 is:
nal load resistor, R , from ground. The current output is
L
available at pin 8 (pin 10 on the “H” package) with a
nominal scale of 40µA/V
input for the MX536A and
RMS
V
OUT
= 2 · R2 · I = V
RMS IN
100µA/V
input for the MX636. The output is positive.
RMS
6
_______________________________________________________________________________________
Tru e RMS -t o -DC Co n ve rt e rs
5A/MX36
CURRENT MIRROR
+V
S
14
COM
10
MX536A
0.4mA
F.S.
R1
25k
R2
R
L
0.2mA
F.S.
I
3
C
AV
I
OUT 8
9
4
25k
I
4
dB
ABSOLUTE VALUE/
VOLTAGE-CURRENT
CONVERTER
OUT
I
REF
A3
5
I
1
-1
V
IN
R
R4
Q1
Q2
50k
Q3
BUFF
IN
V
IN
BUFFER
A4
BUFF
OUT
1
7
A1
Q4
6
Q5
12k
A2
R3
25k
ONE-QUADRANT
SQUARER/DIVIDER
25k
12k
-V
S
3
Figure 1. MX536A Simplified Schematic
C
AV
10
V
+V
S
IN
9
1
2
3
4
5
6
7
ABSOLUTE
VALUE
1
14
13
12
11
10
9
BUF
V
OUT
CURRENT
MIRROR
8
7
2
MX536A
MX636
-V
SQUARER
DIVIDER
S
SQUARER
DIVIDER
+V
S
3
CURRENT
MIRROR
ABSOLUTE
VALUE
V
OUT
4
V
IN
6
BUF
8
5
C
AV
-V
S
Figure 2. MX536A/MX636 Standard RMS Connection
_______________________________________________________________________________________
7
Tru e RMS -t o -DC Co n ve rt e rs
C
AV
100
10
V
IN
+V
S
1
2
3
4
5
6
7
ABSOLUTE
VALUE
14
13
12
11
10
9
10
1
R1
-V
SQUARER
DIVIDER
S
1
0.1
0.65
+V
S
1%
CURRENT
MIRROR
0.1%
R2
R3
0.22
0.1
V
OUT
0.01
BUF
1
10
60 100
1k
8
R4
FREQUENCY (Hz)
5A/MX36
Figure 3. Lower Frequency for Stated % of Reading Error and
Settling Time for Circuit shown in Figure 2
-V
S
MX536A MX636
R1 500Ω
R2 365Ω
R3 750kΩ
R4 50kΩ
200Ω
154Ω
470kΩ
500kΩ
Hig h -Ac c u ra c y Ad ju s t m e n t s
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
Figure 4. Optional External Gain and Output Offset Trims
C
AV
C2
+V
S
V
IN
1
2
3
4
5
6
7
ABSOLUTE
VALUE
14
13
12
11
10
9
S in g le -S u p p ly Op e ra t io n
Both the MX536A and the MX636 can be used with a
single supply down to +5V (Figure 5). The major limita-
tion 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 resis-
tor is necessary to provide output sink current. The
input signal is coupled through C2 and the value cho-
sen so that the desired low-frequency break point is
obtained with the input resistance of 16.7kΩ for the
MX536A and 6.7kΩ for the MX636.
0.1µF
SQUARER
DIVIDER
R1
CURRENT
MIRROR
V
OUT
0.1µF
R2
BUF
8
R
L
10k TO 1k
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 5µA
of input current, and if the current flowing through resis-
tors R1 and R2 is chosen to be approximately 10 times
the common pin current, or 50µA, the resistor values
can easily be calculated.
MX536A MX636
R1 20kΩ
R2 10kΩ
20kΩ
39kΩ
3.3µF
MX536A
MX636
C2
1µF
Figure 5. Single-Supply Operation
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.
Ch o o s in g t h e Ave ra g in g Tim e Co n s t a n t
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,
The DC error term is a function of the value of C
the input signal frequency. The output ripple is inverse-
and
AV
8
_______________________________________________________________________________________
Tru e RMS -t o -DC Co n ve rt e rs
5A/MX36
MX536A
MX636
10
10
7.5
5
7.5
5
2.5
2.5
1
0
1
0
1m
10m
100m
1
10
1m
10m
100m
1
RMS INPUT LEVEL (V)
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 C . Waveforms with high
AV
Table 1. Number of RC Time Constants
(τ) Required for MX536A/MX636 RMS
Converters to Settle to Within Stated % of
Final Value
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 C
to remove the output ripple
AV
increases the settling time for a step change in the input
signal level. Figure 3 shows the relationship between
FOR
FOR
PARAMETERS
INCREASING
AMPLITUDES
DECREASING
AMPLITUDES
C
and settling time, where 115ms settling equals 1µF
AV
of C . The settling time, or time for the RMS converter to
AV
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.
