AT%SLEEP=n power consumption

Werner Almesberger werner at
Mon Oct 20 01:21:32 CEST 2008

I order to evaluate the impact of the AT%SLEEP=2 work-around, Joerg
asked me to measure how the sleep mode affects the current drawn by
the system.

Test setup:

- device is idle but (for convenience) not suspended
- GSM is active and has registered with the network (AT+CFUN=1,
- the test setup does not suffer from #1024
- power is supplied to the battery terminals from a lab power supply
  set to 4.0V
- USB is not connected

Battery current of the whole system in mA. Values are from measurements
averaged over about 15 minutes each:

at%sleep=       avg     min     max     samples
4                96.0    91.6   198.0   20006
3                98.4    91.6   214.6   21432
2               102.2    97.6   209.3   21428
1               104.0   101.9   197.2   21352
0               120.3   118.8   213.0   21452

Integration period is one power line cycle (20ms). There are transients
much faster than 50Hz. E.g., sampling at 2.5kHz finds more noise but
does not change the difference in the averaged value:

at%sleep=       avg     min     max     samples
4                95.1    63.1   242.5   210207
3                97.1    62.8   242.9   215460
2               101.4    68.7   243.4   208230

Note that this is an idle but not suspended system, hence the large
minimum current.

So the difference between sleep=2 and sleep=4 is about 6mA. Joerg
mentioned that the idle current of the GSM subsystem should be 4mA,
so this would be an increase to 250%.

Andy, you once measured the power consumption when the overall system
is perfectly suspended. Do you still remember how much it was ?

- Werner

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