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Diffstat (limited to 'source/hardware/maple-mini.rst')
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1 files changed, 40 insertions, 11 deletions
diff --git a/source/hardware/maple-mini.rst b/source/hardware/maple-mini.rst index 986ab4b..58e394d 100644 --- a/source/hardware/maple-mini.rst +++ b/source/hardware/maple-mini.rst @@ -50,9 +50,40 @@ directly. .. warning:: The silkscreen on the Maple Mini suggests it will accept an input voltage up to 16 V. We recommend applying **no greater - than 12 V**. - - See :ref:`this erratum <maple-mini-vin>` for more information. + than 12 V**, and potentially even lower depending upon the current + draw requirements of the application. Please see :ref:`Power + Regulation on the Maple Mini <maple-mini-power-regulation>` for + more information. + +.. _maple-mini-power-regulation: + +Power Regulation on the Maple Mini +---------------------------------- + +Power regulation on the Maple is provided by two low dropout linear +voltage regulators. (The part is the MCP1703 from Microchip, in the +SOT-23A package. You can download the datasheet `here +<http://ww1.microchip.com/downloads/en/DeviceDoc/22049a.pdf>`_ ). One +of the regulators supplies power to the digital voltage plane; the +other supplies power to the analog voltage plane. + +These voltage regulators nominally take an input of up to 16V. In +addition, while the maximum continuous output current for the board is +250mA, if you are powering the board off higher voltages the amount +off current it can supply goes down, due to the regulators needing to +dissipate the extra power. So if you are powering the board off 12V, +the max current is about 40mA at room temperature. In general (again, +at room temperature) the max power dissipation (PD) for the chip is +about .37W, and output current = PD/(Vin-Vout). For exact max current +calculations, please refer to the datasheet linked above. + +If you are planning to draw a lot of current from the Maple board, it +is necessary to provide input power as close to 3.3V as +possible. Powering the microcontroller circuitry and LEDs on the board +alone takes approximately 30mA, so if you are powering the board with +12V that leaves only 10mA (at best) available for powering any user +circuitry. Attempting to draw more than 10mA runs the risk of shorting +out the power regulators and bricking your board. .. _maple-mini-gpios: @@ -339,14 +370,12 @@ This section lists known issues and warnings for the Maple Mini Rev 2 .. _maple-mini-vin: * **Silkscreen Vin voltage mistake**: The silkscreen on the Maple Mini - falsely indicates that Vin may be supplied with up to 16 V. We - recommend an input voltage **no greater than 12 V**. - - The voltage regulator on the Mini is rated up to 16 V. However, our - tests indicate that as its input voltage approaches 16 V, its output - begins to rise to levels higher than those recommended by ST for - supplying the STM32F103CB. The limit of 12 V keeps the voltage - supplied to the processor at safe levels. + falsely indicates that Vin may be supplied with up to 16V. We + recommend an input voltage **no greater than 12V**, and potentially + even lower depending upon the current draw requirements of the + application. Please see :ref:`Power Regulation on the Maple Mini + <maple-mini-power-regulation>` for more information. + Recommended Reading ------------------- |