Basic Formulas
-T/RC
-T/RC
∆V 1 - e
∆V
e
Settling Time
to Within
Stated % of
New RMS
Level
4.6τ/2.0τ
6.9τ/3.1τ
9.2τ/4.2τ
4.6τ/4.6τ
6.9τ/6.9τ
9.2τ/9.2τ
1%
0.1%
0.01%
In addition, the settling time also varies with input signal
levels, increasing as the input signal is reduced, and
d e c re a s ing a s the inp ut is inc re a s e d a s s hown in
Figures 6a and 6b.
Note: (τ) Settling Times for Linear RC Filter
De c ib e l Ou t p u t (d B)
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
c omp e ns a te d . Fig ure 10 s hows a c omp e ns a tion
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.
Us in g P o s t Filt e rs
A post filter allows a smaller value of C , and reduces
AV
ripple and improves the overall settling time. The value
of C
should be just large enough to give the maxi-
AV
mum DC error at the lowest frequency of interest. The
p os t filte r is us e d to re move e xc e s s outp ut rip p le .
Figures 7, 8, and 9 give recommended filter connec-
tions 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
Tru e RMS -t o -DC Co n ve rt e rs
V
IN
+V
S
1
2
3
4
5
6
7
ABSOLUTE
VALUE
14
13
12
11
10
9
V
+V
IN
S
1
2
3
4
5
6
7
ABSOLUTE
VALUE
14
13
12
11
10
9
N.C.
N.C.
N.C.
SQUARER
DIVIDER
-V
S
SQUARER
DIVIDER
-V
S
MX536A
MX636
C
AV
+V
S
N.C.
C
AV
CURRENT
MIRROR
COMMON
CURRENT
MIRROR
dB
R
L
V
RMS
OUT
BUF
8
I
OUT
BUF
8
C2
5A/MX36
C3
R *
X
C2
V
RMS
OUT
MX536A
MX636
* MX536A = 25kΩ
MX636 = 10kΩ
Figure 7. MX536A/MX636 with a One-Pole Output Filter
Figure 8. MX536A/MX636 with a Two-Pole Output Filter
Fre q u e n c y Re s p o n s e
The MX536A/MX636 utilizes a logarithmic circuit in per-
forming the RMS computation of the input signal. The
bandwidth of the RMS converters is proportional to sig-
nal level. Figures 11 and 12 represent the frequency
R = 0
X
PK-PK RIPPLE
PK-PK RIPPLE
10
1
response of the converters from 10mV to 7V
for the
RMS
(ONE POLE)
C2 = 4.7µF
MX536A and 1mV to 1V for the MX636, respectively.
The dashed lines indicate the upper frequency limits for
1%, 10%, a nd ± 3d B of re a d ing a d d itiona l e rror.
Caution must be used when designing RMS measuring
systems so that overload does not occur. The input
c lip p ing le ve l for the MX636 is ± 12V, a nd for the
DC ERROR
(ALL FILTERS)
PK-PK RIPPLE
(TWO POLE)
C2 = C3 = 4.7µF
MX536A it is ±20V. A 7V
signal with a crest factor
RMS
of 3 has a peak input of 21V.
0.1
10
100
1k
10k
Ap p lic a t io n in a Lo w -Co s t DVM
A low-cost digital voltmeter (DVM) using just two inte-
grated circuits plus supporting circuitry and LCD dis-
play is shown in Figure 13. The MAX130 is a 3 1/2 digit
integrating A/D converter with precision bandgap refer-
ence. The 10MΩ 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.
