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CC2540: Low-Power Mode Timing

Josh Reed
Prodigy 10 points
Part Number: CC2540

Our application is highly sensitive to current draw (non-rechargeable battery powered device) and we recently noticed some inconsistent current draw that we are hoping someone could help us understand/optimize.  

We are still using stack version 1.4.0 (from 2013) and I realize that this chip is “outdated” considering what is available now, but our design is locked and we need to work with what we have. 

What is the minimum time delay (timer value) required for the BLE Micro to go to low-power mode?

Should 2 milli-seconds timer be enough for the BLE Micro to go to sleep/low-power state consistently?

Note: We have observed that it goes to sleep few times with 3 milli-seconds, but not all the time. 2 milli-seconds has not allowed the Micro to go to sleep based on current draw waveforms

We are trying to determine what the proper operation should be and adjust our code appropriately

  • 0
    Guru 735455 points

    I suppose you can add GPO toggle in hal_sleep.c to measure the exact timing that device enters and leaves sleeping mode.

  • 0
    TI__Guru 57865 points

    Hi,

    We do not have that characterised but the following app note contains some traces that would indicate post-processing during connection events take around 1ms before going into sleep;

     

  • 0
    TI__Guru** 106705 points

    Hi Josh,

    As stated in the datasheet, 32 MHz crystal oscillator section, there is a 3 ms guard time between disabling and re-enabling the 32 MHz crystal oscillator. This means that for any sleep duration less than 3 ms, the device should not go to low power modes. Based on your observations I assume the BLE Stack has a built in mechanism to ensure this does not happen.

    Regards,
    Fredrik