Is it possible to connect a 5V battery directly to the Tiva C Series TM4C123G LaunchPad?

Hi cb,

Thanks for your explanation. Actually the idea of using a 7805 regulator is just because the L278N stepper motor driver board I have in my project has it already. However, as you can see in my reply above I connected directly the battery to the board VBUS rail and it worked perfectly. I tried to use that 7805 voltage regulator but as we could imagine there is not enough overvoltage to run it.

cb1_mobile said:

Finally - is your battery (really) 6V6?  Seems unusual - might you describe? 

The battery is from a salvaged device with special battery. I could save also the battery charger from that device so I can use it with my project right now.

However I'm about to have a new battery and a buck adjustable converter that is highly efficient.

cb1_mobile said:

And - there are commercial, rechargeable, encased battery packs which deliver 5V0 via a standard USB socket. (Many different sizes - we use these often to demo products/systems where AC power is not close/convenient...)

Could you please tell me some of those battery packs for 5V0 with standard USB socket?

Thanks for your help!

Kind regards,

Francisco

Hello cb,

Thanks for your explanations, and as you worried the disaster happened: Port E 0 and 1 digital inputs passed away. They don't work anymore but the board still works... I think it was not the voltage regulator what suffered more, but the digital inputs when higher voltage was plugged to them what went wrong.

After checking some other Ports inputs and general working, I have to say the board still works properly!

Now I'm feeding the board from USB waiting for the buck converter that will get down from 6.6V to 5V safely.

Lesson learned the hard way: don't go beyond specs. Thanks anyway for your warnings. Now I have also to order a new Tiva C board to have a full functional one...

Kind regards,

Francisco

Thanks Kel!

Kind regards,

Francisco

Francisco Dominguez1 said:

Port E 0 and 1 digital inputs passed away.

Our small group - dressed in black - dabbing at tears over departed PE0/1...  May they, "rest in (spec abuse) peace."

That said - sometimes you can get lucky - and reclaim pins proclaimed, "dead."  (Say what?)  Suggest that you switch those pins from input mode to output - and see if they "behave" under that utilization.  (different circuit paths exist - we've seen cases where the input, "is no more" - but the output path is reasonably intact.)   Note - I'd think twice (or more often) before placing that board upon spacecraft - or human implantation.  But - for Gov't work - may prove acceptable.  (i.e. trade 4 for 1!)

Those Power Packs earlier described are used often to recharge cell-phones.  However - any form of "custom usage" will raise the selling price significantly.  If you're still interested - look for the most generic version you can find.  Key I believe is USB socket for eased connection to "anything" and a built-in, separate connection which allows recharging.  These range in outputs from 500mA up to 10A, or so.  Note that the higher the power output - (usually) the longer it takes to recharge.  And one last "gotcha" - most USB ports can source just 500mA - packs I saw today sought up to 2A for fastest charging - and that likely means a, "real AC line, sourced" charger.

Do comply with specs - and try hard not to approach, "absolute maximums."

cb1_mobile said:

Finally - is your battery (really) 6V6?  Seems unusual - might you describe?

6V6 is what you would expect from a 3 cell standard PbS.  It's also reasonable for a 2 cell LiIon (3V3 *2)  Not likely for the nickel chemistries I'm familiar with though.

Robert

Robert Adsett said:

It's also reasonable for a 2 cell LiIon (3V3 *2)

We have a very recent shipment of 500 Li Ion - and cell maker and I very much dispute your 3V3 assertion!  Fully charged these approach 4V1-4V2 - but under regular service/use - 3V6 (which totals 7V2 for 2 such cells in series) is far more, normal/customary.  Any such cell decayed down to your 3V3 level is badly in need of recharge.  (or burial)

If you spend any time in review of Li Ion Power Tool (cordless) market - you'll immediately note: 7V2, 14V4 and 21V6 very much in dominance.  Each/every one of those voltages spring from 3V6 series string - and impossible to achieve from (newly proposed), 3V3.

Interesting that you seized on such a relatively minor point - when multiple points were in evidence.  (and most received poster's favorable comment/appreciation)

cb1- said:

Interesting that you seized on such a relatively minor point - when multiple points were in evidence.  (and most received poster's favorable comment/appreciation)

Merely an aside on the range of battery voltages available.  Not meant as either a solution or criticism of offered solutions.