FREQUENCY (Hz)
MX536A
ONE-POLE FILTER
MX636
C2
2.2µF
1µF
4.7µF
1µF
C
AV
TWO-POLE FILTER
C2
C3
2.2µF
2.2µF
1µF
4.7µF
4.7µF
1µF
C
AF
Figure 9. Performance Features of Various Filter Types for
MX536A/MX636
10 ______________________________________________________________________________________
Tru e RMS -t o -DC Co n ve rt e rs
5A/MX36
MX536A
MX636
V
+V
4.5V TO 15V
IN
+V
S
S
R4
36k
V
IN
14
13
12
11
10
9
1
2
3
4
5
6
7
ABSOLUTE
VALUE
V
2.5V
OUT
SQUARER
DIVIDER
-V
S
C1
MX580J
COMPENSATED
dB OUT
+0.1V/dB
+V
S
MAX400
C2 0.1µF
R1
ZERO dB
CURRENT
MIRROR
R3
1k*
GROUND
dB OUT
-3mV/dB
BUF
8
LINEAR
RMS
R2
R5
OUTPUT
500Ω
GAIN
*SPECIAL TC COMP RESISTOR: +3500PPM, 1k, 1%
Figure 10. dB Connection
1V INPUT
RMS
10
1
200m
100m
1%
7V INPUT
RMS
10%
200mV INPUT
RMS
10%
1%
±3dB
100mV INPUT
RMS
1
±3dB
1V INPUT
RMS
30mV INPUT
RMS
30m
10m
10mV INPUT
RMS
0.1
100mV
RMS
INPUT
1V INPUT
RMS
0.01
1m
10mV
RMS
INPUT
100µ
1k
10k
100k
FREQUENCY (Hz)
1M
10M
1k
10k
100k
FREQUENCY (Hz)
1M
10M
Figure 11. MX536A High-Frequency Response
Figure 12. MX636 High-Frequency Response
______________________________________________________________________________________ 11
Tru e RMS -t o -DC Co n ve rt e rs
200mV
V
IN
D1
IN4148
C4
2.2µF
R1
+V
S
9M
C3
+V
DD
V+
1
2
3
4
5
6
7
ABSOLUTE
VALUE
0.02µF
14
13
12
11
10
9
D3
D4
D5
2V
R11
26k
1
1N4148
LIN
3 ⁄ DIGIT
2
R6
R9
ADC
MAX130
9V
BATTERY
1M
R2
900k
500k
0dB SET
SQUARER
DIVIDER
REF HI
R12
R5
47k
1W
10%
1k
dB
20V
V-
6.8µF
R14
50k
R10
20k
CURRENT
MIRROR
R3
90k
R13
500Ω
REF LO
COM
LIN
dB
10k
200V
LIN
BUF
SCALE SCALE
1
8
3 ⁄
2
10k
IN HI
dB
R4
10k
DIGIT
LCD
D2
R15
1M
X
C6
0.01µF
R7
20k
C7
6.8µF
IN4148
LIN
DISPLAY
MX636
IN LO
COM
dB
Figure 13. Portable High-Z Input RMS DPM and dB Meter
Typ ic a l Op e ra t in g
________________Circ u it s (c o n t in u e d )
P in Co n fig u ra t io n s (c o n t in u e d )
TOP VIEW
1
2
3
4
5
6
7
8
16
15
V
+V
S
10
IN
9
1
N.C.
-V
N.C.
14 N.C.
S
V
OUT
BUF
CURRENT
MIRROR
8
7
2
13
12
11
10
9
C
AV
MX536A
MX636
N.C.
dB
BUF OUT
BUF IN
N.C.
COMMON
SQUARER
DIVIDER
R
L
+V
S
3
I
OUT
N.C.
ABSOLUTE
VALUE
4
V
IN
6
C
AV
5
SO
-V
S
___________________________________________Ord e rin g In fo rm a t io n (c o n t in u e d )
PART
MX636JQ*
MX636KCWE
MX636KD
MX636KH
MX636KN
MX636KQ*
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
PIN-PACKAGE
14 CERDIP
PART
MX536ASH
MX536ASQ*
MX636JC/D
MX636JCWE
MX636JD
TEMP. RANGE
-55°C to +125°C
-55°C to +125°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
PIN-PACKAGE
10 TO-100
14 CERDIP
Dice**
16 Wide SO
14 Ceramic
10 TO-100
16 Wide SO
14 Ceramic
10 TO-100
14 Plastic DIP
14 Plastic DIP
14 CERDIP
MX636JH
MX636JN
* Maxim reserves the right to ship ceramic packages in lieu of CERDIP packages.
** Dice are specified at T = +25°C.
A
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 ____________________Ma x im In t e g ra t e d P ro d u c t s , 1 2 0 S a n Ga b rie l Drive , S u n n yva le , CA 9 4 0 8 6 4 0 8 -7 3 7 -7 6 0 0
© 1998 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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