LM13700M National Semiconductor, LM13700M Datasheet - Page 20

• Manufacturer Part Number: LM13700M
• Description: Operational Amplifier (Op-Amp) IC
• Manufacturer: National Semiconductor

Specifications of LM13700M

• No. Of Amplifiers: 2
• No. Of Pins: 16
• Peak Reflow Compatible (260 C): No
• Leaded Process Compatible: No
• Mounting Type: Surface Mount
• Package / Case: 16-NSOIC
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Additional Applications
The Ramp-and-Hold of Figure 26 sources I
whenever the input to A1 is brought high, giving a ramp-rate
of about 1V/ms for the component values shown.
The true-RMS converter of Figure 27 is essentially an auto-
matic gain control amplifier which adjusts its gain such that
the AC power at the output of amplifier A1 is constant. The
output power of amplifier A1 is monitored by squaring ampli-
fier A2 and the average compared to a reference voltage
with amplifier A3. The output of A3 provides bias current to
FIGURE 24. Peak Detector and Hold Circuit
(Continued)
B
into capacitor C
FIGURE 23. Tachometer
20
the diodes of A1 to attenuate the input signal. Because the
output power of A1 is held constant, the RMS value is
constant and the attenuation is directly proportional to the
RMS value of the input voltage. The attenuation is also
proportional to the diode bias current. Amplifier A4 adjusts
the ratio of currents through the diodes to be equal and
therefore the voltage at the output of A4 is proportional to the
RMS value of the input voltage. The calibration potentiom-
eter is set such that V
O
reads directly in RMS volts.
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