MX536A 查看數據表（PDF） - Maxim Integrated
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MX536A Datasheet PDF : 12 Pages
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True RMS-to-DC Converters
100
10
CAV
10
1
1
0.65
0.22
0.1
1
0.1
1%
0.1%
10
60 100
FREQUENCY (Hz)
0.01
1k
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.
Single-Supply Operation
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.
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.
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,
VIN
R1
-VS
VOUT
1
ABSOLUTE
14
+VS
VALUE
2
13
3
SQUARER
DIVIDER
12
4
11
5
CURRENT
MIRROR
10
R2
+VS
6
9
7 BUF
8
R3 R4
MX536A MX636
-VS
R1 500Ω
200Ω
MX536A
MX636
R2 365Ω
R3 750kΩ
R4 50kΩ
154Ω
470kΩ
500kΩ
Figure 4. Optional External Gain and Output Offset Trims
CAV
C2
VIN
VOUT
RL
1
ABSOLUTE
VALUE
2
3
SQUARER
DIVIDER
4
5
CURRENT
MIRROR
6
7 BUF
+VS
14
0.1µF
13
12
R1
11
10
9
0.1µF
R2
8
10k TO 1k
MX536A
MX636
MX536A
R1 20kΩ
R2 10kΩ
C2 1µF
MX636
20kΩ
39kΩ
3.3µF
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.
The DC error term is a function of the value of CAV and
the input signal frequency. The output ripple is inverse-
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