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attach the power supply to either J14 or J17 and place a shorting block in the EXT position of J15. Be sure to
observe correct polarity when connecting a power supply to J14, as a reversed connection could damage the
board. To operate the WF32 as a USB powered device from the USB OTG connector (J12) place a shorting block on
the USB position of J15. This will normally only be done when running a sketch on the board that programs it to
operate as a USB device. The power supply section in the WF32 provides two voltage regulators, a 3.3V regulator
and a 5V regulator. All systems on the WF32 board itself operate at 3.3V and are powered by the 3.3V regulator.
The 5V regulator is used to provide power for external circuits, such as shields, that require 5V for operation. The
5V regulator can be completely disabled if it is not needed for a given application.
The WF32 board is designed for low power operation and efficient use of battery power, as such a switch mode
voltage regulator is used for the 3.3V power supply. This switch mode regulator is made up of a Microchip
MCP16301 and associated circuitry. It can operate on input voltages from 4V to 30V with up to 96% efficiency, and
is rated for 600mA total current output. The MCP16301 has internal short circuit protection and thermal
protection. The 3.3V regulator takes its input from the unregulated power bus, VU, and produces its output on the
VCC3V3 power bus. The VCC3V3 bus provides power to all on-board systems and is available at the shield power
connector (J3) to provide 3.3V power to external circuitry, such as shields.
The 5V regulator section provides a low dropout linear regulator. No circuitry on the WF32 board uses the 5V
supply. It is provided for powering external circuitry that needs a 5V power supply. This voltage regulator uses an
On Semiconductor NCP1117LP. The NCP1117LP is rated for an output current of 1A. The dropout voltage of the
NCP1117LP is a maximum of 1.4V at 1A output current. The maximum input voltage of the NCP1117LP is 18V. The
recommended maximum operating voltage is 15V.
The input voltage to the 5V regulator section is taken from the VU bus, and the output is placed on the VCC5V0
power bus.
There is a reverse polarity protection diode in the external power supply circuit. Considering the diode drop plus
the forward drop across the regulator, the minimum input voltage to the regulator should be 7V to produce a
reliable 5V output.
For input voltages above 9V, the regulator will get extremely hot when drawing high currents. The NCP1117LP has
output short circuit protection and internal thermal protection and will shut down automatically to prevent
damage.
The 5V regulator section actually provides four 5V power options:
1) 5V regulator completely disabled and no 5V power available;
2) 5V regulator bypassed and 5V provided from an external 5V power supply, such as USB;
3) on-board 5V regulator used to provide 5V power;
4) External 5V regulator used to regulate VU and provide 5V power.
Jumper block J16 is used to select these various options and the following diagrams describe the use of J16:
This diagram shows the arrangement of the signals on J16:
LDO OutLDO In
VU 5V0
GNDEN Ext
(11 pages)
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