LM13700N National Semiconductor, LM13700N Datasheet - Page 18

• Manufacturer Part Number: LM13700N
• Description: Operational Amplifier (Op-Amp) IC
• Manufacturer: National Semiconductor

Specifications of LM13700N

• No. Of Amplifiers: 2
• Slew Rate: 50V/µs
• No. Of Pins: 16
• Peak Reflow Compatible (260 C): No
• Input Bias Current: 1µA
• Supply Voltage: 36V
• Output Current: 20mA
• Input Offset Voltage Max: 4mV
• Gain: 2dB
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

www.national.com
Additional Applications
Figure 23 shows a Tachometer or Frequency-to-Voltage con-
verter. Whenever A1 is toggled by a positive-going input, an
amount of charge equal to (V
R
rent of V
time required to charge C
where V
high output voltage swing of the LM13700. D1 is added to
provide a discharge path for C
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
t
. This once per cycle charge is then balanced by the cur-
L
O
and V
/R
t
. The maximum F
H
represent the maximum low and maximum
t
from V
H
–V
IN
t
when A1 switches low.
L
is limited by the amount of
L
) C
to V
t
is sourced into C
H
FIGURE 24. Peak Detector and Hold Circuit
with a current of I
(Continued)
B
into capacitor C
FIGURE 23. Tachometer
f
and
B
,
18
The Peak Detector of Figure 24 uses A2 to turn on A1 when-
ever V
storage capacitor C to hold V
output of A2 low through D1 serves to turn off A1 so that V
remains constant.
the diodes of A1 to attenuate the input signal. Because the
output power of A1 is held constant, the RMS value is con-
stant and the attenuation is directly proportional to the RMS
value of the input voltage. The attenuation is also propor-
tional 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 potentiometer is set such
that V
O
IN
reads directly in RMS volts.
becomes more positive than V
O
equal to V
O
DS007981-31
. A1 then charges
IN
DS007981-30
PK. Pulling the
O