[TriEmbed] TriEmbed Digest, Vol 13, Issue 18
Charles McClelland
chip at mcclellands.org
Wed Jun 25 09:51:34 CDT 2014
To all,
Wow, great and thoughtful responses - it seems that I did both under and over think this.
Since Pete is handling the load and thermal testing, I should probably look at this this power supply functions with the actual circuit I am testing in addition to the fixed load run-down test. Here are the things I heard and a couple questions on how to do them:
- Jim C pointed out that I need to ensure that the low current load when the Arduino is asleep will be sufficient for the supply to maintain 3.3V - good thing to test
- Jim S - I really like the super cap idea - had never thought of that but it will greatly reduce the testing time and since I know the capacity of the capacitor - no high-side power measurement needed!
- Jim S - Had not thought about the under voltage lock out - big miss. According to the data sheet, there is an under voltage lockout on Vin but not Vout and the stutter issue could be a problem. Is there a solution you would recommend to this problem? The power supply has an “enable” pin which I could use in the next rev of the board but how would I tell the circuit to bring that pin low when Vout goes below 3.3V and keep it low if the circuit stutters? Do I need to add a voltage supervisor chip like this one or is there a better way? Would be great if this logic was built into the DC-DC converter itself.
- Martin - great point on the current - I need to reduce the current load if I want to test the batteries running all the way down in the battery testing phase.
Thank you all for your advice - I only hope I can learn enough to be able to return the favor someday.
Chip
On Jun 24, 2014, at 10:27 PM, triembed-request at triembed.org wrote:
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> Today's Topics:
>
> 1. Power Supply Testing - Am I over or under thinking this?
> (Martin Brooke)
> 2. efficiency of power supply + thingy (Jim Sugaroo)
> 3. Fwd: Re: Power Supply Testing - Am I over or under thinking
> this? (Pete Soper)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 24 Jun 2014 13:46:10 -0400
> From: Martin Brooke <martin.brooke at duke.edu>
> To: TriEmbed Discussion <triembed at triembed.org>
> Subject: [TriEmbed] Power Supply Testing - Am I over or under thinking
> this?
> Message-ID:
> <CALjzumpruzL9SjmUYAecwdOduEveJjaN5svY7WKC2NeKY0Bt7Q at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> ?The data sheet Figure 12 says that at 100mA load current you will be
> around 90% +-5% efficient? for Battery 5.5V to 2.6 V after 2.6V you are on
> your own! For 250mA the efficiency will be a bit worse particularly at
> the lower voltages.
>
> The voltage will stay at 3.3 V very precisely over that range but will have
> a small ripple that will not change.
>
> I think it will do what you want if used correctly.
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> Message: 2
> Date: Tue, 24 Jun 2014 21:41:49 -0400
> From: Jim Sugaroo <jim.sugaroo at gmail.com>
> To: triembed at triembed.org
> Subject: [TriEmbed] efficiency of power supply + thingy
> Message-ID:
> <CAC2CVGzC-6pvaZr9isZR=dm=a+kD0nWkoTLSW94qpf4RHWoyMA at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Chip!
>
> I'm used to seeing power supply efficiency as a function of load and mainly
> when load is unknown such as a generic power supply. I don't think you
> really need such a measurement over various load currents for your thingy.
> I think your thingy has a specific load profile and you want to use it for
> your test. I'm thinking you want to tweak your circuits, evaluate other
> power supplies, change software, etc to get more *relative *battery life.
>
> Here's my suggestion to evaluate changes and how efficient your power
> supply + thingy operate:
> 1. Use the actual load of the micro and circuitry but have it wake up more
> often and take a measurement, or not go to sleep, making constant
> measurements. The goal here is to increase load for shorter test times but
> keep same load profile. Depending on #4, you may not need to change
> anything.
> 2. Have the thingy output a count value that is the count since power ON
> and record this count value.
> 3. I'm assuming your have an under voltage lockout or some hysteresis in
> your power supply such that it doesn't stutter as input voltage gets too
> low.
> 4. Use a BFC as a power source, charge it up, with to Vin with SPST switch
> (and resistor), then discharge it into your power supply that feeds the
> thingy. Try a 10,000uF or do some time math to target a desired run time.
> 5. Measure the count value until it stops counting - when the voltage in
> BFC is too low. Run it 5X and make sure its consistent - take an average
> of the run times for a specific configuration.
>
> You can use this count value to evaluate how efficient changes in your
> design are. This will be a faster test than your actual application. Then
> you can do long term testing using a real battery and real application but
> it should correlate to this fast efficiency test. You could also calculate
> energy/run-time which is an efficiency metric. The voltage decay of the
> battery will not be the same as for a capacitor but I don't think that
> matters much for your test.
>
>
> Jim Sugaroo
> -------------------
> ---------------
> -----------
> --- ---
> -- --
> -- --
> - -
>
>
> On Tue, Jun 24, 2014 at 1:00 PM, <triembed-request at triembed.org> wrote:
>
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>> Today's Topics:
>>
>> 1. Power Supply Testing - Am I over or under thinking this?
