LM231A/231/331A/331
LM231A/LM231/LM331A/LM331 Precision Voltage-to-Frequency Converters
1
FEATURES
Ensured 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: ±50 ppm/°C
max
Low Power Consumption: 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
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
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 advantages of the voltage-to-frequency
conversion techniques, and is easy to apply in all
standard voltage-to-frequency converter applications.
Further, the LM231A/LM331A attain a new high level
of accuracy versus temperature which could only be
attained
with
expensive
voltage-to-frequency
modules. Additionally 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 photo isolator 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 currents 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
.
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CONNECTION DIAGRAM
Figure 1. Plastic Dual-In-Line Package (PDIP)
See Package Number P (R-PDIP-T8)
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LM231A/231/331A/331
Absolute Maximum Ratings
(1) (2) (3)
Supply Voltage, V
S
Output Short Circuit to Ground
Output Short Circuit to V
CC
Input Voltage
Package Dissipation at 25°C
Lead Temperature (Soldering, 10 sec.)
PDIP
ESD Susceptibility
(1)
(2)
(3)
(4)
(5)
40V
Continuous
Continuous
−0.2V
to +V
S
1.25W
(4)
260°C
500V
(5)
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.
All voltages are measured with respect to GND = 0V, unless otherwise noted.
If Military/Aerospace specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications.
The absolute maximum junction temperature (T
J
max) for this device is 150°C. The maximum allowable power dissipation is dictated by
T
J
max, the junction-to-ambient thermal resistance (θ
JA
), and the ambient temperature T
A
, and can be calculated using the formula
P
D
max = (T
J
max - T
A
) /
θ
JA
. The values for maximum power dissipation will be reached only when the device is operated in a severe
fault condition (e.g., when input or output pins are driven beyond the power supply voltages, or the power supply polarity is reversed).
Obviously, such conditions should always be avoided.
Human body model, 100 pF discharged through a 1.5 kΩ resistor.
(1)
Operating Ratings
LM231, LM231A
LM331, LM331A
Supply Voltage, V
S
(1)
Operating Ambient Temperature
−25°C
to +85°C
0°C to +70°C
+4V to +40V
All voltages are measured with respect to GND = 0V, unless otherwise noted.
Package Thermal Resistance
Package
8-Lead PDIP
θ
J-A
100°C/W
Electrical Characteristics
All specifications apply in the circuit of Figure 16, with 4.0V
≤
V
S
≤
40V, T
A
=25°C, unless otherwise specified.
Parameter
VFC Non-Linearity
(1)
Conditions
4.5V
≤
V
S
≤
20V
T
MIN
≤
T
A
≤
T
MAX
V
S
= 15V, f = 10 Hz to 11 kHz
V
IN
=
−10V,
R
S
= 14 kΩ
Min
Typ
±0.003
±0.006
±0.024
Max
±0.01
±0.02
±0.14
1.05
1.10
±150
±50
0.1
0.06
Units
% Full- Scale
% Full- Scale
%Full- Scale
kHz/V
kHz/V
ppm/°C
ppm/°C
%/V
%/V
kHz
% Full- Scale
VFC Non-Linearity in Circuit of Figure 15
Conversion Accuracy Scale Factor (Gain)
LM231, LM231A
LM331, LM331A
Temperature Stability of Gain
LM231/LM331
LM231A/LM331A
Change of Gain with V
S
Rated Full-Scale Frequency
Gain Stability vs. Time (1000 Hours)
0.95
0.90
1.00
1.00
±30
±20
0.01
0.006
T
MIN
≤
T
A
≤
T
MAX
, 4.5V
≤
V
S
≤
20V
4.5V
≤
V
S
≤
10V
10V
≤
V
S
≤
40V
V
IN
=
−10V
T
MIN
≤
T
A
≤
T
MAX
10.0
±0.02
(1)
Nonlinearity is defined as the deviation of f
OUT
from V
IN
× (10 kHz/−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.
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LM231A/231/331A/331
Electrical Characteristics (continued)
All specifications apply in the circuit of Figure 16, with 4.0V
≤
V
S
≤
40V, T
A
=25°C, unless otherwise specified.
Parameter
Over Range (Beyond Full-Scale) Frequency
INPUT COMPARATOR
Offset Voltage
LM231/LM331
LM231A/LM331A
Bias Current
Offset Current
Common-Mode Range
TIMER
Timer Threshold Voltage, Pin 5
Input Bias Current, Pin 5
All Devices
LM231/LM331
LM231A/LM331A
V
SAT PIN 5
(Reset)
CURRENT SOURCE (Pin 1)
Output Current
LM231, LM231A
LM331, LM331A
Change with Voltage
Current Source OFF Leakage
LM231, LM231A, LM331, LM331A
All Devices
Operating Range of Current (Typical)
REFERENCE VOLTAGE (Pin 2)
LM231, LM231A
LM331, LM331A
Stability vs. Temperature
Stability vs. Time, 1000 Hours
LOGIC OUTPUT (Pin 3)
I = 5 mA
V
SAT
OFF Leakage
SUPPLY CURRENT
LM231, LM231A
LM331, LM331A
V
S
= 5V
V
S
= 40V
V
S
= 5V
V
S
= 40V
2.0
2.5
1.5
2.0
3.0
4.0
3.0
4.0
4.0
6.0
6.0
8.0
mA
mA
mA
mA
I = 3.2 mA (2 TTL Loads), T
MIN
≤
T
A
≤
T
MAX
0.15
0.10
±0.05
0.50
0.40
1.0
V
V
μA
1.76
1.70
1.89
1.89
±60
±0.1
2.02
2.08
V
DC
V
DC
ppm/°C
%
T
A
= T
MAX
0.02
2.0
(10 to 500)
10.0
50.0
nA
nA
μA
0V
≤
V
PIN 1
≤
10V
R
S
= 14 kΩ, V
PIN 1
= 0
126
116
135
136
0.2
144
156
1.0
μA
μA
μA
V
S
= 15V
0V
≤
V
PIN 5
≤
9.9V
V
PIN 5
= 10V
V
PIN 5
= 10V
I = 5 mA
±10
200
200
0.22
±100
1000
500
0.5
nA
nA
nA
V
0.63
0.667
0.70
× V
S
T
MIN
≤
T
A
≤
T
MAX
−0.2
T
MIN
≤
T
A
≤
T
MAX
T
MIN
≤
T
A
≤
T
MAX
±3
±4
±3
−80
±8
±10
±14
±10
−300
±100
V
CC
−2.
0
mV
mV
mV
nA
nA
V
V
IN
=
−11V
Conditions
Min
10
Typ
Max
Units
%
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LM231A/231/331A/331
FUNCTIONAL BLOCK DIAGRAM
Pin numbers apply to 8-pin packages only.
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LM231A/231/331A/331
TYPICAL PERFORMANCE CHARACTERISTICS
(All electrical characteristics apply for the circuit of Figure 16, unless otherwise noted.)
Nonlinearity Error
as Precision V-to-F
Converter (Figure 16)
Nonlinearity Error
Figure 2.
Nonlinearity Error
vs.
Power
Supply Voltage
Figure 3.
Frequency
vs.
Temperature
Figure 4.
V
REF
vs.
Temperature
Figure 5.
Output Frequency
vs.
V
SUPPLY
Figure 6.
Figure 7.
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