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 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-fre- quency converter applications. Further, the LM131A/ LM231A/LM331A attains a new high level of accuracy versus temperature which could only be attained with expensive voltage-to-frequency modules. Additionally the LM131 is 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 LM131/LM231/LM331 utilizes a new temperaturecompensated 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 is capable of driving 3 TTL loads, or a high voltage output up to 40V, yet is short-circuit-proof against VCC.
Features
YGuaranteed linearity 0.01% max
YImproved performance in existing voltage-to-frequency conversion applications
YSplit or single supply operation
YOperates on single 5V supply
YPulse output compatible with all logic forms
YExcellent temperature stability, g50 ppm/§C max
YLow power dissipation, 15 mW typical at 5V
YWide dynamic range, 100 dB min at 10 kHz full scale frequency
YWide range of full scale frequency, 1 Hz to 100 kHz
YLow cost
Typical Applications
fOUT e |
VIN |
# |
RS |
# |
1 |
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TL/H/5680 ± 1 |
2.09 V |
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RtCt |
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RL |
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*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 g0.03% Typical Linearity (f e 10 Hz to 11 kHz)
Converters Frequency-to-Voltage Precision LM331A/LM331 LM231A/LM231, LM131A/LM131,
C1995 National Semiconductor Corporation |
TL/H/5680 |
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.
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LM131A/LM131 |
LM231A/LM231 |
LM331A/LM331 |
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Supply Voltage |
40V |
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40V |
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40V |
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Output Short Circuit to Ground |
Continuous |
Continuous |
Continuous |
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Output Short Circuit to VCC |
Continuous |
Continuous |
Continuous |
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Input Voltage |
b0.2V to aVS |
b0.2V to aVS |
b0.2V to aVS |
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TMIN |
TMAX |
TMIN |
TMAX |
TMIN |
TMAX |
Operating Ambient Temperature Range |
b55§C to a125§C |
b25§C to a85§C |
0§C to a70§C |
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Power Dissipation (PD at 25§C) |
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and Thermal Resistance (ijA) |
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(H Package) PD |
670 mW |
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ijA |
150§C/W |
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(N Package) PD |
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1.25W |
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1.25W |
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ijA |
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100§C/W |
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100§C/W |
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(M Package) PD |
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1.25W |
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iJA |
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85§C/W |
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Lead Temperature (Soldering, 10 sec.) |
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Dual-In-Line Package (Plastic) |
260§C |
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260§C |
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260§C |
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Metal Can Package (TO-5) |
260§C |
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ESD Susceptibility (Note 4) |
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Metal Can Package (TO-5) |
2000V |
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Other Packages |
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500V |
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500V |
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Electrical Characteristics TAe25§C unless otherwise specified (Note 2)
Parameter |
Conditions |
Min |
Typ |
Max |
Units |
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VFC Non-Linearity (Note 3) |
4.5V s VS s 20V |
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g0.003 |
g0.01 |
% Full- |
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Scale |
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TMIN s TA s TMAX |
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g0.006 |
g0.02 |
% Full- |
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Scale |
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VFC Non-Linearity |
VS e 15V, f e 10 Hz to 11 kHz |
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g0.024 |
g0.14 |
%Full- |
In Circuit of Figure 1 |
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Scale |
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Conversion Accuracy Scale Factor (Gain) |
VIN e b10V, RS e 14 kX |
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LM131, LM131A, LM231, LM231A |
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0.95 |
1.00 |
1.05 |
kHz/V |
LM331, LM331A |
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0.90 |
1.00 |
1.10 |
kHz/V |
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Temperature Stability of Gain |
TMIN s TA s TMAX, 4.5V s VS s 20V |
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ppm/§C |
LM131/LM231/LM331 |
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g30 |