As far as LiIon variants with a 3V3 nominal voltage, remember LiIon is an umbrella term covering a number of chemistries.  I was thinking of Lithium Iron Phosphate which does indeed have a 3V3 nominal voltage (Or sometimes called 3V2).  Terminal discharge can be as low as 2V7 but you are well over the discharge knee at that point except at high discharge rates.  I understand them to be popular with certain scale vehicle communities because they can withstand 5C or 10C discharges.  A good choice for cordless tools for the same high discharge capability.

I actually rather suspect those 3V6 cells in the cordless example are 3V3 cells labelled for their maximum charge voltage rather than their nominal voltage (and the voltage they actually sit at for most of the discharge life).  The inverse of voltage rating used on standard automotive PbS batteries.  Call it games marketers and battery manufacturers play.

Robert

cb1_mobile said:

Our small group - dressed in black - dabbing at tears over departed PE0/1...  May they, "rest in (spec abuse) peace."

Thanks to your small group -dressed in black - for those last regards to the pins that served at the highest technical levels.

I have tested both pins as inputs and outputs and I have to say they are completely dead :-( Maybe the analogue function on those pins are still there. I'll check it at some point in the future.

Even testing some other outputs in Port E I saw a lower level of green LED of power on when activating another output that still works...

With other ports the board works well, even driving some inputs and stepper motors, by a stepper drives of course.

I think having a power pack of 5V output is also good to use with my mobile phone ;-)

BTW, I'm testing this board with the 6V battery pack powering it with the 7805 output that actually it gives 4.13V and the Tiva C board still works (that is below the 4.75V specified at the Launchpad user's guide). You said about avoid absolute maximums, but what about minimums? I think it's only a question of just bad behaviour or just stop working due to low power voltage.

Hi Robert,

Sorry for the misinformation. The battery pack says 6V 4200mAh Ni-MH BATTERY. It has 5 cells, so I think it is Ok to have 1.2V per cell for being a Ni-MH.

Suggest that you positively provide "distance" between your operation and each/every Abs. Max.  Violation here is likely to prove injurious to the device.  (either immediately or via regular, increasing degradation...)

Compliance with all specs should be your goal.  Minimum violation may not cause so quick/severe a reaction - but if you "wander" from IC spec - you place yourself in, "No man's land."   Not the best place - and our group rarely attends 2nd funeral - and black garb is, "out for cleaning."  (Crockadillian tears however - remain in good supply)

cb1- said:

our group rarely attends 2nd funeral - and black garb is, "out for cleaning."  (Crockadillian tears however - remain in good supply)

We (my dear Tiva C board and myself) are sad that you couldn't attend a possible final funeral, thanks God we didn't expect to have it near future.

However a mixture of low fundings and maybe too far checking chances bring us to some point away from specs when testing. After last events I'm sure I'll follow strictly those specs. Thanks for your advice.

Francisco Dominguez1 said:

Sorry for the misinformation. The battery pack says 6V 4200mAh Ni-MH BATTERY. It has 5 cells, so I think it is Ok to have 1.2V per cell for being a Ni-MH.

Yes, 1V2 nominal voltage for NiMH.  The low voltage could be as low as 3V for heavy current draws but more likely 4 or 5V, the high as much as 7V.

You will find a lot of different chemistries with "6V" battery packs.  They cover quite a range of actual voltages but if you design your power inputs to accomodate the broad available range you get a lot of choice.

BTW you can get off the shelf buck switching supplies that are pin compatible with the 7805 family (down to 3V3 at least).

Robert

Francisco Dominguez1 said:

BTW, I'm testing this board with the 6V battery pack powering it with the 7805 output that actually it gives 4.13V and the Tiva C board still works (that is below the 4.75V specified at the Launchpad user's guide). You said about avoid absolute maximums, but what about minimums? I think it's only a question of just bad behaviour or just stop working due to low power voltage.

I agree with cb1's injunction here.  Avoid the Abs Max. ratings.  Most devices are not guaranteed to work at those ratings, only to survive.  Most ICs will have a recommended operating range, that is the range you should strive to stay within.

Specifically on the low voltage end, you could see

• the IC "stops"
• random behaviour
• drifting out of specification
• destruction (the IC inputs/outputs can end up in undefined states that dissipate a lot of power)

The last is usually rare, thankfully.

Robert