Power – Pololu A-Star 32U4 User Manual
Page 6
and receive data from the computer, and a preloaded USB bootloader makes it possible to program the board over
USB. The USB connection can also provide power to the A-Star.
The board also has a 6-pin ISP header that allows it to be programmed with an external programmer, such as our
Pin 1 of the header is indicated with a small white dot and
has an octagonal shape. Three of the pins on this header can be used as an SPI interface or as general-purpose digital
I/O, as shown in the pinout diagram. In the Arduino environment, you can refer to these three pins using either their
pin numbers or the names of their SPI functions (which are defined as aliases); for example,
digitalRead(15)
and
digitalRead(SCK)
are equivalent.
Power
The A-Star 32U4 Micro can either be powered directly from the USB 5 V supply or from a separate source on the
VIN pin. The board features a power selection circuit that allows both USB and VIN to be connected at the same
time; if this is done, the A-Star will draw power from VIN.
USB power input: The A-Star can be powered from the USB 5 V bus voltage (VBUS) if it is connected to a USB
cable. It will draw power from USB only if VIN is disconnected. A resettable PTC fuse on VBUS makes it less likely
for the A-Star (and the connected computer or other device) to be damaged if too much current is drawn from the
USB connection.
VIN power input: The A-Star can be powered from VIN if you connect a 5.5 V to 15 V power supply (such as a
battery or wall power adapter) to the VIN and GND pins, with the positive terminal connected to VIN.
When powering the A-Star 32U4 Micro from VIN, a minimum voltage of 5.5 V is required to ensure that
the board’s 5 V supply is stable. Even if power is being provided to the A-Star via USB, connecting a
voltage higher than 0 V but lower than 5.5 V to VIN is not recommended, as this can interfere with the
power selection circuit and cause the 5 V line to drop (potentially triggering a brown-out reset).
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 a low-dropout (LDO) regulator on VIN, depending on which power source is connected. The regulator can
supply up to 100 mA, although some of this is used by the board itself (typically about 25 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 Micro 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 100 mA that the regulator can provide.
Pololu A-Star 32U4 User’s Guide
© 2001–2014 Pololu Corporation
3. A-Star 32U4 Micro
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