g150 |
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LM131A/LM231A/LM331A |
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g20 |
g50 |
ppm/§C |
Change of Gain with VS |
4.5VsVS s 10V |
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0.01 |
0.1 |
%/V |
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10V s VS s 40V |
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0.006 |
0.06 |
%/V |
Rated Full-Scale Frequency |
VIN e b10V |
10.0 |
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kHz |
Gain Stability vs Time |
TMIN s TA s TMAX |
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g0.02 |
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% Full- |
(1000 Hrs) |
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Scale |
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Overrange (Beyond Full-Scale) Frequency |
VIN e b11V |
10 |
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% |
INPUT COMPARATOR |
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Offset Voltage |
TMIN s TA s TMAX |
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g3 |
g10 |
mV |
LM131/LM231/LM331 |
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g4 |
g14 |
mV |
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LM131A/LM231A/LM331A |
TMIN s TA s TMAX |
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g3 |
g10 |
mV |
Bias Current |
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b80 |
b300 |
nA |
Offset Current |
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g8 |
g100 |
nA |
Common-Mode Range |
TMIN s TA s TMAX |
b0.2 |
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VCCb2.0 |
V |
2
Electrical Characteristics TAe25§C unless otherwise specified (Note 2) (Continued)
Parameter |
Conditions |
Min |
Typ |
Max |
Units |
TIMER |
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Timer Threshold Voltage, Pin 5 |
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0.63 |
0.667 |
0.70 |
c VS |
Input Bias Current, Pin 5 |
VS e 15V |
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All Devices |
0VsVPIN 5 s 9.9V |
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g10 |
g100 |
nA |
LM131/LM231/LM331 |
VPIN 5 e 10V |
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200 |
1000 |
nA |
LM131A/LM231A/LM331A |
VPIN 5 e 10V |
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200 |
500 |
nA |
VSAT PIN 5 (Reset) |
I e 5 mA |
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0.22 |
0.5 |
V |
CURRENT SOURCE (Pin 1) |
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Output Current |
RSe14 kX, VPIN 1e0 |
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LM131, LM131A, LM231, LM231A |
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126 |
135 |
144 |
mA |
LM331, LM331A |
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116 |
136 |
156 |
mA |
Change with Voltage |
0VsVPIN 1s10V |
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0.2 |
1.0 |
mA |
Current Source OFF Leakage |
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LM131, LM131A |
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0.01 |
1.0 |
nA |
LM231, LM231A, LM331, LM331A |
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0.02 |
10.0 |
nA |
All Devices |
TAeTMAX |
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2.0 |
50.0 |
nA |
Operating Range of Current (Typical) |
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(10 to 500) |
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mA |
REFERENCE VOLTAGE (Pin 2) |
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LM131, LM131A, LM231, LM231A |
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1.76 |
1.89 |
2.02 |
VDC |
LM331, LM331A |
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1.70 |
1.89 |
2.08 |
VDC |
Stability vs Temperature |
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g60 |
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ppm/§C |
Stability vs Time, 1000 Hours |
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g0.1 |
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% |
LOGIC OUTPUT (Pin 3) |
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VSAT |
Ie5 mA |
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0.15 |
0.50 |
V |
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Ie3.2 mA (2 TTL Loads), TMINsTAsTMAX |
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0.10 |
0.40 |
V |
OFF Leakage |
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g0.05 |
1.0 |
mA |
SUPPLY CURRENT |
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LM131, LM131A, LM231, |
VSe5V |
2.0 |
3.0 |
4.0 |
mA |
LM231A |
VSe40V |
2.5 |
4.0 |
6.0 |
mA |
LM331, LM331A |
VSe5V |
1.5 |
3.0 |
6.0 |
mA |
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VSe40V |
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 4.0VsVSs40V, unless otherwise noted.
Note 3: Nonlinearity is defined as the deviation of fOUT from VIN c (10 kHz/b10 VDC) 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, CT, use NPO ceramic, TeflonÉ, 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
TeflonÉ registered trademark of DuPont
4
Typical Performance Characteristics
(All electrical characteristics apply for the circuit of Figure 3 , unless otherwise noted.)
Nonlinearity Error, LM131 |
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Family, as Precision V-to-F |
Nonlinearity Error, LM131 |
Nonlinearity vs Power Supply |
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Converter (Figure 3 ) |
Family |
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Voltage |
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vs
6 )
TL/H/5680 ± 3
5
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