TCN75A | GUILCOR SENSORS

TCN75A
Temperature sensors

Cost-effective I²C temperature sensor compatible with LM75, suitable for basic thermal management applications.

Measurement range
-40 / 125°C

Temperature accuracy
+/- 1,0°K

Resolution (Rh and T°)
9 to 12 bits

Power supply voltage
2,7 → 5,5V

Conversion time
240 ms

Typical current
250 µA(active)

I²C Speed
0x48

Price
Low

What is a TCN75A sensor ?

The TCN75A is a digital temperature sensor with an I²C interface, fully calibrated and linear, developed by Microchip Technology.

It is a modern equivalent of the LM75, widely used in electronic boards, servers, power supplies, embedded systems, and consumer products.

It offers good accuracy, stability, and SMBus compatibility, all in a compact and cost-effective format.

Operating principle

The TCN75A integrates:

a silicon junction temperature sensor,
a 12-bit ADC converter,
a configuration EEPROM memory,
and a programmable alert output (ALERT pin).

The data is transmitted in the form of a signed word (MSB + LSB) according to the formula:

T(°C) = Signed codex / 16

(in 12-bit mode, or 0.0625 °C per LSB)

Example of conversion

Signed hex value	Temperature (°C)
0x0000	0,0
0x0100	1,0
0x1900	25,0
0x3200	50,0
0x6400	100,0

💡 Identical format to the LM75 – the drivers are interchangeable.

Principle diagram (I²C connection)

+3.3V
 │
[TCN75A]
 │ SDA ─────────┐
 │ SCL ─────────┤── [I²C Microcontroller]
 │ A0–A2 ───────┘ (address configuration)
 │ ALERT ───────┐ (alert exit)
 │ GND

💡 I²C Address: 0x48 → 0x4F according to A0–A2.

Application areas

💻 Thermal monitoring of CPU / GPU / electronic boards

⚙️ Embedded systems and simple regulation

🔋 Thermal protection in power supplies

🧠 Low-cost IoT projects

🏠 Basic digital thermometers

Should I choose a TCN75A sensor ?

Strengths points

💰 Ultra economical and proven
→ One of the most affordable I²C sensors on the market.
⚙️ Compatible LM75→ Same protocol, same registers — direct replacement without code modification.
🔋 Low consumption
→ Perfect for battery-operated systems or long-term standby.
📡 Configurable address
- → Up to 8 sensors on the same I²C bus.

Weaknesses points

🎯 Limited precision
→ ±1 K — sufficient for monitoring, insufficient for precision measurements.
📏 Variable resolution
→ From 9 to 12 bits — to be adjusted as needed (and the conversion time).
🌡️ No dynamic calibration
→ A possible long-term drift if exposed to high temperatures for an extended period.

Useful information

Here is some useful information regarding the TCN75A sensors.

Main Registers (I²C)

Adress (hex)	Name	Function
0x00	Temperature Register	Temperature data (2 bytes)
0x01	Configuration	Resolution, mode, polarity
0x02	T_HYST	Hysteresis threshold
0x03	T_OS	Trigger threshold
0x04	Product ID	Component ID
0xFF	Shutdown / One-shot	Energy-saving mode

I²C Reading Example (pseudo-code)

i2c_start();
i2c_write(0x48 << 1);
i2c_write(0x00);
i2c_start();
i2c_write((0x48 << 1) | 1);
MSB = i2c_read_ack();
LSB = i2c_read_nack();
i2c_stop();

raw = (MSB << 8) | LSB;
if (raw & 0x8000) raw -= 65536;
temp = raw / 16.0; // 0.0625°C per LSB

✅ Example :

MSB = 0x19, LSB = 0x00 → (0x1900 / 16) = 25,0 °C

Typical integration diagram

3.3V ───────────┐ │ [TCN75A] │ SDA ───────┐ │ SCL ───────┤── MCU (Arduino, STM32, ESP32…) │ ALERT ─────┘ (heat alert) │ GND

💡 The SDA/SCL pull-up resistors (4.7–10 kΩ) are essential.

Configuration Register (0x03)

Bit	Name	Description
[7]	One-shot	1 = unique measure
[6]	Resolution bit1	Resolution setting
[5]	Resolution bit0	9 to 12 bits
[4]	Fault queue	1 to 4 samples before alert
[1]	Mode	0 = continue / 1 = standby
[0]	Polarity	Pin polarity ALERT