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 LM73 
 Temperature sensors 

Compact digital temperature sensor with fast response time, designed for embedded and low-power applications.

 Maximum precision
+/- 1,0°K

 Measurement range
-40 / 15°C

 Resolution
11 à 14 bits

 Power supply voltage
2,65 → 3,6V

Conversion speed

20 to 120mS

I2C adress
0 x 48

 Typical current
300µA(active)

 Price
Medium

What is a LM73 sensor ?Operating principleTemperature curve / numerical value (12-bit resolution)Principle diagram (I2C connection)Application areas

What is a LM73 sensor ?

The LM73 is a digital temperature sensor with I²C/SMBus output, developed by Texas Instruments (formerly National Semiconductor).

It succeeds the LM75 by providing:

  • a resolution of up to 14 bits (compared to 9 bits for the LM75),
  • better accuracy,
  • an adjustable conversion time,
  • and an advanced configuration register.

It is an excellent compromise between simplicity and performance, ideal for demanding embedded applications without going up to metrological precision models (like the TMP117).

Operating principle

The LM73 uses an integrated thermal sensor coupled with a 14-bit ΔΣ (Delta-Sigma) converter.

The measurement is stored in an internal register and transmitted via the I²C bus.

Each bit corresponds to 0.03125 °C in 14-bit mode.

​T(°C) = Binare code x 0,03125

💡 Selectable resolution: 11, 12, 13, or 14 bits depending on needs (accuracy vs speed).

Temperature curve / numerical value (14-bit resolution)

Temperature (°C)
 Numerical value (hex)

Binary output (12bits)

-40

 0xF600

1111 0110 0000 0000
0 0x0000

0000 0000 0000 0000

25

0x0800

0000 1000 0000 0000

85 0x1500

0001 0101 0000 0000

125

0x1F00

0001 1111 0000 0000

🧮 1 LSB = 0.03125 °C → 32 values per degree Celsius.

Principle diagram (I²C connection)

+3.3V
 │
[LM73]
 │ SDA ─────────┐
 │ SCL ─────────┤── [I²C Microcontroller]
 │ ALERT/OS ────┘
 │ GND

💡 The LM73 can coexist with other I²C sensors thanks to its two address pins (A0–A1).

Application areas

🧠 Embedded cards and IoT

⚙️ Industrial temperature monitoring

🧪 Laboratory electronics and data loggers

🔋 Thermal management of batteries / power supplies



Should I choose a LM73 sensor ?

Strengths points

  • 🎯 Better resolution than the LM75
         → With its 14 bits, it detects variations of 0.03 °C, compared to 0.5 °C for the LM75.
  • 🧠 Flexible configuration → Adjustable speed and resolution: perfect for balancing precision and responsiveness according to the application.
  • 📡 Total SMBus compatibility
         →Works equally well with a microcontroller, a motherboard controller, or an industrial PC.
LM73 sensors

Weaknesses points

  • 🌡️ Moderate accuracy compared to TMP117
         → Even with more bits, the accuracy remains limited to ±1 K typical.
  • ⚙️ No built-in calibration
         → The errors due to assembly or thermal radiation must be compensated for by software.
  • 💸 Price slightly higher than the LM75
         → But justified by its increased resolution and flexibility.

Useful information

Here is some useful information regarding the LM73 sensors.

Adress Registry Name
 Function
0x00 Temperature Register Measurement result (14 signed bits)
0x01 Configuration Register Definition of mode, resolution, and conversion
0x04 T_Hyst Register Low threshold for alert
0x05 T_Limit Register High threshold for alert
0x07 ID Register Component ID and revision 
i2c_start();
i2c_write(0x48 << 1);      // Address LM73 (writing)
i2c_write(0x00);           // Temperature log
i2c_start();
i2c_write((0x48 << 1) | 1);
MSB = i2c_read_ack();
LSB = i2c_read_nack();
i2c_stop();

raw = (MSB << 8) | LSB;
temp = (raw >> 2) * 0.03125; // 14-bit conversion (2 useless bits)

✅ Example:

MSB = 0x08, LSB = 0x00

→ (0x0800 >> 2) × 0.03125 = 32 × 0.03125 = 25.0 °C

+3.3V ───────────┐
                 │
                [LM73]
                 │ SDA ───────┐
                 │ SCL ───────┤── MCU I²C (Arduino, STM32, ESP32…)
                 │ ALERT ─────┘
                 │ GND

💡 Pull-up resistors (4.7 kΩ typical) are required on SDA and SCL.

Bit Name
 Description
[7:6] Resolution 00=11 bits, 01=12 bits, 10=13 bits, 11=14 bits
[5:3] Conversion Rate 000=1 Hz / 111=32 Hz
[2] One-shot Unique conversion
[1:0] Mode 00=Normal / 01=Shutdown / 10=Comparator / 11=Interrupt
Temperature (°C) Max error (K)
−40 ±1,5
0 ±1,0
50 ±0,8
100 ±1,0
125 ±1,5
💡 The LM73 offers an excellent balance between precision, responsiveness, and simplicity — a solid choice for embedded applications.

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