MX536ASQ-883B Maxim Integrated Products, Inc., MX536ASQ-883B Datasheet - Page 10

• Manufacturer Part Number: MX536ASQ-883B
• Description: Mx536a, Mx636 True Rms-to-dc Converters
• Manufacturer: Maxim Integrated Products, Inc.

ly proportional to the value of C
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
increases the settling time for a step change in the input
signal level. Figure 3 shows the relationship between
C
of C
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.
A post filter allows a smaller value of C
ripple and improves the overall settling time. The value
of C
mum 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 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.
Figure 6a. MX536A Settling Time vs. Input Level
AV
AV
AV
and settling time, where 115ms settling equals 1µF
. The settling time, or time for the RMS converter to
should be just large enough to give the maxi-
2.5
10
7.5
5
1
0
1m
_______________________________________________________________________________________
10m
RMS INPUT LEVEL (V)
AV
MX536A
to remove the output ripple
100m
AV
Using Post Filters
. Waveforms with high
1
AV
, and reduces
10
True RMS-to-DC Converters
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.
Figure 6b. MX636 Settling Time vs. Input Level
Table 1. Number of RC Time Constants
( ) Required for MX536A/MX636 RMS
Converters to Settle to Within Stated % of
Final Value
Note: ( ) Settling Times for Linear RC Filter
Basic Formulas
Settling Time
to Within
Stated % of
New RMS
Level
PARAMETERS
2.5
10
7.5
5
1
0
1m
0.01%
0.1%
1%
RMS INPUT LEVEL (V)
10m
AMPLITUDES
INCREASING
V 1 - e
4.6 /2.0
6.9 /3.1
9.2 /4.2
MX636
FOR
Decibel Output (dB)
100m
-T/RC
DECREASING
AMPLITUDES
V
4.6 /4.6
6.9 /6.9
9.2 /9.2
1
FOR
e
-T/RC
9