SMT MintyBoost design

[PredatorCoder]

So I decided to learn gEDA and what better project to make than an SMT MintyBoost? So, here we are, with some improvements...

* Target enclosure is the same Altoids tin used by the ybox2 project. http://www.ladyada.net/images/ybox2/ybox_t.jpg. It is larger and can therefore use more batteries and larger inductors/capacitors.
* 3 AA battery holder will fit inside the target enclosure. If a larger enclosure is used, 6 AA batteries could be used (two 3 AA holders in parallel).
* TPS61032 boost regulator. It is rated for significantly higher switch current than MAX756. An example: MAX756 can provide 0.5A current at 3.6V input, whereas TPS61032 can do in excess of 2A. This should provide adequate current for more demanding USB devices, provided the batteries are up to the task.
* Undervoltage cutoff: if the batteries discharge too low, the load will be disconnected. This is to save the life of rechargable batteries, which can be destroyed by over-discharge.
* Reverse polarity protection: circuit will not fry if batteries are placed backwards.
* USB Battery Charging Specification 1.0 compatible. http://www.usb.org/developers/devclass_docs/batt_charging_1_0.zip. This is achieved by shorting D+/D- pins, as per the spec. (Can be disabled via DIP switch). Additionally if the batteries are adequate, the 1.5A current should be available.
* Various other pull-ups/pull-downs can be added to achieve further device compatibility that are not USB battery spec compliant. These can be enabled/disabled via DIP switches. I'm not sure what the best values to use here are to achieve best compatibility, so any feedback here would be welcome! It all seems like black magic to me, since nobody seems to know how the official chargers are wired and I don't personally have any USB chargable devices yet beyond a Bluetooth headset (which does not use D+/D- pins at all).

What's missing? Low battery LED. Because the comparator of the switcher is used for under-voltage cutoff, it is not usable for low battery LED. Therefore a separate analog comparator would be needed. I decided to just save costs and leave this out. Since this is used for charging batteries and not driving a critical load, I don't think this is an important feature to maintain.

This design is untested, sometime I might get around to making it, working out the kinks, and testing its real-world current-delivering capabilities with NiMH batteries.

I'm curious how many people are interested in this. If enough, I might be up for doing a batch order from gold phoenix and/or produce a few completed designs. Parts can be sourced 100% from Mouser.

Attached is the schematic and renders of gerber files.

Grr.... can't attach anything... let alone PDFs (which look the best). PNG on Flickr will have to do...

http://farm4.static.flickr.com/3132/2586780087_3bb8d9938a_o.png
http://farm4.static.flickr.com/3277/2586780145_ef03a214e8_o.png

[Bowman]

hi.

Sorry bad English ... but here we go

i have worked on a lt1302 based step up for some months now...

i used allot time on forums to try too find a good solution before i thought that it had too bee possible too see how the original apple usb recharger's was build... so i buyed one an cut it apart.. here are some photos..:

Recharger from top
http://hakon.boman.googlepages.com/appleusbtop.jpg
Recharger PCB (Bottom)
http://hakon.boman.googlepages.com/usbpcb.jpg


and a schematic


Here are a nice web site about smd resistors and values...
http://www.talkingelectronics.com/ChipDataEbook-1d/html/SM-Resistors.html

Here are a small proto-type i made..


And a image showing that it is working... ( NOT WORKING WITH MINTY BOOST as it cant deliver enough mA)
http://hakon.boman.googlepages.com/_MG_3466.jpg

back to my lt1302 i have a huge problem...
wen running off 2x AA the battery Voltage drops way below 2V probably because of the amps being driven form them...

the same problem when running off 3x 1,2V rechargeable ..

here are the data-sheet of the batteries...
GP "super Alkaline" AA 1,5V
http://www.gpbatteries.com/pic/GP15A_DS.pdf
GP "2700 Series" AA NIMH 1,2V
http://www.gpbatteries.com/pic/270AFH.pdf

more info will come but i have to go from school for today (i don't have that much equipment at home) I will not be back at school before Monday.. but i´m going too work a bit at home with it...


And YES I really want a working recharger (even if i cant use what i have used this much time on

[PredatorCoder]

I briefly looked at LT1302 datasheet, it looks like the TPS61032 can handle higher switch currents (although not a great deal more). But I would think LT1302 could still do the job if built/designed properly. Have you carefully tested your LT1302 design? Run it off a bench 2.7V supply like you're doing, check the open-circuit voltage, then start loading it and figure out what load is needed before the output voltage drops out of spec (below 5V). Then you can figure out what the maximum load really is for that part. If you get 2V when it's open-circuit or with a minimal load, then something is probably severely wrong with your design.

Another thing that would be useful to check: how many amperes does the iPhone use when charging from your little prototype adapter? This would be extremely useful information... Unfortunately the one in your photograph seemed to be broken, I was reading 0 amperes current? The time to measure this value would be when the battery is ~50% charging (the current will taper off when the lithium ion battery fills) and probably while simultaniously making a phone call or something.

Figure 9 in the TPS61032 datasheet seems to clearly indicate that the TPS61032 should cough up over 1 A current before it starts to drop out of regulation. Again I haven't scrutinized the LT1302 datasheet but if the switch current ratings aren't much less I would think it could do it, too. We'll know more once you characterize your design as previously described.

Therefore the remaining question becomes, can the batteries cough up the needed current? NiMH chemistry is best for this, and the datasheet you linked shows that the chemistry is more than capable of this task.

Thanks for ripping apart that USB charger! I'm sure a lot of people on the forum will find that to be very useful information besides myself.

