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TM4C123GH6PM: Battery power of Tiva C launchpad - is 5.6V input too much?

Michael Lowell
Prodigy 150 points
Part Number: TM4C123GH6PM


Hello, I wish to make my Tiva C Launchpad battery powered, I have 4 NIMH AA batteries which output 1.4V each when fully charged - in series this produces 5.6V. This will discharge to 1.2V during use.

My understanding the Vreg on the Tiva C says it can input a max of 5.5V - I am wondering if I substantially risk damaging the board by attaching 5.6V?

Direct connection would greatly simplify everything as I would not need a separate voltage regulator or an additional battery.

Something which also worries me is that motors will be used, I assume a large capacitor will be sufficient to absorb voltage spikes is this sufficient?

 

  • 0
    Guru 117855 points

    Should 5V6 exceed the "absolute maximum ratings" of that VReg - even though the excess is slight - it is (still) outside of "best practice" to operate under those conditions.    Operating too close to - yet w/in "Abs Max" is also, "Not recommended."

    Two solutions bubble up:

    • insert a Schottky Diode - of proper current rating - in series with the "battery-pack's" (+) lead and the board's 5V input.   (this will "cost" you 0V3 (on average) but safeguard the VReg.
    • Replace the "on-board, restricted input VReg, w/one more accepting of (your) input voltage conditions.

    That (diode) suggestion provides a second (critical) benefit - it guards against, "Reverse Battery Connection and Reverse Battery Insertion (w/in a holder)" - either "sure" to wreak major damage to your board.

    You may also consider Li-Ion batteries - spec'ed to output 4V2 when fully charged - and descending to 3V6 (recharge point) - feeding into your (existing) LDO VReg.   (although you'll LOSE the protection of the series diode in so doing.)   "Proper" paralleling of several such Li-Ion batteries will "spectacularly" extend the "Operating Time" of your LPad...   (this vendor/others - produce chips which insure "proper paralleling" (i.e. load share) of Li-Ion batteries.)

    Note too that (even) placing (several) Li-Ion batteries in parallel - will (still) yield a "weight reduction" when contrasted against 4 NiMH batteries.    And - those 4 "series connected" "NiMH" batteries ADD the impedance of each/every cell to your board.    My suggestion of 2-3 Li-Ion units - properly paralleled - reduces the battery impedance by 50 or 67% - leaving "that much more energy" and/or operating time - available for your use!   And - that "Reduced Battery Impedance" makes them "more effective" in absorbing damaging voltage spikes - another key/critical advantage...