Elaborate mobile CMoy Design - need a little help - diyAudio
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Old 28th April 2011, 08:40 AM   #1
NebuK is offline NebuK  Germany
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Default Elaborate mobile CMoy Design - need a little help

Heyyas, i'm just learning myself more into amplifier design, pcb layouting and everything else that has to do with it. So i'm currently trying to design a quite elaborate mobile cmoy amplifier for my headphones ...

I'm planning on using a single cell LiIon (or LiPoly) battery charged by a ADP2291 integrated LiIon charger. Then i want to boost the ~3.6-4.5V to some ~18V by using a TI tps61085t boost converter. As that converter doesn't seem good with high-frequent load-changing conditions i lowpassed the loadchange by using three 1000uF caps after it. Then i split the Vccs and producea virtual ground by using a simple opamp-voltage-follower (is that the correct name for it?) so i get +-18V symmetric supply which i put into the "standard" cmoy circuit - which i realized using AD8620 OpAmp.

The circuit and first try of a PCB-Layout can be found on Index of /cmoy . I'm designing in DipTrace (which is Freeware, sadly not Free Software ...) - For those interested enough to install it and have a look on my work - i'm keeping it in a GIT on amps - Gitorious . There i also collected all the datasheets i've found for the parts i'll be using (hopefully Oo).


Now ... there are a "few" things i'm heavily unsure about and that i'd like to ask for help here... I think i'll just be trying to list them all and hope for some expert here to be able to help me .

So first questions are about the charger circuit - which is "self terminating" the application note from the datasheet. There i have two questions - first the Resistor R1 which is valued with "200mOhm" in the datasheet ... that is milli, right? Somehow my preferred electronics distributor (reichelt.de, in Germany) doesn't seem to have 200milli-Ohms 1206 resistors - can that really be or am i beeing dumb or blind?!? The next question would be the Q2, the 2N7002 - will that one work there?

Okay, on to the most complex part, the boost step-up converter. There i'm unsure about pretty much everything - will that thingy like the heavy output buffering? I tried to iterate me through the values using TIs "SwitcherPro" power-stage designer - the total output gain in their simulated graph using the values shown had the 0db-hit at around 1kHz. My main question is about the choice of the cap values, inductor (i was plannung on using this fastron: L-PISM 3,3µ - SMD-Power-Induktivität, PISM, Ferrit, 3,3µ - Power-Induktivitäten, SMD bei Reichelt Elektronik - and the BAS40-04 ... will that at least more or less work?

I think the VGND and final opamp stage should be more or less okay... right?

Theeen the pcb layout - as i've pushed and pulled around quite some pads and made traces and ... well, this may be a diptrace specific question but - is there a nice way to check for false connections? And/Or whether all connections specified in the Schematic are still active and good? Well ... i think this ought to be enough of bugging you.

I'm looking forward to all kinds of suggestions and help~

Thanks in Advance and Kind Regards - NebuK

(PS: Sorry for the bad english, no native speaker here :P)

Last edited by NebuK; 28th April 2011 at 08:46 AM.
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Old 29th April 2011, 03:05 AM   #2
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Instead of creating your own virtual ground generator, how about using the TI TLE2426CLP to generate your virtual ground. It basically takes the Vrail and outputs a 1/2 Vrail to generate your Vground. This is used in the CMoyBB to generate the virtual ground from a single 9V battery. It is a standard TO-92 package, under $2 and super easy to implement (one pin is v-rail, one pin is ground, the last pin outputs your virtual ground).
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Old 29th April 2011, 08:31 AM   #3
NebuK is offline NebuK  Germany
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Hey,

thanks for the tip - i somehow overlooked that ICs for that purpose existed. Would be really convenient . Problem is - the electronics distributor where i want to order doesn't have them so ... if i ordered just two or three piece from mouser or similar i'd pay around 20Eur (~25$) for just three of those nifty little thingies ... that's a little too much for ;/.

Still, thanks alot! Will keep in mind for me next design :P.
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Old 29th April 2011, 06:35 PM   #4
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haha, yeah $25 would be ridiculous. Good luck with your design though. I am going to keep an eye on this thread to see how things turn out.
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Old 30th April 2011, 10:37 AM   #5
NebuK is offline NebuK  Germany
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Thanks But i really somehow hoped for some etec expert to - at least roughly - check the schematic. Before i order the parts i somehow wanted something like "could roughly work" - i'd be really really glad if someone could check my basic ideas again

Thanks in advance, kind regards
- NebuK
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Old 1st May 2011, 08:24 PM   #6
T in AZ is offline T in AZ  United States
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on your charger you have "do not get" R1 is the current sense resistor, 200m = .2 ohms
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Old 2nd May 2011, 12:30 AM   #7
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0R2 is 5 * 1R resistors in parallel.

Can't you show a screenshot of your design or make a .pdf at least (you can make them online @ adobe). It's a hassle installing a package just to look at what you've done. I have enough installed stuff cluttering up my computer, some of it hogging resources or slowing down boot. Or draw the schematic (or as close as you can) in LTSpice, which lots of people have. You can simulate in LTSpice, so it's not all wasted effort.

w
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Old 2nd May 2011, 10:30 AM   #8
NebuK is offline NebuK  Germany
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Heyyas, thanks for the replies . I've merged the schematics from Index of /cmoy into a pdf for convenience: http://pics.kanojo.de/cmoy/schematic.pdf - thanks for that note! About R1 - i somehow couldn't find a 0.2Ohms 1206 Resistor at my electronics distributor (reichelt.de) - are these very uncommon (newbie speaking here :P) or is it just me beeing very very blind? Also i don't really understand what you mean by "0R2 is 5 * 1R resistors in parallel." - R2 is for pulling !CHG to the right value, so the charger will charge, no? Anyways, thank you for helping me on my first design . Kind Regards - NebuK
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