Figure 3-3. Power Supply Block Diagram
USB
On-Board
Debugger
Power source
Power disconnect
Power consumer
Power converter
VUSB
MIC33050
(buck)
MUX
(MIC94050)
(MIC94165)
Power MUX
Battery
Holder
(CR2032)
VCC_P3V3
VBAT
VBAT_OUT
0Ω resistor
Target MCU
Peripherals
mBUS
RN4870
0Ω resistor
P3V3_ENABLE
Info:
On the mikroBUS socket, the +5V rail is powered from the USB port. Consequently, +5V will not be
available when the board is powered from a battery.
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.
3.4
Target Current Measurement
Power to the ATmega3208 and its peripherals is connected from the on-board power supply through a 0Ω resistor
(R301) in parallel with a 100-mil
Current sense
pin header footprint marked with “ISNS” in silkscreen (J301). To
Hardware User Guide
©
2020 Microchip Technology Inc.
User Guide
DS50002956A-page 14
