LM73 | GUILCOR SENSORS

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 ?

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 (12-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.

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.

Main registers (7-bit address: 0x48 → 0x4B)

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 Reading Example (pseudo-code)

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

Typical integration diagram

+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.

Quick configuration example (CONFIG register)

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