Ultra-low-power temperature sensors maintain accuracy

January 13, 2015 // By Graham Prophet
Silicon Labs’ Si705x sensor family offers accuracy across its full operating temperature range with high levels of power efficiency.

The sensors consume 195 nA (typical average current) when sampled once per second, which minimises self-heating and enables multi-year coin-cell battery operation. Unlike traditional digital temperature sensors, the Si705x devices maintain their accuracy across the full operating temperature and voltage ranges and offer four accuracy levels up to ±0.3 °C. The sensors are suitable for HVAC, white goods, computer equipment, asset tracking, cold chain storage, industrial control and medical equipment. AEC-Q100-qualified versions are also available for automotive applications.

Traditional approaches to temperature sensing that use thermistors or embedded MCU temperature sensors suffer from poor accuracy and higher power consumption. Although improved accuracy can be achieved through end-of-line calibration, this technique presents additional manufacturing costs and challenges while accuracy is still susceptible to variations in power supply voltage. The Si705x sensors' signal processing technology provides stable temperature accuracy over the entire operating voltage and temperature ranges without the need for costly end-of-line production calibration. The integrated low-power analogue design delivers an optimal price/performance solution with up to 35 times better power efficiency than competing temperature sensor products.

In a 3 x 3 mm DFN package, the Si705x sensors feature an I²C interface for easy configuration. Each device provides up to 14-bit temperature resolution for high-precision measurement, and the -40 to +125 °C temperature range is suitable for consumer, industrial and automotive applications. With a 1.9V minimum power supply voltage, the Si705x sensors can be connected directly to a battery without the need for an external voltage regulator.

The Si705x temperature sensors are pin-compatible and software-compatible with Silicon Labs’ Si70xx RH and temperature sensor family. This compatibility enables existing RH sensor designs and software to be reused easily for temperature-only applications. Si705x pricing begins at $0.61 (10,000). USB dongle evaluation kits are priced at $49 and are supported by a Windows-based GUI that simplifies control of the Si705x sensors and temperature measurements. A variety of source code and driver examples is available