Data Sheet

ams Datasheet Page 9
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CCS811 − Detailed Description
Conditioning Period (Run-In)
After early-life (Burn-In) period is complete the conditioning
period is the time required to achieve good sensor stability
before measuring VOCs after long idle period.
After writing to MEAS_MODE to configure the sensor in mode
1-4, run CCS811 for 20 minutes, before accurate readings are
generated.
The conditioning period must also be observed before writing
to the BASELINE register.
eCO
2
The equivalent CO
2
(eCO
2
) output range for CCS811 is from
400ppm to 8192ppm. Values outside this range are clipped.
TVOC
The Total Volatile Organic Compound (TVOC) output range for
CCS811 is from 0ppb to 1187ppb. Values outside this range are
clipped.
This is calibrated to a typical TVOC mixture in an indoor
environment. If the ratio of compounds in the environment is
significantly different the TVOC output will be affected as some
VOC compounds will have greater or lesser effect on the sensor.
Temperature and Humidity Compensation
If an external sensor is available this information can be written
to CCS811 so that they will be used to compensate gas readings
due to temperature and humidity changes. Refer to the
ENV_DATA (Environment Data) Register (0x05).
Interrupt and Interrupt on Threshold
At the end of each measurement cycle (250ms, 1s, 10s, 60s) a
flag is set and optionally interrupt (nINT) pin asserted. Refer to
the MEAS_MODE (Measurement and Conditions) Register
(0x01). The user can choose to only assert nINT if the eCO
2
value
changes into a different range set by register values. Refer to the
THRESHOLDS Register (0x10).
Optional NTC Circuit (AUX)
CCS811 supports an external interface for connecting a
negative thermal coefficient (NTC) thermistor to provide a cost
effective and power efficient means of calculating the local
ambient temperature.
The thermistor enables the application to determine the
ambient temperature in the location where the CCS811 is
deployed. This temperature can subsequently be used for
environmental compensation on the CCS811 MOX gas sensor.