Data Sheet

high; this shuts down the regulator and causes the power mux to fall back to USB power. For example, this could

allow a battery-powered device to turn off the regulator and avoid draining its battery while it is connected to a

computer.

The input voltage range of the regulator depends on the particular version of the A-Star 32U4 Mini:

• ULV: 0.5 V to 5.5 V (see Section 4.2 for regulator details)

• LV: 2.7 V to 11.8 V (see Section 4.3 for regulator details)

• SV: 5 V to 36 V (see Section 4.4 for regulator details)

Reverse-protected power inputs: The BAT+ and BAT- pins are power inputs with reverse-voltage protection. These

are the recommended pins to use when connecting an external power supply because they allow the A-Star’s reverse-

voltage protection circuit to help prevent it from being damaged by accidentally-reversed power connections.

VIN power output (or alternative input): When power is supplied through the BAT pins, the VIN pin can be used

as an output to supply reverse-protected power to other devices. Alternatively, the external supply can be connected

directly between VIN and GND, bypassing the reverse-voltage protection.

5V power output: This pin provides access to the board’s 5 V supply, which comes from either the USB 5 V bus

voltage or the onboard switching regulator, depending on which power sources are connected and enabled. Note that

some of the available current on the 5 V line is used by the board itself (typically about 30 mA) or used to provide

current for the GPIO pins or 3.3 V power output (see below).

3V3 power output: This pin gives access to the output of the internal 3.3 V regulator inside the ATmega32U4.

The microcontroller uses this regulated voltage for USB signaling, but up to about 50 mA is available for powering

external circuits or devices.

When the A-Star 32U4 Mini is being powered through VIN, the sum of the 5V output current, 3V3 output current,

GPIO output current, and current used by the board itself should not exceed the maximum current that the regulator

can provide; see the following sections for details about the regulator on each version.

4. A-Star 32U4 Mini Page 13 of 47