3.3 Low-Power Operation

To achieve the lowest power consumption of the board, the following considerations must be taken:
  • Set the MCP9844 in Shutdown mode
    • Set bit 8 (SHDN) in the 16-bit CONFIG register (address 0x01)
  • Set the BMA253 in Deep Suspend mode
    • Set bit 5 (deep suspend) in the 8-bit PMU_LPW register (address 0x11)
  • Set the RN4870 in Sleep mode
    • Set the RX_IND pin high (PD2 on the ATmega3208)
    • Send the "O,0\r" command to the RN4870
  • Set unused ATmega3208 I/O pins as input and disable the digital input buffer
Important: USART pins PF0 and PF1 are connected directly to the on-board debugger. It is important to tri-state the USART pins when the board is powered from a CR2032 battery to prevent powering the debugger through its I/O pins. Doing so will increase the power consumption and cause undefined behavior from the on-board debugger.
Info: The load switch U300 in the power MUX can leak up to 1 μA when the board is powered from a battery. By modifying the board and removing resistor R303 (0Ω), U300 can be disconnected. Be warned that a board modified this way can no longer be powered from USB, and consequently, neither programmed nor debugged using the on-board debugger until the 0Ω resistor is reconnected.