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Diffstat (limited to 'source/hardware/maple.rst')
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diff --git a/source/hardware/maple.rst b/source/hardware/maple.rst index 610fdfc..aff64d5 100644 --- a/source/hardware/maple.rst +++ b/source/hardware/maple.rst @@ -103,15 +103,50 @@ header. This pin feeds into both the digital and analog voltage regulators. However, don't do this while simultaneously powering the board from another source, or you could damage it. +When powering the board from a barrel jack, **double check the +polarity of the barrel.** The appropriate polarity is noted on the +silkscreen right next to the connector. + .. warning:: Silkscreens on Maples up through Rev 5s manufactured in Spring 2011 falsely indicated that the barrel jack could be - supplied by up to 18 V. We recommend a barrel jack input voltage - **no greater than 12 V**. - - Rev5s manufactured after Spring 2011 may still have this error on - the silk, but it has been marked over. - - See :ref:`this erratum <maple-barrel-jack>` for more information. + supplied by up to 18V. (Rev5s manufactured after Spring 2011 may + still have this error on the silk, but it has been marked over.) We + recommend a barrel jack input voltage **no greater than 12V**, and + potentially even lower depending upon the current draw requirements + of the application. The same goes for powering off LiPo batteries. + + Please see :ref:`Power Regulation on the Maple + <maple-power-regulation>` for more information. + +.. _maple-power-regulation: + +Power Regulation on the Maple +----------------------------- + +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. Using the Built-in Battery Charger ---------------------------------- @@ -423,15 +458,16 @@ General * **Barrel jack power supply voltage mistake**: The acceptable voltage range given next to the barrel jack on the Maple through Rev 5s - manufactured in Spring 2011 is **incorrect**. The given range is 7 - V — 18 V. In fact, **18 V is too high** and should not be supplied - to your board. The recommended maximum voltage you should apply is - **12 V**. - - The original voltage regulators used on the Maple were rated up to - 18 V. However, the voltage regulators on current Maple Revs are - rated up to 16 V. Our tests indicate that they operate correctly - through 12 V. We do not recommend higher input voltages. + manufactured in Spring 2011 is **incorrect**. The given range is 7V + — 18V. In fact, **18V is too high** and should not be supplied to + your board. The original voltage regulators used on the Maple were + rated up to 18V. However, the voltage regulators on current Maple + Revs are rated up to only 16V, and due to the current draw + requirements of the board, operate properly only up to 12V. The + recommended maximum voltage you should apply is **12V**, and + potentially even lower depending upon the current draw requirements + of the application. Please see :ref:`Power Regulation on the Maple + <maple-power-regulation>` for more information. .. _maple-nrst-pb4: |