TL H 5680
LM131ALM131
LM231ALM231
LM331ALM331
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
Guaranteed linearity 0 01% max
Y
Improved performance in existing voltage-to-frequency
conversion applications
Y
Split or single supply operation
Y
Operates on single 5V supply
Y
Pulse output compatible with all logic forms
Y
Excellent temperature stability
g
50 ppm C max
Y
Low power dissipation 15 mW typical at 5V
Y
Wide dynamic range 100 dB min at 10 kHz full scale
frequency
Y
Wide range of full scale frequency 1 Hz to 100 kHz
Y
Low cost
Typical Applications
TL H 5680 1
Use stable components with low temperature coefficients See Typical Applications section
f
OUT
e
V
IN
2 09 V
R
S
R
L
1
R
t
C
t
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)
C1995 National Semiconductor Corporation
RRD-B30M115 Printed in U S A
Absolute Maximum Ratings
(Note 1)
If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office
Distributors for availability and specifications
LM131A LM131
LM231A LM231
LM331A LM331
Supply Voltage
40V
40V
40V
Output Short Circuit to Ground
Continuous
Continuous
Continuous
Output Short Circuit to V
CC
Continuous
Continuous
Continuous
Input Voltage
b
0 2V to
a
V
S
b
0 2V to
a
V
S
b
0 2V to
a
V
S
T
MIN
T
MAX
T
MIN
T
MAX
T
MIN
T
MAX
Operating Ambient Temperature Range
b
55 C to
a
125 C
b
25 C to
a
85 C
0 C to
a
70 C
Power Dissipation (P
D
at 25 C)
and Thermal Resistance (i
jA
)
(H Package) P
D
670 mW
i
jA
150 C W
(N Package) P
D
1 25W
1 25W
i
jA
100 C W
100 C W
(M Package) P
D
1 25W
i
JA
85 C W
Lead Temperature (Soldering 10 sec )
Dual-In-Line Package (Plastic)
260 C
260 C
260 C
Metal Can Package (TO-5)
260 C
ESD Susceptibility (Note 4)
Metal Can Package (TO-5)
2000V
Other Packages
500V
500V
Electrical Characteristics
T
A
e
25 C unless otherwise specified (Note 2)
Parameter
Conditions
Min
Typ
Max
Units
VFC Non-Linearity (Note 3)
4 5V
s
V
S
s
20V
g
0 003
g
0 01
% Full-
Scale
T
MIN
s
T
A
s
T
MAX
g
0 006
g
0 02
% Full-
Scale
VFC Non-Linearity
V
S
e
15V f
e
10 Hz to 11 kHz
g
0 024
g
0 14
%Full-
In Circuit of
Figure 1
Scale
Conversion Accuracy Scale Factor (Gain)
V
IN
e b
10V R
S
e
14 kX
LM131 LM131A LM231 LM231A
0 95
1 00
1 05
kHz V
LM331 LM331A
0 90
1 00
1 10
kHz V
Temperature Stability of Gain
T
MIN
s
T
A
s
T
MAX
4 5V
s
V
S
s
20V
LM131 LM231 LM331
g
30
g
150
ppm C
LM131A LM231A LM331A
g
20
g
50
ppm C
Change of Gain with V
S
4 5V
s
V
S
s
10V
0 01
0 1
% V
10V
s
V
S
s
40V
0 006
0 06
% V
Rated Full-Scale Frequency
V
IN
e b
10V
10 0
kHz
Gain Stability vs Time
T
MIN
s
T
A
s
T
MAX
g
0 02
% Full-
(1000 Hrs)
Scale
Overrange (Beyond Full-Scale) Frequency
V
IN
e b
11V
10
%
INPUT COMPARATOR
Offset Voltage
g
3
g
10
mV
LM131 LM231 LM331
T
MIN
s
T
A
s
T
MAX
g
4
g
14
mV
LM131A LM231A LM331A
T
MIN
s
T
A
s
T
MAX
g
3
g
10
mV
Bias Current
b
80
b
300
