LM231A/LM231/LM331A/LM331 Precision Voltage-to-Frequency Converters
June 1999
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
CC
.
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
Excellent temperature stability,
±
50 ppm/˚C max
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
*
Use stable components with low temperature coefficients. See Typical Applications section.
**
0.1µF or 1µF, See “Principles of Operation.”
FIGURE 1. Simple Stand-Alone Voltage-to-Frequency Converter
with
±
0.03% Typical Linearity (f = 10 Hz to 11 kHz)
Teflon
®
is a registered trademark of DuPont
© 1999 National Semiconductor Corporation
DS005680
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
