LM3911.PDF

June 1994

LM3911 Temperature Controller

General Description

The LM3911 is a highly accurate temperature measurement

and/or control system for use over a b 25 § Cto a 85 § C tem-

perature range. Fabricated on a single monolithic chip, it

includes a temperature sensor, a stable voltage reference

and an operational amplifier.

The output voltage of the LM3911 is directly proportional to

temperature in degrees Kelvin at 10 mV/ § K. Using the inter-

nal op amp with external resistors any temperature scale

factor is easily obtained. By connecting the op amp as a

comparator, the output will switch as the temperature trans-

verses the set-point making the device useful as an on-off

temperature controller.

An active shunt regulator is connected across the power

leads of the LM3911 to provide a stable 6.8V voltage refer-

ence for the sensing system. This allows the use of any

power supply voltage with suitable external resistors.

The input bias current is low and relatively constant with

temperature, ensuring high accuracy when high source im-

pedance is used. Further, the output collector can be re-

turned to a voltage higher than 6.8V allowing the LM3911 to

drive lamps and relays up to a 35V supply.

The LM3911 uses the difference in emitter-base voltage of

transistors operating at different current densities as the ba-

sic temperature sensitive element. Since this output de-

pends only on transistor matching the same reliability and

stability as present op amps can be expected.

The LM3911 is available in two package styles, a metal can

TO-46 and an 8-lead epoxy mini-DIP. In the epoxy package

all electrical connections are made on one side of the de-

vice allowing the other 4 leads to be used for attaching the

LM3911 to the temperature souce. The LM3911 is rated for

operation over a b 25 § Cto a 85 § C temperature range.

Features

Y Uncalibrated accuracy g 10 § C

Y Internal op amp with frequency compensation

Y Linear output of 10 mV/ § K (10 mV/ § C)

Y Can be calibrated in degrees Kelvin, Celsius or

Fahrenheit

Y Output can drive loads up to 35V

Y Internal stable voltage reference

Y Low cost

Block Diagram

Typical Applications

Ground Referred

Centigrade Thermometer

Proportioning Temperature

Controller

Basic Temperature Controller

* Output goes negative on

temperature increase

R S e (V a b 6.8V) k X

TL/H/5701±1

* Trims out initial zener tolerance.

Set output to read C

Note 1: C1 determines proportioning frequency f &

2R4 C1

Note 2: R10 e l V a l a l V b l b 7V

0.0015A

Note 3: Either V b or V a can be ground.

C 1995 National Semiconductor Corporation

TL/H/5701

RRD-B30M115/Printed in U. S. A.

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

Supply Current (Externally Set)

10 mA

Output Short Circuit Duration Indefinite

Operating Temperature Range b 25 § Cto a 85 § C

Storage Temperature Range b 65 § Cto a 150 § C

Lead Temperature (Soldering, 10 seconds)

260 § C

Output Collector Voltage, V aa

36V

Feedback Input Voltage Range

0V to a 7.0V

Electrical Characteristics (Note 1)

Parameter

Conditions

Min

Typ

Max

Units

SENSOR

Output Voltage

T A eb 25 § C, (Note 2)

2.36

2.48

2.60

Output Voltage

T A ea 25 § C, (Note 2)

2.88

2.98

3.08

Output Voltage

T A ea 85 § C, (Note 2)

3.46

3.58

3.70

Linearity

D T e 100 § C

0.5

Long-Term Stability

0.3

Repeatability

0.3

VOLTAGE REFERENCE

Reverse Breakdown Voltage

1 mA s I z s 5 mA

6.55

6.85

7.25

Reverse Breakdown Voltage

1 mA s I z s 5mA

Change With Current

Temperature Stability

Dynamic Impedance

I z e 1 mA

3.0

RMS Noise Voltage

10 Hz s f s 10 kHz

m V

Long Term Stability

T A ea 85 § C

6.0

OP AMP

Input Bias Current

T A ea 25 § C

150

Input Bias Current

250

Voltage Gain

R L e 36k, V aa e 36V

2500

15000

V/V

Output Leakage Current

T A e 25 § C (Note 3)

0.2

m A

Output Leakage Current

(Note 3)

1.0

m A

Output Source Current

V OUT s 3.70

m A

Output Sink Current

1V s V OUT s 36V

2.0

Note 1: These specifications apply for b 25 § C s T A s a 85 § C and 0.9 mA s I SUPPLY s 1.1 mA unless otherwise specified; C L s 50 pF.

Note 2: The output voltage applies to the basic thermometer configuration with the output and input terminals shorted and a load resistance of t 1.0 M X . This is

the feedback sense voltage and includes errors in both the sensor and op amp. This voltage is specified for the sensor in a rapidly stirred oil bath. The output is

referred to V a .

Note 3: The output leakage current is specified with t 100 mV overdrive. Since this voltage changes with temperature, the voltage drive for turn-off changes and is

defined as V OUT (with output and input shorted) b 100 mV. This specification applies for V OUT e 36V.

