AD736BR Analog Devices Inc, AD736BR Datasheet - Page 12

• Manufacturer Part Number: AD736BR
• Description: IC TRUE RMS/DC CONV LP 8-SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD736BR

• Rohs Status: RoHS non-compliant
• Current - Supply: 160µA
• Voltage - Supply: ±5.0V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• For Use With: AD736-EVALZ - BOARD EVALUATION FOR AD736

AD736
RAPID SETTLING TIMES VIA THE AVERAGE
RESPONDING CONNECTION
Because the average responding connection shown in Figure 19
does not use the C
not vary with the input signal level. It is determined solely by
the RC time constant of C
output amplifier’s feedback path.
DC ERROR, OUTPUT RIPPLE, AND AVERAGING
ERROR
Figure 20 shows the typical output waveform of the AD736
with a sine wave input applied. As with all real-world devices,
the ideal output of V
the output contains both a dc and an ac error component.
As shown in Figure 20, the dc error is the difference between
the average of the output signal (when all the ripple in the
output is removed by external filtering) and the ideal dc output.
The dc error component is therefore set solely by the value of
the averaging capacitor used. No amount of post filtering (that
is, using a very large C
ideal value. The ac error component, an output ripple, can be
easily removed by using a large enough post filtering capacitor, C
V
–V
IN
C
C
S
V
–V
C
IN
F
S
1
2
3
4
NEGATIVE SUPPLY
8kΩ
POSITIVE SUPPLY
SECTION
Figure 19. AD736 Average Responding Circuit
BIAS
AMPLIFIER
INPUT
COMMON
AV
OUT
averaging capacitor, its settling time does
F
) allows the output voltage to equal its
RECTIFIER
= V
CORE
rms
F
WAVE
10µF
33µF
+
FULL
C
C
and the internal 8 kΩ resistor in the
C
F
IN
+
(OPTIONAL)
is never achieved exactly. Instead,
0.1µF
0.1µF
AD736
AMPLIFIER
8kΩ
OUTPUT
+V
–V
S
S
8
7
6
5
OUTPUT
+V
C
S
AV
COM
+V
S
V
OUT
Rev. H | Page 12 of 20
F
.
In most cases, the combined magnitudes of both the dc and
ac error components need to be considered when selecting
appropriate values for Capacitor C
combined error, representing the maximum uncertainty of the
measurement, is termed the averaging error and is equal to the
peak value of the output ripple plus the dc error.
As the input frequency increases, both error components
decrease rapidly; if the input frequency doubles, the dc error
and ripple reduce to one quarter and one half of their original
values, respectively, and rapidly become insignificant.
AC MEASUREMENT ACCURACY AND CREST FACTOR
The crest factor of the input waveform is often overlooked when
determining the accuracy of an ac measurement. Crest factor is
defined as the ratio of the peak signal amplitude to the rms
amplitude (crest factor = V
such as sine and triangle waves, have relatively low crest factors
(≤2). Other waveforms, such as low duty-cycle pulse trains and
SCR waveforms, have high crest factors. These types of waveforms
require a long averaging time constant (to average out the long
periods between pulses). Figure 8 shows the additional error vs.
the crest factor of the AD736 for various values of C
Figure 20. Output Waveform for Sine Wave Input Voltage
E
O
DOUBLE-FREQUENCY
IDEAL
E
O
RIPPLE
PEAK
DC ERROR = E
/V rms). Many common waveforms,
AV
and Capacitor C
AVERAGE E
O
– E
O
(IDEAL)
O
= E
TIME
O
AV
F
.
. This