LM231A/LM231/LM331A/LM331

Precision Voltage-to-Frequency Converters

General Description

The LM231/LM331 family of voltage-to-frequency converters

are ideally suited for use in simple low-cost circuits for

analog-to-digital conversion, precision frequency-to-voltage

conversion, long-term integration, linear frequency modula-

tion or demodulation, and many other functions. The output

when used as a voltage-to-frequency converter is a pulse

train at a frequency precisely proportional to the applied in-

put voltage. Thus, it provides all the inherent advantages of

the voltage-to-frequency conversion techniques, and is easy

to apply in all standard voltage-to-frequency converter appli-

cations. Further, the LM231A/LM331A attain a new high

level of accuracy versus temperature which could only be at-

tained with expensive voltage-to-frequency modules. Addi-

tionally the LM231/331 are ideally suited for use in digital

systems at low power supply voltages and can provide

low-cost

analog-to-digital

conversion

in

microprocessor-controlled systems. And, the frequency from

a battery powered voltage-to-frequency converter can be

easily channeled through a simple photoisolator to provide

isolation against high common mode levels.

The LM231/LM331 utilize a new temperature-compensated

band-gap reference circuit, to provide excellent accuracy

over the full operating temperature range, at power supplies

as low as 4.0V. The precision timer circuit has low bias cur-

rents without degrading the quick response necessary for

100 kHz voltage-to-frequency conversion. And the output

are capable of driving 3 TTL loads, or a high voltage output

up to 40V, yet is short-circuit-proof against V

Features

n Guaranteed linearity 0.01% max

n Improved performance in existing voltage-to-frequency

conversion applications

n Split or single supply operation

n Operates on single 5V supply

n Pulse output compatible with all logic forms

n Low power dissipation, 15 mW typical at 5V

n Wide dynamic range, 100 dB min at 10 kHz full scale

frequency

n Wide range of full scale frequency, 1 Hz to 100 kHz

n Low cost

Typical Applications

DS005680-1

FIGURE 1. Simple Stand-Alone Voltage-to-Frequency Converter

June 1999

© 1999 National Semiconductor Corporation

DS005680

www.national.com