<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">To all, <div><br></div><div>Wow, great and thoughtful responses - it seems that I did both under and over think this. </div><div><br></div><div>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:</div><div><br></div><div>- 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</div><div>- 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!</div><div>- 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 <a href="http://cds.linear.com/docs/en/datasheet/29156fa.pdf">one</a> or is there a better way? Would be great if this logic was built into the DC-DC converter itself. </div><div>- 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.</div><div><br></div><div>Thank you all for your advice - I only hope I can learn enough to be able to return the favor someday.</div><div><br></div><div>Chip</div><div><br></div><div><br><div><div>On Jun 24, 2014, at 10:27 PM, <a href="mailto:triembed-request@triembed.org">triembed-request@triembed.org</a> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Send TriEmbed mailing list submissions to<br><span class="Apple-tab-span" style="white-space:pre"> </span><a href="mailto:triembed@triembed.org">triembed@triembed.org</a><br><br>To subscribe or unsubscribe via the World Wide Web, visit<br><span class="Apple-tab-span" style="white-space:pre"> </span>http://mail.triembed.org/mailman/listinfo/triembed_triembed.org<br>or, via email, send a message with subject or body 'help' to<br><span class="Apple-tab-span" style="white-space:pre"> </span>triembed-request@triembed.org<br><br>You can reach the person managing the list at<br><span class="Apple-tab-span" style="white-space:pre"> </span>triembed-owner@triembed.org<br><br>When replying, please edit your Subject line so it is more specific<br>than "Re: Contents of TriEmbed digest..."<br><br><br>Today's Topics:<br><br> 1. Power Supply Testing - Am I over or under thinking this?<br> (Martin Brooke)<br> 2. efficiency of power supply + thingy (Jim Sugaroo)<br> 3. Fwd: Re: Power Supply Testing - Am I over or under thinking<br> this? (Pete Soper)<br><br><br>----------------------------------------------------------------------<br><br>Message: 1<br>Date: Tue, 24 Jun 2014 13:46:10 -0400<br>From: Martin Brooke <martin.brooke@duke.edu><br>To: TriEmbed Discussion <triembed@triembed.org><br>Subject: [TriEmbed] Power Supply Testing - Am I over or under thinking<br><span class="Apple-tab-span" style="white-space:pre"> </span>this?<br>Message-ID:<br><span class="Apple-tab-span" style="white-space:pre"> </span><CALjzumpruzL9SjmUYAecwdOduEveJjaN5svY7WKC2NeKY0Bt7Q@mail.gmail.com><br>Content-Type: text/plain; charset="utf-8"<br><br>?The data sheet Figure 12 says that at 100mA load current you will be<br>around 90% +-5% efficient? for Battery 5.5V to 2.6 V after 2.6V you are on<br>your own! For 250mA the efficiency will be a bit worse particularly at<br>the lower voltages.<br><br>The voltage will stay at 3.3 V very precisely over that range but will have<br>a small ripple that will not change.<br><br>I think it will do what you want if used correctly.<br>-------------- next part --------------<br>An HTML attachment was scrubbed...<br>URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20140624/a10d1389/attachment-0001.html><br><br>------------------------------<br><br>Message: 2<br>Date: Tue, 24 Jun 2014 21:41:49 -0400<br>From: Jim Sugaroo <jim.sugaroo@gmail.com><br>To: triembed@triembed.org<br>Subject: [TriEmbed] efficiency of power supply + thingy<br>Message-ID:<br><span class="Apple-tab-span" style="white-space:pre"> </span><CAC2CVGzC-6pvaZr9isZR=dm=a+kD0nWkoTLSW94qpf4RHWoyMA@mail.gmail.com><br>Content-Type: text/plain; charset="utf-8"<br><br>Chip!<br><br>I'm used to seeing power supply efficiency as a function of load and mainly<br>when load is unknown such as a generic power supply. I don't think you<br>really need such a measurement over various load currents for your thingy.<br> I think your thingy has a specific load profile and you want to use it for<br>your test. I'm thinking you want to tweak your circuits, evaluate other<br>power supplies, change software, etc to get more *relative *battery life.<br><br>Here's my suggestion to evaluate changes and how efficient your power<br>supply + thingy operate:<br>1. Use the actual load of the micro and circuitry but have it wake up more<br>often and take a measurement, or not go to sleep, making constant<br>measurements. The goal here is to increase load for shorter test times but<br>keep same load profile. Depending on #4, you may not need to change<br>anything.