LM331.PDF

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

f OUT e

2.09 V # R S

R L

R t C t

TL/H/5680±1

*Use stable components with low temperature coefficients. See Typical Applications section.

**0.1 m For1 m F, 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.

V IN

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

Output Short Circuit to Ground

Continuous

Output Short Circuit to V CC

Continuous

Input Voltage

b 0.2V to a V S

T MIN T MAX

Operating Ambient Temperature Range

b 55 § Cto a 125 § C

b 25 § Cto a 85 § C

0 § Cto 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

i jA

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

Metal Can Package (TO-5)

260 § C

ESD Susceptibility (Note 4)

Metal Can Package (TO-5)

2000V

Other Packages

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 Figure1

Scale

Conversion Accuracy Scale Factor (Gain) V IN eb 10V, R S e 14 k X

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 eb 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 eb 11V

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

Offset Current

g 8

g 100

Common-Mode Range

T MIN s T A s T MAX

b 0.2

V CC b 2.0 V

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

LM131/LM231/LM331

V PIN 5 e 10V

200

1000

LM131A/LM231A/LM331A

V PIN 5 e 10V

200

500

V SAT PIN 5 (Reset)

I e 5 mA

0.22

0.5

CURRENT SOURCE (Pin 1)

Output Current

R S e 14 k X ,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

LM231, LM231A, LM331, LM331A

0.02

10.0

All Devices

T A e T MAX

2.0

50.0

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

I e 3.2 mA (2 TTL Loads), T MIN s T A s T MAX

0.10

0.40

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 Figure3, 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 É , or polystyrene.

Note 4: Human body model, 100 pF discharged through a 1.5 k X resistor.

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 É registered trademark of DuPont

Typical Performance Characteristics

(All electrical characteristics apply for the circuit of Figure3, unless otherwise noted.)

Nonlinearity Error, LM131

Family, as Precision V-to-F

Converter (Figure3)

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 (Figure4)

Nonlinearity Error, LM131

(Figure1)

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 (Figure6)

TL/H/5680±3

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