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No separate connectors for SPI host connections are provided as there is no standard connector or pinout,
but the signals are available on the pin headers and pads on the prototyping area edge for easy soldering of a
connector with a custom pinout.
3.7 Board Power
DKWF121 can be powered by several sources.
Both USB connectors can be used as the power supply input
A two-pin header
The signal pin headers and prototyping area connections have power connections
Note: if the on-board WF121 module does not contain firmware that operates the native USB connection, the
module cannot request an increase to the USB default current limit of 100mA. Although not all USB host
systems implement it, the USB specification states that the host should limit the current output to 100mA
unless an increase is requested, and using the module with high transmit duty cycles may cause the USB host
to go into current limit, possibly causing the module to crash. It is preferred to power the board through the
USB/UART-converter connector, the converter chip will automatically request for an increased current limit.
The board contains a switch mode converter that converts the 5V input to the 3.3V supply required by the
module. The converter is specified for output currents up to 600mA, allowing up to 200mA to be drawn for
powering customer applications.
The module operates down to 2.7V, but the current measure output and USB host functionality require a
regulated 5V input. The header and the USB connectors also have series schottky diodes, increasing the
minimum input voltage slightly. The 5V power connections in the prototyping area and the associated pin
headers do not have series diodes. The diodes allow connection of a USB host together with a separate
power supply without risk of damage.
3.8 Current Measurement Point J13
Header J13 contains a jumper that connects the switch mode regulator to the module 3.3V supply pads. The
jumper can be removed and the average current consumption of the module can be measured with a
multimeter or a series resistor can be inserted for measuring the momentary current consumption of the
module with an oscilloscope. Note that for average consumption measurement of anything else besides sleep
current a fast RMS multimeter is needed due to the pulsed nature of the consumption.
Removing the jumper also allows separation of the module supply lines from the regulator output, for example
when using an external regulator to supply the 3.3V voltage to the module is desired.
3.9 VDD_PA Selection Header J7
WF121 has two power supply inputs, VDD_3.3V (VDD_3.3V_MOD line on the schematic) and VDD_PA. The
VDD_3.3V pad supplies the internal processor and has a voltage range of 2.3V to 3.6V. The VDD_PA pad
supplies the internal WiFi-circuitry through a switch mode converter and the WiFi power amplifier directly. The