<br>2. Have the thingy output a count value that is the count since power ON<br>and record this count value.<br>3. I'm assuming your have an under voltage lockout or some hysteresis in<br>your power supply such that it doesn't stutter as input voltage gets too<br>low.<br>4. Use a BFC as a power source, charge it up, with to Vin with SPST switch<br>(and resistor), then discharge it into your power supply that feeds the<br>thingy. Try a 10,000uF or do some time math to target a desired run time.<br>5. Measure the count value until it stops counting - when the voltage in<br>BFC is too low. Run it 5X and make sure its consistent - take an average<br>of the run times for a specific configuration.<br><br>You can use this count value to evaluate how efficient changes in your<br>design are. This will be a faster test than your actual application. Then<br>you can do long term testing using a real battery and real application but<br>it should correlate to this fast efficiency test. You could also calculate<br>energy/run-time which is an efficiency metric. The voltage decay of the<br>battery will not be the same as for a capacitor but I don't think that<br>matters much for your test.<br><br><br> Jim Sugaroo<br> -------------------<br> ---------------<br> -----------<br> --- ---<br> -- --<br> -- --<br> - -<br><br><br>On Tue, Jun 24, 2014 at 1:00 PM, <triembed-request@triembed.org> wrote:<br><br><blockquote type="cite">Send TriEmbed mailing list submissions to<br> triembed@triembed.org<br><br>To subscribe or unsubscribe via the World Wide Web, visit<br> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org<br>or, via email, send a message with subject or body 'help' to<br> triembed-request@triembed.org<br><br>You can reach the person managing the list at<br> triembed-owner@triembed.org<br><br>When replying, please edit your Subject line so it is more specific<br>than "Re: Contents of TriEmbed digest..."<br><br><br>Today's Topics:<br><br> 1. Power Supply Testing - Am I over or under thinking this?<br> (Charles McClelland)<br><br><br>----------------------------------------------------------------------<br><br>Message: 1<br>Date: Tue, 24 Jun 2014 11:29:13 -0400<br>From: Charles McClelland <chip@mcclellands.org><br>To: TriEmbed Discussion <triembed@triembed.org><br>Subject: [TriEmbed] Power Supply Testing - Am I over or under thinking<br> this?<br>Message-ID: <D55875FF-1168-4B93-8026-22727767AC2E@mcclellands.org><br>Content-Type: text/plain; charset="windows-1252"<br><br>To all,<br><br>In my never ending pursuit of longer battery life and / or less batteries,<br>I have been exploring moving from a linear DC-DC converter to a switching<br>power converter.<br><br>TI was gracious enough to send me some samples of their TPS63031<br>Buck-Boost Switching Power Supply which requires few external components<br>and with their WEBench and Switcher Pro tools, Pete and I were able to<br>create a simple board to test this chip. Pete lent his expertise and<br>lessons learned in working with these tiny QFN packages and we were able to<br>build one of these boards over the weekend.<br><br>Now I need to test it. I wanted to share my approach with this group to<br>make sure I am headed down the right track.<br><br>Major components:<br> - The TPS63031 which should maintain a constant 3.3V output as the<br>batteries drain from 5.5V to 1.8V<br> - A data logger<br> - Arduino (5V)<br> - Battery packs of various types up to 5.5V<br> - Some sort of load (like a 13.2 ohm 1W resistor)<br> - A ?high-side? current sensor like this one from Adafruit which<br>has an i2C output<br> - A Real Time Clock like the DS1307<br><br>Here is the under / over thinking part. In the end, I want to have a<br>rough idea how efficient this device is and whether is can maintain a<br>constant 3.3V voltage and 250mA current while the batteries run down.<br><br>My proposed approach is:<br> - Three power rails (Vin for the Power Supply, Vout for the Power<br>Supply and 5V for the Arduino) and a common ground<br> - A ?load? resistor connecting the Vout to ground<br> - A current / voltage sensor to measure on Vin<br> - I would then ask the Arduino to log the following every 30<br>seconds or so - Vin, Iin and Vout<br> - As long as the supply is delivering the 3.3V output, calculating<br>Iout would be the voltage divided by the fixed load reisitance<br><br>After the batteries die (Vout drops below 3.3V), I could calculate the<br>efficiency as the following:<br><br> - Instantaneous Efficiency % = (Vout * Iout) / (Vin * Iin) *100<br> - I think I could simply integrate the instantaneous efficiency<br>over the duration of the test to get the overall efficiency.