LM13700N National Semiconductor, LM13700N Datasheet - Page 22

• 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

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Additional Applications
The circuit of Figure 28 is a voltage reference of variable
Temperature Coefficient. The 100 kΩ potentiometer adjusts
the output voltage which has a positive TC above 1.2V, zero
TC at about 1.2V, and negative TC below 1.2V. This is
accomplished by balancing the TC of the A2 transfer function
against the complementary TC of D1.
The wide dynamic range of the LM13700 allows easy control
of the output pulse width in the Pulse Width Modulator of
Figure 29.
For generating I
current, the system of Figure 30 provides a logarithmic cur-
rent out for a linear voltage in.
Since the closed-loop configuration ensures that the input to
A2 is held equal to 0V, the output current of A1 is equal to
I
The differential voltage between Q1 and Q2 is attenuated by
the R1,R2 network so that A1 may be assumed to be oper-
ating within its linear range. From Equation (5), the input
voltage to A1 is:
3
= −V
C
/R
C
.
ABC
over a range of 4 to 6 decades of
(Continued)
FIGURE 27. True RMS Converter
22
The voltage on the base of Q1 is then
The ratio of the Q1 and Q2 collector currents is defined by:
Combining and solving for I
This logarithmic current can be used to bias the circuit of
Figure 4 to provide temperature independent stereo attenu-
ation characteristic.
ABC
yields:
00798134