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diff --git a/source/hardware/maple-native-beta.rst b/source/hardware/maple-native-beta.rst index f120c05..f1b2284 100644 --- a/source/hardware/maple-native-beta.rst +++ b/source/hardware/maple-native-beta.rst @@ -46,20 +46,57 @@ Technical Specifications Powering the Maple Native ------------------------- -The Maple Native may be powered from the barrel jack connector, USB, -or a LiPo battery. The power source is determined by the header -labeled "PWRSEL" on the silkscreen. Boards are shipped with a jumper -on the USB selector. In order to power it off of an alternative -source, unplug the Maple Native, then move the jumper to the desired -selector before reconnecting power. - -You can also power the Maple Native via the pin labeled "Vin" on the -vertical header to the right of the PWRSEL 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. - -We recommend an input voltage no greater than 12 V. +The power source is determined by the header labeled "PWRSEL" on the +silkscreen. The Maple Native may be powered from USB (marked "USB" on +the PWRSEL header), a LiPo battery (marked "BAT"), or one of the two +"Vin" pins (marked "EXT"). Boards are shipped with a jumper on the +USB selector. In order to power it off of an alternative source, +unplug the Maple Native, then move the jumper to the desired selector +before reconnecting power. + +The "Vin" line is available on the pin labeled "Vin" on the vertical +header to the right of the PWRSEL header, as well as on the +unpopulated two-pin connector on the upper left corner of the +board. On this latter connector, polarity was accidentally left +unmarked: the leftmost, round pin should be power, while the square +pin should be ground. + +When powering the Maple Native board from a battery or the Vin lines, +care must be taken not to over-voltage the board. In general, an upper +limit of 12V input is acceptable, but this may vary depending upon the +current draw requirements of the application. Please see :ref:`Power +Regulation on the Maple Native <maple-native-b-power-regulation>` for +more information. + +.. _maple-native-b-power-regulation: + +Power Regulation on the Maple Native +------------------------------------ + +Power regulation on the Maple Native 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 Native +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 ---------------------------------- |