<br><br>Am I thinking of this correctly?<br><br>Thanks, Chip<br><br>-------------- next part --------------<br>An HTML attachment was scrubbed...<br>URL: <<br>http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20140624/379e9912/attachment-0001.html<br><blockquote type="cite"><br></blockquote><br>------------------------------<br><br>Subject: Digest Footer<br><br>_______________________________________________<br>TriEmbed mailing list<br>TriEmbed@triembed.org<br>http://mail.triembed.org/mailman/listinfo/triembed_triembed.org<br><br><br>------------------------------<br><br>End of TriEmbed Digest, Vol 13, Issue 17<br>****************************************<br><br></blockquote>-------------- next part --------------<br>An HTML attachment was scrubbed...<br>URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20140624/e8602082/attachment-0001.html><br><br>------------------------------<br><br>Message: 3<br>Date: Tue, 24 Jun 2014 22:27:56 -0400<br>From: Pete Soper <pete@soper.us><br>To: Triangle Embedded Computing Discussion <TriEmbed@triembed.org><br>Subject: [TriEmbed] Fwd: Re: Power Supply Testing - Am I over or under<br><span class="Apple-tab-span" style="white-space:pre"> </span>thinking this?<br>Message-ID: <53AA33AC.10707@soper.us><br>Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"<br><br>(oops, used the wrong "reply" and this just went to Martin the first time.<br><br><br>-------- Original Message --------<br>Subject: <span class="Apple-tab-span" style="white-space:pre"> </span>Re: [TriEmbed] Power Supply Testing - Am I over or under <br>thinking this?<br>Date: <span class="Apple-tab-span" style="white-space:pre"> </span>Tue, 24 Jun 2014 22:26:13 -0400<br>From: <span class="Apple-tab-span" style="white-space:pre"> </span>Pete Soper <pete@soper.us><br>To: <span class="Apple-tab-span" style="white-space:pre"> </span>Martin Brooke <martin.brooke@duke.edu><br><br><br><br>The tests I'll be doing with one of these is measuring the temperature <br>rise for a given current output using an IR thermometer. We think the <br>thermal pad soldered pretty well, and Chip designed in a via connection <br>of the pad to a relatively large ground plane on the bottom side. Per <br>datasheet figure 5 <br><http://datasheet.octopart.com/TPS63031DSKT-Texas-Instruments-datasheet-10283974.pdf> <br>it appears the challenge will come with low input voltage (i.e. like <br>with an almost flat lithium cell) and high current output. I don't <br>expect to see .8A output sustained in this case (I expect the thermal <br>protection to cut in quickly). That is, I'll be surprised if the setup <br>can get by without a great deal of airflow and/or extra heat sink area <br>to reach its current limit in boost mode while still a mile away from <br>the spec lower limit for input voltage.<br><br>-Pete<br><br>On 06/24/2014 01:46 PM, Martin Brooke wrote:<br><blockquote type="cite">The data sheet Figure 12 says that at 100mA load current you will be <br>around 90% +-5% efficient for Battery 5.5V to 2.6 V after 2.6V you <br>are on your own! For 250mA the efficiency will be a bit worse <br>particularly at the lower voltages.<br><br>The voltage will stay at 3.3 V very precisely over that range but will <br>have a small ripple that will not change.<br><br>I think it will do what you want if used correctly.<br><br><br><br><br><br>_______________________________________________<br>Triangle, NC Embedded Computing mailing list<br>TriEmbed@triembed.org<br>http://mail.triembed.org/mailman/listinfo/triembed_triembed.org<br>TriEmbed web site:http://TriEmbed.org<br></blockquote><br><br><br>-------------- next part --------------<br>An HTML attachment was scrubbed...<br>URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20140624/ee21f8bf/attachment.html><br><br>------------------------------<br><br>Subject: Digest Footer<br><br>_______________________________________________<br>TriEmbed mailing list<br>TriEmbed@triembed.org<br>http://mail.triembed.org/mailman/listinfo/triembed_triembed.org<br><br><br>------------------------------<br><br>End of TriEmbed Digest, Vol 13, Issue 18<br>****************************************<br></blockquote></div><br></div></body></html>