>> (Charles McClelland)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Tue, 24 Jun 2014 11:29:13 -0400
>> From: Charles McClelland <chip at mcclellands.org>
>> To: TriEmbed Discussion <triembed at triembed.org>
>> Subject: [TriEmbed] Power Supply Testing - Am I over or under thinking
>> this?
>> Message-ID: <D55875FF-1168-4B93-8026-22727767AC2E at mcclellands.org>
>> Content-Type: text/plain; charset="windows-1252"
>>
>> To all,
>>
>> In my never ending pursuit of longer battery life and / or less batteries,
>> I have been exploring moving from a linear DC-DC converter to a switching
>> power converter.
>>
>> TI was gracious enough to send me some samples of their TPS63031
>> Buck-Boost Switching Power Supply which requires few external components
>> and with their WEBench and Switcher Pro tools, Pete and I were able to
>> create a simple board to test this chip. Pete lent his expertise and
>> lessons learned in working with these tiny QFN packages and we were able to
>> build one of these boards over the weekend.
>>
>> Now I need to test it. I wanted to share my approach with this group to
>> make sure I am headed down the right track.
>>
>> Major components:
>> - The TPS63031 which should maintain a constant 3.3V output as the
>> batteries drain from 5.5V to 1.8V
>> - A data logger
>> - Arduino (5V)
>> - Battery packs of various types up to 5.5V
>> - Some sort of load (like a 13.2 ohm 1W resistor)
>> - A ?high-side? current sensor like this one from Adafruit which
>> has an i2C output
>> - A Real Time Clock like the DS1307
>>
>> Here is the under / over thinking part. In the end, I want to have a
>> rough idea how efficient this device is and whether is can maintain a
>> constant 3.3V voltage and 250mA current while the batteries run down.
>>
>> My proposed approach is:
>> - Three power rails (Vin for the Power Supply, Vout for the Power
>> Supply and 5V for the Arduino) and a common ground
>> - A ?load? resistor connecting the Vout to ground
>> - A current / voltage sensor to measure on Vin
>> - I would then ask the Arduino to log the following every 30
>> seconds or so - Vin, Iin and Vout
>> - As long as the supply is delivering the 3.3V output, calculating
>> Iout would be the voltage divided by the fixed load reisitance
>>
>> After the batteries die (Vout drops below 3.3V), I could calculate the
>> efficiency as the following:
>>
>> - Instantaneous Efficiency % = (Vout * Iout) / (Vin * Iin) *100
>> - I think I could simply integrate the instantaneous efficiency
>> over the duration of the test to get the overall efficiency.
>>
>> Am I thinking of this correctly?
>>
>> Thanks, Chip
>>
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> Message: 3
> Date: Tue, 24 Jun 2014 22:27:56 -0400
> From: Pete Soper <pete at soper.us>
> To: Triangle Embedded Computing Discussion <TriEmbed at triembed.org>
> Subject: [TriEmbed] Fwd: Re: Power Supply Testing - Am I over or under
> thinking this?
> Message-ID: <53AA33AC.10707 at soper.us>
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> (oops, used the wrong "reply" and this just went to Martin the first time.
>
>
> -------- Original Message --------
> Subject: Re: [TriEmbed] Power Supply Testing - Am I over or under
> thinking this?
> Date: Tue, 24 Jun 2014 22:26:13 -0400
> From: Pete Soper <pete at soper.us>
> To: Martin Brooke <martin.brooke at duke.edu>
>
>
>
> The tests I'll be doing with one of these is measuring the temperature
> rise for a given current output using an IR thermometer. We think the
> thermal pad soldered pretty well, and Chip designed in a via connection
> of the pad to a relatively large ground plane on the bottom side. Per
> datasheet figure 5
> <http://datasheet.octopart.com/TPS63031DSKT-Texas-Instruments-datasheet-10283974.pdf>
> it appears the challenge will come with low input voltage (i.e. like
> with an almost flat lithium cell) and high current output. I don't
> expect to see .8A output sustained in this case (I expect the thermal
> protection to cut in quickly). That is, I'll be surprised if the setup
> can get by without a great deal of airflow and/or extra heat sink area
> to reach its current limit in boost mode while still a mile away from
> the spec lower limit for input voltage.
>
> -Pete
>
> On 06/24/2014 01:46 PM, Martin Brooke wrote:
>> The data sheet Figure 12 says that at 100mA load current you will be
>> around 90% +-5% efficient for Battery 5.5V to 2.6 V after 2.6V you
>> are on your own! For 250mA the efficiency will be a bit worse
>> particularly at the lower voltages.
>>
>> The voltage will stay at 3.3 V very precisely over that range but will
>> have a small ripple that will not change.
>>
>> I think it will do what you want if used correctly.
>>
>>
>>
>>
>>
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