SI7021-A20 Datasheet, PDF (13/36 Pages) Silicon Laboratories – IC HUMIDITY AND TEMPERATURE SENSOR

4. Functional Description
Si7021-A20
Figure 5. Si7021 Block Diagram
The Si7021 is a digital relative humidity and temperature sensor that integrates temperature and humidity sensor
elements, an analog-to-digital converter, signal processing, calibration, polynomial non-linearity correction, and an
I²C interface all in a single chip. The Si7021 is individually factory-calibrated for both temperature and humidity,
with the calibration data stored in on-chip non-volatile memory. This ensures that the sensor is fully
interchangeable, with no recalibration or changes to software required. Patented use of industry-standard CMOS
and low-K dielectrics as a sensor enables the Si7021 to achieve excellent long term stability and immunity to
contaminants with low drift and hysteresis. The Si7021 offers a low-power, high-accuracy, calibrated and stable
solution ideal for a wide range of temperature, humidity, and dew-point applications including medical and
instrumentation, high-reliability automotive and industrial systems, and cost-sensitive consumer electronics.
While the Si7021 is largely a conventional mixed-signal CMOS integrated circuit, relative humidity sensors in
general and those based on capacitive sensing using polymeric dielectrics have unique application and use
requirements that are not common to conventional (non-sensor) ICs. Chief among those are:
The need to protect the sensor during board assembly, i.e., solder reflow, and the need to subsequently
rehydrate the sensor.
The need to protect the senor from damage or contamination during the product life-cycle.
The impact of prolonged exposure to extremes of temperature and/or humidity and their potential effect on
sensor accuracy.
The effects of humidity sensor “memory”.
Each of these items is discussed in more detail in the following sections.
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