Application Hints

Although the LM3911 is designed to be totally trouble-free,

certain precautions should be taken to insure the best pos-

sible performance.

As with any temperature sensor, internal power dissipation

will raise the sensor's temperature above ambient. Nominal

suggested operating current for the shunt regulator is 1.0

mA and causes 7.0 mW of power dissipation. In free, still, air

this raises the package temperature by about 1.2 § K. Al-

though the regulator will operate at higher reverse currents

and the output will drive loads up to 5.0 mA, these higher

currents will raise the sensor temperature to about 19 § K

above ambient-degrading accuracy. Therefore, the sensor

should be operated at the lowest possible power level.

With moving air, liquid or surface temperature sensing, self-

heating is not as great a problem since the measured

media will conduct the heat from the sensor. Also, there are

many small heat sinks designed for transistors which will

improve heat transfer to the sensor from the surrounding

medium. A small finned clip-on heat sink is quite effective in

free-air. It should be mentioned that the LM3911 die is on

the base of the package and therefore coupling to the base

is preferable.

The internal reference regulator provides a temperature sta-

ble voltage for offsetting the output or setting a comparison

point in temperature controllers. However, since this refer-

ence is at the same temperature as the sensor temperature,

changes will also cause reference drift. For application

where maximum accuracy is needed an external reference

should be used. Of course, for fixed temperature controllers

the internal reference is adequate.

Typical Performance Characteristics

Temperature

Conversion

Op Amp Input Current

Power Supply Current

T CENTIGRADE e T C

T FAHRENHEIT e T F

T KELVIN e T K

T K e T C a 273.16

T C e (40 a T F ) 5

5 b 40

Output Saturation

Voltage

Thermal Time Constant

in Stirred Oil Bath

Thermal Time Constant in

Still Air

Supply Sensitivity

Device Temperature Rise

Reference Regulation

Turn ``ON'' Response

Amplifier Output Impedance

TL/H/5701±2

9 b 40

T F e (40 a T C ) 9

Schematic Diagram

Typical Applications (Continued)

Basic Thermometer for Negative Supply

Basic Thermometer

for Positive Supply

Increasing Output Drive

Note: Load current to GND

is supplied through R S

R S e (V b b 6.8V) c 10 3 X

RS e (V a b 6.8V) c 10 3 X

External Frequency Compensation

for Greater Stability when Driving

Capacitive Loads

Operating With External Zener for

Lower Power Dissipation

Temperature Controller With Hysteresis

* Depends on Zener current.

*Output goes positive on temperature increase

Set temperature

TL/H/5701±3

Typical Applications (Continued)

Thermometer With Meter Output

R1* e

Meter Thermometer With Trimmed Output

(VZ) 0.01 D T

I M (V Z b 0.01 T O )

Select I Q s

R2 e

0.01 T O b I Q R1

I Q

R3 e

V Z

I Q b R1 b R2

V z e Shunt regulator voltage (use 6.85)

D T e Meter temperature span ( § K)

I M e Meter full scale current (A)

T O e Meter zero temperature ( § K)

I Q e Current through R1, R2, R3 at zero

meter current (10 m A to 1.0 mA) (A)

*Values shown for:

T O e 300 § K, D T e 100 § K,

I M e 1.0 mA, I Q e 100 m A

**The 0.01 in the above and following equations is in units of V/ § KorV/ § C,

and is a result of the basic 0.01V/ § K sensitivity of the transducer

Ground Referred Thermometer

R1 e

I Q s

*Selected as for meter thermometer except T O should

be 5 § K more than desired and I Q e 100 m A

Calibrates T O

(V Z )(10mV)( D T)

V O

R L

(V Z b 0.01 T O )

Ground Referred Centigrade Thermometer

R2 e

0.01 T O b I Q R1

I Q

I Q b R1 b R2

V z e Shunt regulator voltage

D T e Temperature span ( § K)

T O e Temperature for zero output ( § K)

V O e Full scale output voltage s 10V

I Q e Current through R1, R2, R3

at zero output voltage

(typically 100 m A to 1.0 mA)

*Set zero

V Z b 0.01 T L

I H b

0.01 T H

V Z b 0.01 T H

0.01 T L

R1 b I L

R2 ( X ) e

0.01

R1 R3

T H (V Z b 0.01 T L ) b T L (V Z b 0.01 T H )

(

Two Terminal Temperature to Current Transducer*

V Z

T H

T L b 1

R3( X ) t

I L TH

T L

I H b

R4 e

(V Z b 0.01 T L )(R2)

(R2)(0.01 T L )

R1 a

V Z b 0.01 T L

R2 b I L

R2 a

T L e Temperature for I L (K)

T H e Temperature for I H (K)

V Z e Zener voltage (V)

I L e Low temperature output current (A)

I H e High temperature output current (A)

*Values shown for I OUT e 1mAto10mAfor10 § Fto100 § F

² Set temperature

TL/H/5701±4

**The 0.01 in the above and following equations is in units of V/ § KorV/ § C, and is a result of the basic 0.01V/ § K sensitivity of the transducer

R3 e

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