User Manual

Page 10 ams Datasheet
Document Feedback [v1-06] 2019-Feb-07
CCS811 − Detailed Description
Power States
The previous diagram showed that when the CCS811 is
powered On it can be in several functional states (e.g. App with
Mode1s). Orthogonal to this, when the CCS811 is On, it can be
in several power states. The diagram below illustrates the power
behavior.
Figure 10:
CCS811 Power States
As long as the CCS811 has work to do, for example, handling
I
2
C transactions from the master, executing a measurement or
running algorithms to convert measurement to eCO
2
/eTVOC,
the CCS811 is Busy. When measurements are enabled a timer is
running (which expires every 1, 10, 60 or 0.25 seconds), but
running a timer does not count as work.
When there is no work to do, the power state transitions from
Busy to either Idle or Sleep, depending on the state of the nWAKE
pin. With nWAKE high, the master requests Sleep mode, with
nWAKE low, the CCS811 stays Wake but Idle.
In Idle mode, work can appear, either an I
2
C transaction from
the host, or the timer expires, triggering a measurement
(followed by an algorithm step).
In Sleep mode the CCS811 is not ready to handle I
2
C
transactions. The master should first pull nWAKE low, this
causes the CCS811 to transition to Wake (Idle). A timer could be
running, when it expires, it also causes the CCS811 to transition
to Wake, but as Busy.
On
Wake
Idle
Busy
on no-work
if nWAKE=0
if nWAKE=1
Sleep
on falling nWAKE
on timer-expire
on work
[I2C transaction,
measuring, algorithm]
[nWAKE=0]
Off
power on
power off
[nWAKE=1,
no work,
a timer might
be running]
nRESET pulsed