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Hawk - Under Voltage Lockout

When power to the device is insufficient to power the device correctly, (i.e. the battery goes flat), the device will enter an Under Voltage Lock Out (UVLO) state to prevent reboot loops, and damage to any components. 

The UVLO behaviour has been designed to cater for different power setups e.g. 

  • Battery + Solar Panel
  • Battery + stable mains power
  • Battery Only

Summary of behaviour:

  1. When the battery goes flat, the device resets and enters the UVLO state
  2. It will wait for external power to be detected
  3. Once detected, it will spend around 30s to determine if the external power is stable
    1. If stable, exit the UVLO state and begin normal operation. 
    2. If unstable, attempt to charge the battery for 15min 
    3. After charging, check the battery voltage. *If the voltage is over 3.7V, exit UVLO
  4. Otherwise, repeat from step 2

The above ensures that on top of avoiding reboot loops, we also avoid entering/exiting UVLO repeatedly in the case of a solar panel outputting a low current trying to charge a flat battery. 

Some points to note when bench testing/provisioning the Hawk

  1. To avoid getting stuck in the UVLO state use a well charged battery (3.8V+), or connect a stable external power source (e.g. 12V bench power supply)
  2. You can exit the UVLO state by pressing the button on the board for around 200ms. The LED will flash to indicate success.

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