AD737AQ Analog Devices Inc, AD737AQ Datasheet - Page 15

• Manufacturer Part Number: AD737AQ
• Description: IC AC RMS TO DC CONV 5V 8-CDIP
• Manufacturer: Analog Devices Inc

Specifications of AD737AQ

• Rohs Status: RoHS non-compliant
• Current - Supply: 170mA
• Voltage - Supply: ±5.0V
• Mounting Type: Through Hole
• Package / Case: 8-CDIP (0.300", 7.62mm)
• For Use With: AD737-EVALZ - BOARD EVALUATION FOR AD737

Battery Operation
All the level-shifting for battery operation is provided by the
3½ digit converter, shown in Figure 28. Alternatively, an
external op amp adds flexibility by accommodating nonzero
common-mode voltages and providing output scaling and
offset to zero. When an external operational amplifier is used,
the output polarity is positive going.
Figure 29 shows an op amp used in a single-supply application.
Note that the combined input resistor value (R1 + R2 + 8 kΩ)
matches that of the R5 feedback resistor. In this instance, the
magnitudes of the output dc voltage and the rms of the ac input
are equal. R3 and R4 provide current to offset the output to 0 V.
Scaling the Output Voltage
The output voltage can be scaled to the input rms voltage. For
example, assume that the AD737 is retrofitted to an existing
application using an averaging responding circuit (full-wave
rectifier). The power supply is 12 V, the input voltage is 10 V ac,
and the desired output is 6 V dc.
For convenience, use the same combined input resistance as
shown in Figure 29. Calculate the rms input current as
Table 6. AD737 Capacitor Selection
Application
General-Purpose RMS
General-Purpose Average
SCR Waveform
Audio Applications
1
Settling time is specified over the stated rms input level with the input signal increasing from zero. Settling times are greater for decreasing amplitude input signals.
Computation
Responding
Measurement
Speech
Music
I
INMAG
=
69.8
kΩ
+
10
2.5
V
kΩ
RMS Input Level
0 V to 1 V
0 mV to 200 mV
0 V to 1 V
0 mV to 200 mV
0 mV to 200 mV
0 mV to 100 mV
0 mV to 200 mV
0 mV to 100 mV
+
8
kΩ
=
125
μ
A
=
I
OUTMAG
Low Frequency
Cutoff (−3 dB)
20 Hz
200 Hz
20 Hz
200 Hz
20 Hz
200 Hz
20 Hz
200 Hz
50 Hz
60 Hz
50 Hz
60 Hz
300 Hz
20 Hz
Rev. H | Page 15 of 24
(2)
Next, using the I
feedback resistor required for 6 V output using
Select the closest-value standard 1% resistor, 47.5 kΩ.
Because the supply is 12 V, the common-mode voltage at the
R7/R8 divider is 6 V, and the combined resistor value
(R3 + R4) is equal to the feedback resistor, or 47.5 kΩ.
R2 is used to calibrate the transfer function (gain), and R4 sets
the output voltage to zero with no input voltage.
Perform calibration as follows:
1.
2.
3.
The op amp selected for any single-supply application must bea
rail-to-rail type, for example an AD8541, as shown in Figure 29.
For higher voltages, a higher voltage part, such as an OP196,
can be used. When calibrating to 0 V, the specified voltage
above ground for the operational amplifier must be taken into
account. Adjust R4 slightly higher as appropriate.
Maximum
Crest Factor
5
5
5
5
5
5
5
5
3
10
With no ac input applied, adjust R4 for 0 V.
Apply a known input to the input.
Adjust the R2 trimmer until the input and output match.
R
FB
=
125
6
V
μ
OUTMAG
A
C
15
3.3
None
None
82
47
150
33
None
None
100
50
1.5
100
AV
=
(μF)
48.1
value from Equation 2, calculate the
kΩ
C
10
1
10
1
33
3.3
33
3.3
33
27
33
27
0.5
68
F
(μF)
Settling Time
360 ms
36 ms
360 ms
36 ms
1.2 sec
120 ms
1.2 sec
120 ms
1.2 sec
1.0 sec
1.2 sec
1.0 sec
18 ms
2.4 sec
AD737
1
to 1%
(3)