Connectors, Power – Pololu A-Star 32U4 User Manual
Page 10
The
red
LED is connected to the pin labeled RXL, or PB0, and lights when the pin is driven low. While the board is
running the A-Star 32U4 Bootloader or a program compiled in the Arduino environment, it will flash this LED when
it is receiving data via the USB connection.
Connectors
The A-Star 32U4 includes a USB Micro-B connector that can be used to connect to a computer’s USB port via a
(not included). The USB connection can be used to transmit
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 dot and has
an octagonal shape.
Power
The A-Star 32U4 Mini can either be powered directly from the USB 5 V supply or from an external voltage source,
which is regulated to 5 V by its onboard switching regulator.
The board’s power selection circuit uses the
from
Texas Instruments to choose whether its 5 V supply is sourced from USB or an external supply via the regulator,
allowing both sources to be connected at the same time and enabling the A-Star to safely and seamlessly transition
between them. The TPS2113A is configured to select external power unless the regulator output falls below about
4.5 V. If this happens, it will select the higher of the two sources, which will typically be the USB 5 V bus voltage if
the A* is connected to USB. The currently selected source is indicated by the STAT pin in the middle of the board;
this pin is an open-drain output that is low if the external power source is selected and high-impedance if the USB
supply is selected. The current limit of the TPS2113A is set to about 1.9 A. For more information about the power
multiplexer, see the
(1MB pdf).
In some situations, it might be undesirable for the A-Star 32U4 Mini to draw power from an external source when it
is connected to USB. If this is the case, the regulator can be disabled by driving the regulator shutdown pin, SHDN,
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
for regulator details)
• LV: 2.7 V to 11.8 V (see
for regulator details)
• SV: 5 V to 36 V (see
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
Pololu A-Star 32U4 User’s Guide
© 2001–2014 Pololu Corporation
4. A-Star 32U4 Mini
Page 10 of 30