LM35 — Precision Centigrade Temperature Sensor

Overview

The LM35 is a precision integrated-circuit temperature sensor manufactured by Texas Instruments. Its output voltage is linearly proportional to the Celsius (Centigrade) temperature, scaling at $10\text{ mV/}^\circ\text{C}$ .

Unlike thermistors, the LM35 requires no external calibration or signal conditioning circuit to deliver typical accuracies of $\pm 0.25\text{ }^\circ\text{C}$ at room temperature and $\pm 0.75\text{ }^\circ\text{C}$ over a full $-55^\circ\text{C}\text{ to }+150^\circ\text{C}$ range. It draws only 60 µA from its supply, resulting in minimal self-heating ( $< 0.1\text{ }^\circ\text{C}$ in still air).

Quick reference


Supply voltage (`VCC`)	4.0 V to 30.0 V DC
Output scale factor	$10.0\text{ mV / }^\circ\text{C}$ ( $0\text{ mV}$ at $0^\circ\text{C}$ , $250\text{ mV}$ at $+25^\circ\text{C}$ )
Temperature range (Basic circuit)	$+2^\circ\text{C}$ to $+150^\circ\text{C}$
Temperature range (Full range with pull-down)	$-55^\circ\text{C}$ to $+150^\circ\text{C}$
Accuracy	$\pm 0.5\text{ }^\circ\text{C}$ at $+25^\circ\text{C}$ ( $\pm 0.25\text{ }^\circ\text{C}$ for LM35A)
Quiescent current	60 µA typical
Package options	TO-92 (3-pin plastic), SOIC-8, TO-46 (metal can)

Pinout

Standard TO-92 Plastic Package (Flat side facing you, pins down)

text

        ┌─────────┐
        │  LM35   │
        └─────────┘
          │  │  │
          1  2  3

Pin	Name	Type	Description
1	`VCC`	Power	Supply voltage (+4.0 V to +30.0 V DC)
2	`VOUT`	Analog Output	Voltage output linearly proportional to temperature ( $10\text{ mV/}^\circ\text{C}$ )
3	`GND`	Power	Ground (0 V)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Supply Voltage	$V_{S}$	4.0	5.0	30.0	V	DC
Output Scale Factor	$S$	9.9	10.0	10.1	mV/°C	$+25^\circ\text{C}$
Accuracy (LM35D)	$\Delta T$	-1.5	$\pm 0.6$	+1.5	°C	At $+25^\circ\text{C}$
Non-Linearity	$NL$	—	$\pm 0.2$	$\pm 0.5$	°C	Over full temperature range
Quiescent Current	$I_{S}$	43	56	133	µA	$V_{S} = 5.0\text{ V}$
Self-Heating in Air	$\Delta T_{self}$	—	0.08	0.1	°C	Still air, TO-92

Temperature Conversion Formula

Converting the raw analog-to-digital converter (ADC) voltage reading ( $V_{OUT}$ in Volts) to temperature ( $T$ in °C):

$T\text{ }(^\circ\text{C}) = \frac{V_{OUT}\text{ (in Volts)}}{0.010\text{ V/}^\circ\text{C}} = V_{OUT}\text{ (in mV)} \times 0.1$

With a 10-bit ADC ( $1024$ steps) using a $5.0\text{ V}$ reference voltage ( $V_{REF} = 5000\text{ mV}$ ):

$T\text{ }(^\circ\text{C}) = \left(\frac{\text{ADC Output} \times 5000\text{ mV}}{1024}\right) \times \frac{1}{10\text{ mV/}^\circ\text{C}} = \frac{\text{ADC Output} \times 500}{1024}$

Wiring

LM35 TO-92 Pin	→	Microcontroller (Arduino Uno / ESP32)
1 (`VCC`)		`5V` (or 4V–30V power supply)
2 (`VOUT`)		Analog Input Pin `A0` (or ADC input)
3 (`GND`)		`GND`

Warning

Minimal Supply Voltage Requirement: The LM35 requires a minimum supply voltage of 4.0 V DC. Powering an LM35 directly from a 3.3V rail will cause reading compression and non-linear errors above $+25^\circ\text{C}$ . Use a TMP36 for native 2.7V–3.3V low-voltage applications.

Common mistakes

Powering from 3.3V rail: Supplying 3.3V to VCC falls below the 4.0 V minimum operating threshold.
Reverse polarity connection: Connecting VCC and GND backwards causes the LM35 to rapidly overheat and destroy the silicon die within seconds.
Measuring sub-zero temperatures without negative bias: In a basic single-supply circuit ( $V_{OUT}$ referenced to GND), the LM35 cannot output negative voltages. To measure temperatures below $0^\circ\text{C}$ , connect a pull-down resistor from VOUT to a negative voltage rail (or use two diodes).

Notes

Using a $1.1\text{ V}$ internal ADC reference voltage on Arduino Uno ( $V_{REF} = 1.1\text{ V}$ ) increases temperature resolution from $0.488\text{ }^\circ\text{C/count}$ to $0.107\text{ }^\circ\text{C/count}$ .