SI7055-EVB Silicon Labs

AN1026: Si70xx Temperature Sensor De- signer s Guide This designer s guide describes the Si70xx family of temperature KEY POINTS sensor products in a variety of different applications. Thermal Mass and Thermal Resistance The Si7050/1/3/4/5 temperature sensors are supplied in a 3 x 3 mm 6 pin QFN package Thermal Model for a Sensor on a Paddle and support the supply voltage range of 1.9 to 3.6 V. The Si7057/8/9 are supplied in a 6- Compensating for Heating and Thermal pin 2 x 2 mm package and support the the supply range of 1.67 to 1.98 V. Refer to the Response Time for Ambient Measurements data sheets for detailed pin descriptions, register summaries, and timing details. Core Body Temperature Measurement Some information in this designers guide is also applicable to the Si70xx temperature and humidity sensors. SeeAN607: Si70xx Humidity and Temperature Sensor Design- er s Guid for more information. The architecture of the Si70xx temperature sensors is shown in the general block dia- gram below: silabs.com Smart. Connected. Energy-friendly. Rev. 0.1 AN1026: Si70xx Temperature Sensor Designer s Guide Introduction 1. Introduction The Si70xx temperature sensors work by measuring the Vbe of an on chip transistor at two currents in a precise ratio to measure tem- perature. The resulting voltage is digitized, calibrated and linearized such that after conversion the temperature can be easily calcula- ted. Thus the temperature being measured is the temperature of the die within the Si70xx package. This die is mounted on a metal lead frame. It is useful to think of the leadframe as the thermal input to the die since the thermal resistance from the paddle to die is quite low (a few C/W) while the thermal resistance through the top of the package is quite high (over 1000 C/watt for convective heat transfer). Depending on part number and conversion time, the Si70xx parts will measure the temperature of the sensing transistor in a time win- dow of less than 1 ms up to about 10 ms. As temperature is not a quantity that can easily change quickly, this measurement can be 2 considered to be an instantaneous snap shot of the die temperature that is taken once the I C command to measure temperature has completed. silabs.com Smart. Connected. Energy-friendly. Rev. 0.1 1