LM231, LM331

www.ti.com

SNOSBI2B – JUNE 1999 – REVISED MARCH 2013

APPLICATIONS INFORMATION

PRINCIPLES OF OPERATION

The LM231/331 are monolithic circuits designed for accuracy and versatile operation when applied as voltage-to-

frequency (V-to-F) converters or as frequency-to-voltage (F-to-V) converters. A simplified block diagram of the

LM231/331 is shown in Figure 14 and consists of a switched current source, input comparator, and 1-shot timer.

Figure 14. Simplified Block Diagram of Stand-Alone

Voltage-to-Frequency Converter and

External Components

Simplified Voltage-to-Frequency Converter

The operation of these blocks is best understood by going through the operating cycle of the basic V-to-F

converter, Figure 14, which consists of the simplified block diagram of the LM231/331 and the various resistors

and capacitors connected to it.

greater, the comparator will trigger the 1-shot timer. The output of the timer will turn ON both the frequency

the timer will reset itself.

to the level of V1. Then the comparator will trigger the timer and start another cycle.

provide a frequency precisely proportional to its input voltage over a wide range of frequencies.

Detail of Operation, Functional Block Diagram

The block diagram (FUNCTIONAL BLOCK DIAGRAM) shows a band gap reference which provides a stable 1.9

coefficient, and typically changes less than ½% over a 100°C temperature change.

current switch and the output driver transistor. When the voltage at pin 5 rises to

Copyright © 1999–2013, Texas Instruments Incorporated

Submit Documentation Feedback

7

Product Folder Links: LM231 LM331