nA
Offset Current
g
8
g
100
nA
Common-Mode Range
T
MIN
s
T
A
s
T
MAX
b
0 2
V
CC
b
2 0
V
2
Electrical Characteristics
T
A
e
25 C unless otherwise specified (Note 2) (Continued)
Parameter
Conditions
Min
Typ
Max
Units
TIMER
Timer Threshold Voltage Pin 5
0 63
0 667
0 70
c
V
S
Input Bias Current Pin 5
V
S
e
15V
All Devices
0V
s
V
PIN 5
s
9 9V
g
10
g
100
nA
LM131 LM231 LM331
V
PIN 5
e
10V
200
1000
nA
LM131A LM231A LM331A
V
PIN 5
e
10V
200
500
nA
V
SAT PIN 5
(Reset)
I
e
5 mA
0 22
0 5
V
CURRENT SOURCE (Pin 1)
Output Current
R
S
e
14 kX V
PIN 1
e
0
LM131 LM131A LM231 LM231A
126
135
144
m
A
LM331 LM331A
116
136
156
m
A
Change with Voltage
0V
s
V
PIN 1
s
10V
0 2
1 0
m
A
Current Source OFF Leakage
LM131 LM131A
0 01
1 0
nA
LM231 LM231A LM331 LM331A
0 02
10 0
nA
All Devices
T
A
e
T
MAX
2 0
50 0
nA
Operating Range of Current (Typical)
(10 to 500)
m
A
REFERENCE VOLTAGE (Pin 2)
LM131 LM131A LM231 LM231A
1 76
1 89
2 02
V
DC
LM331 LM331A
1 70
1 89
2 08
V
DC
Stability vs Temperature
g
60
ppm C
Stability vs Time 1000 Hours
g
0 1
%
LOGIC OUTPUT (Pin 3)
V
SAT
I
e
5 mA
0 15
0 50
V
I
e
3 2 mA (2 TTL Loads) T
MIN
s
T
A
s
T
MAX
0 10
0 40
V
OFF Leakage
g
0 05
1 0
m
A
SUPPLY CURRENT
LM131 LM131A LM231
V
S
e
5V
2 0
3 0
4 0
mA
LM231A
V
S
e
40V
2 5
4 0
6 0
mA
LM331 LM331A
V
S
e
5V
1 5
3 0
6 0
mA
V
S
e
40V
2 0
4 0
8 0
mA
Note 1
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur DC and AC electrical specifications do not apply when operating
the device beyond its specified operating conditions
Note 2
All specifications apply in the circuit of
Figure 3 with 4 0V
s
V
S
s
40V unless otherwise noted
Note 3
Nonlinearity is defined as the deviation of f
OUT
from V
IN
c
(10 kHz
b
10 V
DC
) when the circuit has been trimmed for zero error at 10 Hz and at 10 kHz
over the frequency range 1 Hz to 11 kHz For the timing capacitor C
T
use NPO ceramic Teflon
or polystyrene
Note 4
Human body model 100 pF discharged through a 1 5 kX resistor
3
Functional Block Diagram
TL H 5680 2
Pin numbers apply to 8-pin packages only See connection diagram for LM231WM pin numbers
FIGURE 1a
Teflon
registered trademark of DuPont
4
Typical Performance Characteristics
(All electrical characteristics apply for the circuit of
Figure 3 unless otherwise noted )
Nonlinearity Error LM131
Family as Precision V-to-F
Converter (
Figure 3 )
Nonlinearity Error LM131
Family
Nonlinearity vs Power Supply
Voltage
Frequency vs Temperature
LM131A
V
REF
vs Temperature
LM131A
Output Frequency vs
V
SUPPLY
100 kHz Nonlinearity Error
LM131 Family (
Figure 4 )
Nonlinearity Error LM131
(
Figure 1 )
Input Current (Pins 6 7) vs
Temperature
Power Drain vs V
SUPPLY
Output Saturation Voltage vs
I
OUT
(Pin 3)
Nonlinearity Error Precision
F-to-V Converter (
Figure 6 )
TL H 5680 3
5
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