MX536AJQ Просмотр технического описания (PDF) - Maxim Integrated
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MX536AJQ Datasheet PDF : 12 Pages
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True RMS-to-DC Converters
VIN
1
N.C. 2
CAV -VS 3
+VS
4
VRMS OUT
dB 5
6
7
ABSOLUTE
VALUE
SQUARER
DIVIDER
CURRENT
MIRROR
BUF
14 +VS
13 N.C.
12 N.C.
11 N.C.
COMMON
10
RL
9
8 IOUT
C2
MX536A
MX636
Figure 7. MX536A/MX636 with a One-Pole Output Filter
VIN
-VS
CAV
1
ABSOLUTE
VALUE
2
3
SQUARER
DIVIDER
4
5
CURRENT
MIRROR
6
7 BUF
14 +VS
13
12
MX536A
11
MX636
10
9
8
C2
RX*
* MX536A = 25kΩ
MX636 = 10kΩ
C3
VRMS OUT
Figure 8. MX536A/MX636 with a Two-Pole Output Filter
10
1
0.1
10
PK-PK RIPPLE
RX = 0
PK-PK RIPPLE
(ONE POLE)
C2 = 4.7µF
DC ERROR
(ALL FILTERS)
PK-PK RIPPLE
(TWO POLE)
C2 = C3 = 4.7µF
100
1k
10k
FREQUENCY (Hz)
MX536A
ONE-POLE FILTER
C2 2.2µF
CAV 1µF
TWO-POLE FILTER
C2 2.2µF
C3 2.2µF
CAF 1µF
MX636
4.7µF
1µF
4.7µF
4.7µF
1µF
Frequency Response
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
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 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.
Figure 9. Performance Features of Various Filter Types for
MX536A/MX636
10 ______________________________________________________________________________________
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