LM131A LM131 LM231A LM231 LM331A LM331 Precision Voltage-to-Frequency Converters
December 1994
LM131A LM131 LM231A LM231 LM331A LM331
Precision Voltage-to-Frequency Converters
General Description
The LM131 LM231 LM331 family of voltage-to-frequency
converters are ideally suited for use in simple low-cost cir-
cuits for analog-to-digital conversion precision frequency-
to-voltage conversion long-term integration linear frequen-
cy modulation 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 input voltage Thus it provides all the inherent ad-
vantages of the voltage-to-frequency conversion tech-
niques and is easy to apply in all standard voltage-to-fre-
quency converter applications Further the LM131A
LM231A LM331A attains a new high level of accuracy ver-
sus temperature which could only be attained with expen-
sive voltage-to-frequency modules Additionally the LM131
is ideally suited for use in digital systems at low power sup-
ply voltages and can provide low-cost analog-to-digital con-
version in microprocessor-controlled systems And the fre-
quency from a battery powered voltage-to-frequency con-
verter can be easily channeled through a simple photoisola-
tor to provide isolation against high common mode levels
The LM131 LM231 LM331 utilizes a new temperature-
compensated band-gap reference circuit to provide excel-
lent accuracy over the full operating temperature range at
power supplies as low as 4 0V The precision timer circuit
has low bias currents without degrading the quick response
necessary for 100 kHz voltage-to-frequency conversion
And the output is capable of driving 3 TTL loads or a high
voltage output up to 40V yet is short-circuit-proof against
V
CC
Features
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Guaranteed linearity 0 01% max
Improved performance in existing voltage-to-frequency
conversion applications
Split or single supply operation
Operates on single 5V supply
Pulse output compatible with all logic forms
Excellent temperature stability
g
50 ppm C max
Low power dissipation 15 mW typical at 5V
Wide dynamic range 100 dB min at 10 kHz full scale
frequency
Wide range of full scale frequency 1 Hz to 100 kHz
Low cost
Typical Applications
f
OUT
e
V
IN
R
1
S
2 09 V R
L
R
t
C
t
TL H 5680 – 1
Use stable components with low temperature coefficients See Typical Applications section
0 1mF or 1mF See ‘‘Principles of Operation ’’
FIGURE 1 Simple Stand-Alone Voltage-to-Frequency Converter
with
g
0 03% Typical Linearity (f
e
10 Hz to 11 kHz)
C
1995 National Semiconductor Corporation
TL H 5680
RRD-B30M115 Printed in U S A
NSC [ NATIONAL SEMICONDUCTOR ]
