MX536ASQ-883B Maxim Integrated Products, Inc., MX536ASQ-883B Datasheet - Page 7

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

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:
The input voltage, V
processed by an absolute-value/voltage to current con-
verter that produces a unipolar current I
This current drives one input of a squarer/divider that
produces a current I
The current I
a lowpass filter formed by R1 and an external capaci-
tor, C
greater than the longest period of the input signal, I
averaged. The current mirror returns a current, I
square/divider to complete the circuit. The current I
then a function of the average of (I
to I
The current mirror also produces a 2 · I
I
age using resistor R2 and the internal buffer to provide
a low-impedance voltage output. The transfer function
for the MX536A/MX636 is:
True RMS-to-DC Converters
ELECTRICAL CHARACTERISTICS—MX636 (continued)
(T
Note 1: Accuracy is specified for 0 to 7V
Note 2: Error vs. crest factor is specified as an additional error for 1V
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
Note 7: Error vs. crest factor is specified as an additional error for 200mV
Note 8: Input voltages are expressed in volts RMS.
Note 9: With 10kΩ external pull-down resistor from pin 6 (BUF OUT) to -V
Note 10: With BUF input tied to COMMON.
6
_______________Detailed Description
OUT
POWER SUPPLY
Rated Performance
Dual Supplies
Single Supply
Quiescent Current (Note 10)
A
1RMS
= +25°C, +V
_______________________________________________________________________________________
, that can be used directly or converted to a volt-
AV
.
. As long as the time constant of this filter is
PARAMETER
4
S
V
drives the internal current mirror through
V
OUT
= +3V, -V
RMS
IN
4
= 2 · R2 · I
= Avg. [V
, applied to the MX536A/MX636 is
that has a transfer function:
I
S
4
= -5V, unless otherwise noted.)
= I
1
I
3
2
IN 2
RMS
/V
1 2
RMS
= V
RMS
/I
4
OUT
IN
), which is equal
4
]
, DC or 1kHz sine-wave input with the MX536A connected as in Figure 2.
output current,
), with pin 9 tied to COMMON.
1
(Figure 1).
CONDITIONS
3
, to the
4
4
is
is
The dB output is obtained by the voltage at the emitter
of Q3, which is proportional to the -log V
follower Q5 buffers and level shifts this voltage so that
the dB output is zero when the externally set emitter
current for Q5 approximates I
The standard RMS connection requires only one exter-
nal component, C
MX536A/MX636 measures the RMS of the AC and DC
levels present at the input, but shows an error for low-
frequency inputs as a function of the C
tor. Figure 3 gives practical values of C
values of averaging error over frequency for the stan-
dard RMS connections (no post filtering). 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.
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-
nal load resistor, R
available at pin 8 (pin 10 on the “H” package) with a
nominal scale of 40µA/V
100µA/V
RMS
S
RMS
rectangular pulse stream, pulse width = 200µs.
.
RMS
rectangular pulse input, pulse width = 200µs.
input for the MX636. The output is positive.
+2/-2.5
MIN
+5
L
, from ground. The current output is
AV
. In this configuration the
RMS
+3/-5
TYP
0.8
Standard Connection
3
input for the MX536A and
.
±16.5
MAX
+24
1
AV
IN
AV
. The emitter
filter capaci-
(Figure 2)
for various
UNITS
mA
V
V
V