[Bowman]

1. When there are no load on the lt1302 the voltage is the same as wen its not connected at all... (since id goes to standby)

I have worked on getting as low ripple as possible... (using the power supply)
when under load (ca500mA, 10Ohm) and started today to test it with batteries... (and was shocked to see the result)

http://hakon.boman.googlepages.com/_MG_3477.JPG
Battery Voltage: 3.39V
Volt out: 4.86V
Battery drain: 851mA

2 min after:
http://hakon.boman.googlepages.com/_MG_3491.JPG
Battery Voltage: 2.41V
Volt out: 4.38V
Battery drain: 1640mA

image of the pcb:
http://hakon.boman.googlepages.com/_MG_3504.JPG
the green part under lt1302 is a so8-> Dil 8 adapter.. makes it easier to move the IC from one prototype too another..


The iphone/ ipod Touch (using ipod today) uses 500-100mA (it recharges with 1000mA (and states so in Hw info, an app that shows HW info ) when given that much... but it can recharge properly from 500mA too... (haven't tested with less)

2: the amp and Volt meters on the power supply only works for the variable output... not the fixed 5 /12V


Updated last post with image of open recharger from top..
I think i will make a new one on Monday (if i have enough parts...)

[PredatorCoder]

For ripple, I would look into at least one low ESR tantalum capacitor for the output (solid-state aluminum electrolytic caps can be useful here too). According to the LT1302 datasheet, 0.06 ohm ESR or higher will cause it to make a mess (5V output). Look at page 8 for maximum allowed ESR calculations. Further reducing ESR will decrease ripple. (I have no idea what the ESR is of your existing output capacitor, you should look this up if you haven't already).

If output ripple is still unacceptable after doing the previous, an LC filter on the output can be used. This seems to describe it well.... http://www.ericsson.com/campaign/powermodules/archive/picov/28701-EN_LZT14606_EN_A_PDFV1R2.pdf

Hooking up the output of your regular to an oscilloscope would be a most useful thing to do if you really want to put some numbers on what these parameters might be in your actual circuit.

You could also try simulating the switcher in SPICE - Linear provides a free environment to do that in with their parts (SwCad). See if theoretical != reality. And see how altering circuit components would affect various characteristics of the switcher. If nothing else it would be a good excuse to learn SPICE.

I'm not sure why you have no output voltage when there is no load. That makes no sense to me. You should have an open-circuit voltage of 5V. Something's wrong if that's not the case. (or else the shutdown pin is enabled).

I take it you tested with non-rechargeable alkalines? Your 2 minute figure is not surprising if so. I experienced similar runtimes in another application. Try NiMH, you will likely have much better results. Alternatively, you'll just have to put (many) more batteries in parallel. Alkalines are designed for small loads over long periods of time.

[Bowman]

the output capacitor are a 100uF sanyo os-con cap, "16SA100M"
Data sheet:
https://www1.elfa.se/data1/wwwroot/webroot/Z_DATA/b3364d60-792a-11dc-bb36-0019bbdf5d02.pdf

I have only a few old scope photos... (of this circuit) I will take some new one on Monday i think...

I'm not sure why you have no output voltage when there is no load. That makes no sense to me. You should have an open-circuit voltage of 5V. Somethings wrong if that's not the case. (or else the shutdown pin is enabled).

sry i must have been unclear.. (not very good in wrighten English )

when there are no load the in voltage is the same as when the circuit is not connected too the barrettes (no Voltage drop)

the out voltage is then ca 5V

the shutdown pin is the metal conductor in top of the PCB... (always connected to GND)


the Battery Voltage drops fast with nimh batteries... (the 2700mAh gp)

I will do some testing on Monday with fresh batteries and maybe alternative PCB layout..

[Bowman]

sorry that i haven't posted updates last week...
during this week i have done some testing...

Monday i tested the circuit with 3 NiMH batteries...it run perfectly for 1.5 hours, and then I had to take everything down and go home.. after 3-4hours i put it back together, and it run for about 30 min more... ( a total of about 2 hours) this with the 10ohm resistors as a load.. (ca 500mA)

i havent got time to run a complete test... but on Wednesday i run a test with my ipod touch, using 3x 1.2V Nimh batteries it managed a full recharge and still had some power left in the batteries..


Edit:
I have now tested it to recharge my ipod touch with FW 2.0 using 3x 1,5V "Energizer Ultimate Lithium" batteries

ipod fully recharged after 2hour and 30 min..

after 5-6hours of heavy usage the ipod is empty again...

after 1hour and 10 min the current from the batteries jumped too 1.6A (from 6-900mA) and the circuit started to make a high pitched sound. so I removed the batteries.
iPod was then 70-80% recharged


a full test with nimh will come, probably tomorrow (Monday 7.7.08 )

I will post more info and photos/ videos tomorrow when i´m at school.
(much faster too upload with a 300mbit line than my 300kbit )

I will also try too get time too ech one new pcb...

[adafruit]

the next v of the mintyboost will be lt1302 based. while having electrolytics on the output does mean there's some ripple, it works OK (all apple products undoubtedly have some regulation on the input USB to account for the variety of USB power control chipsets). anyhow it works fine altho i couldnt get 600 mA out of it. 400-450 seemed about max before it drooped. still, thats 2x improvement from a max756

[Bowman]

Do you know when the next version will be available?

[adafruit]

a few weeks maybe a few months

[woody1189]

whats the current draw from the batteries when outputting 5v at 400~450ma?

[adafruit]

whats the current draw from the batteries when outputting 5v at 400~450ma?

http://www.ladyada.net/make/mintyboost/process.html

[woody1189]

i've seen that before; it shows what the draw for 100 and 250ma loads are but im wondering if you've tested the lt1302 yet and have measured the current draw from the batteries when outputting 450ma. im trying to wire a solar panel to the thing instead of two aa cells so im trying to gauge how much current i need to be able to output at 3v.