TMP125 | GUILCOR SENSORS

TMP125
Temperature sensors

Digital temperature sensor with SPI-compatible interface, offering reliable and accurate measurements for industrial environments.

Maximum precision
+/- 1,0°K

Minimum temperature
-55°C

Maximum temperature
+125°C

Minimum dimensions
3 x 3 x 1

Response time

Fast

Drift

Low

Self-warming
Low

Price
Medium

What is a TMP125 sensor ?

The TMP125 is a 12-bit SPI digital temperature sensor developed by Texas Instruments.

It directly converts ambient temperature into digital data, without external components.

Compact, accurate, and fast, it is perfect for embedded systems, electronic boards, and industrial thermal monitoring.

Operating principle

The TMP125 measures temperature through an integrated diode whose voltage varies with temperature.

This voltage is converted by a 12-bit internal ADC and then transmitted via SPI.

The conversion is signed in two's complement (MSB = sign bit).

T(°C) = Value x 0,0625

Technical Specifications

Parameter	Typical value
Resolution	12 bits (0,0625 °C / LSB)
Measurement range	−55 → +125 °C
Precision	±1,0 K (typ.)
Interface	SPI (read-only)
Conversion time	120–160 ms
Max. SPI Frequency	5 MHz
Power supply voltage	2,7 → 5,5 V
Typical current	250 µA
Sleep mode	< 1 µA
Case	SOT-23-6
Annual drift	±0,2 K/year

Wiring Configuration

Brooch	Name	Function
1	CS	Chip Select (active low)
2	SO	SPI Output (MISO)
3	SCK	SPI Clock
4	V+	Power Supply (2.7–5.5 V)
5	GND	Mass
6	NC	Not connected

Self-warming

Almost zero thanks to an internal current < 250 µA.

The TMP125 can be placed directly in contact with a component to be monitored (MOSFET, CPU, PCB, etc.).

Application areas

⚙️ Thermal surveillance of electronic boards

🔋 Thermal management of batteries or DC/DC converters

🧠 Monitoring of microcontrollers, FPGAs, or ASICs

💡 Industrial or environmental instrumentation

🧱 Low-power embedded systems

Should I choose a TMP125 sensor ?

Strengths points

⚙️ Direct digital output
→ The TMP125 delivers a pre-converted and calibrated SPI value, without the need for an amplifier or linearization. A true “plug & measure.”
🎯 Stable accuracy and low drift
→ With an accuracy of ±1 K and a drift of less than ±0.2 K/year, it ensures lasting stability, even in critical systems.
💡 SOT-23 miniature format
→ Its ultra-compact size allows for direct integration with the components to be monitored, perfect for onboard thermal management.

Weaknesses points

🌡️ Limited measurement range
→ Limited to −55 → +125 °C, this sensor is not suitable for very high temperature environments (oven, extrusion, etc.).
🔋 Unidirectional communication
→ The SPI bus is read-only, with no command or dynamic configuration (unlike some modern I²C sensors).
💰 Little interest in multi-sensor systems
→ Each TMP125 requires its own CS line, which complicates the wiring when exceeding 2 or 3 sensors.

Useful information

Here is some useful information regarding the TMP125 sensors.

Resolution and precision

The TMP125 is a 12-bit signed digital temperature sensor with a fixed resolution of 0.0625 °C / LSB.

It directly converts the ambient temperature into digital data via an integrated diode and an onboard ADC.

Parameter	Typical value
Resolution	12 bits (0,0625 °C / LSB)
Measurement range	−55 → +125 °C
Precision	±1,0 K (−25 → +100 °C)
Annual drift	±0,2 K
Conversion time	120 → 160 ms
Power supply voltage	2,7 → 5,5 V
Consumption	250 µA typical
Interface	SPI (read-only)
Max. SPI Frequency	5 MHz

🔹 Notes:

Each conversion yields a signed value in 12 bits (2’s complement).
No external calibration required.
The internal noise is less than 0.05 °C RMS.

Application Example – SPI Reading

During a 16-bit SPI read, the 12 most significant bits contain the temperature.

The value is signed, with the MSB (bit 15) indicating the sign (0 = positive, 1 = negative).

🔹 SPI word structure (16 bits)

Bit(s)	Name	Description
[15]	Sign	0 = + / 1 = −
[14 → 3]	Temperature (12 bits)	Value × 0.0625 °C
[2 → 0]	Reserved	0

🔹 Conversion equation

T (°C) = Valeur₁₂b × 0,0625

Practical example:

SPI reading → 0x07D0

0x07D0 = 2000₁₀

T = 2000 × 0,0625 = 125,0 °C

✅ Measured temperature = 125 °C

Integration into an electronic system

The TMP125 easily integrates with any microcontroller that has an SPI interface (Arduino, STM32, ESP32, Raspberry Pi…).

It only requires 3 active lines: CS, SCK, and SO (MISO).

🔹 Typical components

Component	Function
TMP125	Digital temperature sensor SPI
Microcontroller (3.3 or 5 V)	Master SPI
Pull-up resistances (optional)	CS stability and clock
Supply	2,7–5,5 V
100 nF capacitor	Decoupling near the sensor

🔹 Functional diagram (ASCII)

        +3.3V / +5V
             │
         [TMP125]
             │
        SO ────► MISO (MCU)
        SCK ◄─── CLK  (MCU)
        CS  ◄─── GPIO (MCU)
        GND ───── GND

💡 Multiple TMP125 devices can be connected on the same SPI bus, each with its own CS line.

🔹 Operating Principle

1️⃣ The microcontroller pulls CS low to initiate a read.

2️⃣ The TMP125 sends 16 bits: temperature on 12 bits + reserved bits.

3️⃣ The MCU calculates the temperature: T=value×0.0625T = value × 0.0625T=value×0.0625.

4️⃣ The sensor returns to automatic sleep mode to save energy.

Practical advantage

Advantage	Description
🧠 Direct digital lecture	Integrated conversion and linearization
⚙️ Universal SPI Interface	Easy to interface, quick reading
🎯 Good accuracy ±1 K	Sufficient for industrial monitoring
🔋 Low consumption (250 µA)	Perfect for battery systems
💡 Miniature and reliable	Easy integration on electronic board
🔧 No calibration required	Data ready to use