LM35 Temperature Sensor User Manual

So how does it show temperature? The answer is to display the output voltage, but not degrees Celsius. Why? Because its output voltage is linearly proportional to Centigrade temperature. Using the basic diode principle, when the temperature increases, the voltage across a diode increases at a certain rate. Next, let's take a full look at the LM35.

 

LM35 Specifications

• Calibrated Directly in Celsius (Centigrade)

• Linear + 10-mV/°C Scale Factor

• 0.5°C Ensured Accuracy (at 25°C)

• Rated for Full −55°C to 150°C Range

• Suitable for Remote Applications

• Low-Cost Due to Wafer-Level Trimming

• Operates From 4 V to 30 V

• Less Than 60-µA Current Drain

• Low Self-Heating, 0.08°C in Still Air

• Non-Linearity Only ±¼°C Typical

• Low-Impedance Output, 0.1 Ω for 1-mA Load

• Temperature coefficient is positive.

• Termination type is solder.

 

• Supply Voltage+35V to −0.2V

• Output Voltage+6V to −1.0V

• Output Current 10mA

• Storage Temp:

   TO-46 Package,−60°C to +180°C

   TO-92 Package,−60°C to +150°C

   SO-8 Package,−65°C to +150°C

   TO-220 Package,−65°C to +150°C

• Lead Temp:

   TO-46 Package,(Soldering, 10 seconds)  300°C

   TO-92 and TO-220 Package,(Soldering, 10 seconds)260°C

• SO Package:

   Vapor Phase (60 seconds) 215°C

   Infrared (15 seconds) 220°C

   ESD Susceptibility 2500V

• Specified Operating Temperature Range: TMIN to TMAX

   LM35, LM35A −55 ̊C to +150°C

   LM35C, LM35CA −40°C to +110°C

   LM35D  0°C to +100

 

• TO-46 Metal Can Package • Case is connected to negative pin (GN) • LM35H, LM35AH, LM35CH, LM35CAH, and LM35DH are available.	• SO-8 Small Outline Molded Package • LM35DM is available.
• TO-92 Plastic Package • LM35CZ, LM35CAZ, and LM35DZ are available.	• TO-220 Plastic Package • Tab is connected to the negative pin (GND). Note:The LM35DT pinout is different than the discontinued LM35DP • LM35DT is available.
Representation of the LM35 Package Family

 

Device	Status	Package Name	Package Type
LM35AH	ACTIVE	NDV	TO
LM35AH/NOPB	ACTIVE	NDV	TO
LM35CAH	ACTIVE	NDV	TO
LM35CAH/NOPB	ACTIVE	NDV	TO
LMCAZ/NOPB	ACTIVE	LP	TO-92
LMCAZ/LFT4	ACTIVE	LP	TO-92
LM35CH	ACTIVE	NDV	TO
LM35CH/NOPB	ACTIVE	NDV	TO
LM35CZ/NOPB	ACTIVE	LP	TO-92
LM35DH	ACTIVE	NDV	TO
LM35DH/NOPB	ACTIVE	NDV	TO
LM35DM	NRND	D	SOIC
LM35DM/NOPB	ACTIVE	D	SOIC
LM35DT	NRND	NEB	TO-220
LM35DT/NOPB	ACTIVE	NEB	TO-220
LM35DZ	ACTIVE	LP	TO-92
LM35H	ACTIVE	NDV	TO
LM35H/NOPB	ACTIVE	NDV	TO

 

Pin Number	Pin Name	Description
1	Vcc	Power pin, can be connected to 4V or 32V
2	Analog Out	Analog output pin, the output voltage is proportional to the temperature
3	GND	Ground pin

 

Figure 1: LM35 Circuit Symbol

Figure 2: LM35 Footprint

Figure 3: LM35DT 3D Mode

 

LM35 Alternative Specifications

LM35DT/NOPB
Parameter	Conditions
Source Content uid	LM35DT/NOPB
Pbfree Code	Yes
Rohs Code	Yes
Part Life Cycle Code	Active
Ihs Manufacturer	TEXAS INSTRUMENTS INC
Package Description	SIP3,.1TB
Reach Compliance Code	compliant
ECCN Code	EAR99
HTS Code	8542.39.00.01
Accuracy-Max (Cel)	1.5 Cel
Body Breadth	4.57 mm
Body Height	14.98 mm
Body Length or Diameter	10.16 mm
Housing	PLASTIC
JESD-609 Code	e3
Linearity (Cel)	0.2 Cel
Mounting Feature	THROUGH HOLE MOUNT
Number of Terminals	3
Operating Current-Max	0.114 mA
Operating Temperature-Max	100 °C
Output Interface Type	2-WIRE INTERFACE
Package Body Material	UNSPECIFIED
Package Equivalence Code	SIP3,.1TB
Package Shape/Style	RECTANGULAR
Power Supplies	4/30 V
R0-Nom	0.4 Ω
Sensors/Transducers Type	TEMPERATURE SENSOR,ANALOG,VOLTAGE OUTPUT
Supply Voltage-Max	30 V
Supply Voltage-Min	4 V
Surface Mount	NO
Temperature Coefficient	POSITIVE ppm/°C
Terminal Finish	MATTE TIN
Termination Type	SOLDER

 

LM35 Applications

The LM35 is an integrated-circuit temperature sensor whose output voltage changes according to the surrounding temperature. Power the LM35 by applying a regulated voltage such as +5V (VS) to the input pin and connecting the ground pin to the circuit's ground.

Figure 4: LM35 Function Schematic Diagram

1) As a Basic Celsius Temperature Sensor

The basic sensor only allows to measure +ve temperature in the range of 2°C to 150°C.

Figure 5: As a Basic Celsius Temperature Sensor

In the above circuit, you just need to power the LM35 and connect its output to the ADC. This circuit also works with an 80k ~ 100k resistor connected between the GND and Vout. Therefore, this connection will prevent it from voltage floating. If the temperature is 0°C, the output voltage will also be 0. When the temperature rises by 1 degree, it will increase by 0.01V (10mV). Another very important point, voltage can be converted to temperature using the following formula.

Note:

VOUT is the LM35 output voltage

T is the temperature in °C

2) As a Full-range Celsius Temperature Sensor

Full-range sensors allow the use of all temperature sensors that further measure temperatures ranging from -55°C to 150°C, with higher accuracy than basic temperature sensors.

Figure 6: As a Full-range Celsius Temperature Sensor

As for the above circuit, we connected an external resistor which eventually switches the negative voltage level up. We can further use the formula R1= -Vs/50µA to calculate the value of the external resistor.

 

LM35 Connection

Figure 7: Using LM35 with LM741 Op Amp

The LM35 circuit uses the operational amplifier IC741 as a comparator, which is configured as a non-inverting amplifier. This means that when the LM35 detects a high temperature, the output of the op amp goes to +ve and the red LED lights on, and when the temperature drops below the specified level, the output of the op amp goes to -ve and the green LED on.

Figure 8: Use LM35 in Temperature Measuring Circuit

The high temperature level can be set with the help of a preset in the circuit. When the red LED light turns on, you need to know the actual temperature at which the circuit is being tested, and a multimeter can be used here.

According to theory, the output voltage of LM35 increases by 1 degree Celsius, the output voltage will increase by 10mV. We can use a multimeter to measure the output voltage. For example, if the voltage is 322mV, the temperature here is 32.2℃.

 

An LM35 based precision temperature controller can be built to control an external load such as a heater or fan by connecting a relay driver stage to our previous controller as follows:

Figure 9: Use LM35 in Relay Controlling Circuit