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Need some Help Topic: portable DAC power supply

post #1 of 19
Thread Starter 

Hi,

 

although I lurk around here for a long time and tried DIY some stuff, recently I discovered that I have a great knowledge deficit when it comes to electronics / schematics / PCB design, etc.... however I started to read educate myself in that direction. Sadly it is quite a lot information I gathered and difficult for me to handle. I realized that I have to start more or less from the bottom if I want to design stuff myself.

 

At the moment I am trying to design a power source schematic for my DAC chip (AD1955). That DAC needs 2 5v supplies (DVDD & AVDD) I know that there are some schematics already available using 9v batteries yet there are none with 3.7v batteries. However I want to do this with a Samsung Galaxy S battery (lots of them available for cheap). My question is: Can I use charge pump regulators to power the DAC?

 

I made a sketch (I am not so good yet in drawing schematics) of how I intend to solve this problem:

 

 

 

I know this is not much information I gave you, but there are lot of those regulator ICs available as option, I just do not know, if I am making a major mistake by doing this. I am reading stuff about this voltage-ripple that comes from ragulators => is this possibly relevant to SQ of a DAC?

 

Thank you very much for any input I get :D

post #2 of 19
Thread Starter 

Sadly nobody can answer my question, whether or not I can use a charge pump regulator as analog voltage supply. :( However I will try it out.

 

Instead of the AD1955 I will use the CS4398, because in the end I only need one of these regulators, just for the analog voltage supply. The digital voltage supply just needs 3.3v.

 

Here are some sketches, that look more like schematics:

 

This is more or less the schematic around the CS4389. What is missing? 3.3v voltage regulation, I2C connection, I2S connsection, the opamp. I will try to make a small board for testing, before going into something larger, therefore I2C and I2S will lead in connectors. Plan is to try things out first with one of my STM32 boards :)

 

Aaaand this is some schematic f the MAX682. That is the chargepump regulator in question for the analog supply.

 

This is the TPA6130A2 amp section.

 

Now I have to stick all this together with Eagle Cad or some similar program. The result, I hope, will be some kind of small dev board that I can try out with my STM32F4 discovery.

 

This is my first project and I am open to any suggestions, tips questions :D


Edited by RAFA - 10/5/12 at 8:22am
post #3 of 19

What are you trying to accomplish? A portable DAC implies there is a computer to send a stream of bytes over some interface to your DAC. Typically, that is done via USB.

 

But portable music players already have DACs and low voltage amplifiers for battery operation. I am not an engineer but I suspect you would have significant noise and/or distortion to deal with if everything runs from a single 3.7v battery.
 

post #4 of 19
Thread Starter 
Quote:
Originally Posted by fubar3 View Post

What are you trying to accomplish? A portable DAC implies there is a computer to send a stream of bytes over some interface to your DAC. Typically, that is done via USB.

 

But portable music players already have DACs and low voltage amplifiers for battery operation. I am not an engineer but I suspect you would have significant noise and/or distortion to deal with if everything runs from a single 3.7v battery.
 

 

The plan is to make a portable music player that you can stick on a SATA-hd. 1.8" are available up to 320gb and 2.5" "thin editions" are available up to 750gb or a SSD, actually it should not be important what HD you plug on...

 

For the beginning it will be just a small dev-board with I2S input and also I2C so I can test things out.

 

The noise and distortion could really be a problem, but so far the components that I am using do not really consume that much of power. How is it possible for the Sflo2 to be without distortion with low noise and having 2 DACs + opamp all powered by a 3.7v battery.

 

In the end I cannot say exactly that all this will work, but I will try :D


Edited by RAFA - 10/6/12 at 2:21am
post #5 of 19

Why not 2S LiFePO4 battery pack (down to +4VDC, high current capability and very fast 10C charging) and an LDO regulator? Switching needs filtering!

 

TI LMZ12001 for +4.5VDC<VIN<+20VDC and the RON functionality to preserve the batteries from deep discharge.

 

And do you think about the charging circuit? The BMS?
 

post #6 of 19
Thread Starter 
Quote:
Originally Posted by jpaul64 View Post

Why not 2S LiFePO4 battery pack (down to +4VDC, high current capability and very fast 10C charging) and an LDO regulator? Switching needs filtering!

 

TI LMZ12001 for +4.5VDC<VIN<+20VDC and the RON functionality to preserve the batteries from deep discharge.

 

And do you think about the charging circuit? The BMS?
 

 

Thank you for your suggestions, even though the battery in terms of power would be a dream, it is just too long and thick for my planned project. BUT, you made me come to an idea. I could use 2 SGS batteries in series.

 

Yes I need a battery management system and a protection circuit.

 

Thank you for you input, but I will need some days to grasp that stuff also I am struggling with Eagle Cad.


Edited by RAFA - 10/6/12 at 1:45pm
post #7 of 19

Charger Microchip MCP73223 for 2S LiFePO4. Overcharging protection included! With LMZ you become the UV protection. Le tour est joué! Ok, MCP is DFN package, manuel soldering impossible!
 

post #8 of 19

Eagle is a very simple tool! You need only a good biblio. COMe i7 Mainboard.


Edited by jpaul64 - 10/6/12 at 2:05pm
post #9 of 19
Thread Starter 
Quote:
Originally Posted by jpaul64 View Post

Eagle is a very simple tool! You need only a good biblio. COMe i7 Mainboard.

 

 

Is this your work? It is crazymazing :D

 

Do not worry about soldering DFN. I managed to solder BGA at home with a ceran cooking plate.

post #10 of 19

... and with two SSD not larger than a 5,25" drive. Active dissipation, IP65 enclosure (externally mounted fans), military project. the routing of USB 3.0, DVI, HDMI, LAN, PCIe was a little bit difficult with Eagle but successfull. You can do a lot of things with these tool, see Eagle 3D...
.

post #11 of 19
Quote:
Originally Posted by RAFA View Post

The noise and distortion could really be a problem, but so far the components that I am using do not really consume that much of power. How is it possible for the Sflo2 to be without distortion with low noise and having 2 DACs + opamp all powered by a 3.7v battery.

 

In the end I cannot say exactly that all this will work, but I will try :D

Consider a portable such as the Sansa Fuze.  Each of the line outputs have +1.2vdc thus requiring blocking caps for the external headphone amp.  This implies that most of the circuitry runs from the battery, not a differential supply.  I think only the phone driver chips have charge pumps or some design to eliminate large coupling capacitors.  These phone chips in portable devices work well but are compromised from the hi-fi point of view.

post #12 of 19
I think this is rather ambitious for someone of your level of knowledge/experience. cobbling a heap of modules together will not yield good results. if you want to actually achieve better audio than what you can already buy for less money than diy will cost, then you have a lot of research to do. People hesitated to answer for the same reason I hesitated, you have so very little work done and its a lot of work to help.

• charge pumps without further regulation will cause significant noise, far too significant to use for an analogue dac supply. using 2 x 3.7v batteries in series for 7.4+v and then regulating that down is a better solution, but you must monitor voltage and have automatic shutdown with lipo or you risk a fire. I would be very careful buying cheap lipos, they can not only be dangerous, but can also misrepresent capacity.

• the tpa6120A is very sensitive to board layout as its very fast wide bandwidth chip, it was initially designed for ADSL, it also cannot be hand soldered without a custom PCB as it needs the powerpad underneath soldered very well to have any heatsinking.

• I think you have also underestimated how much power this is going to use, particularly that chip. have you worked out a power budget?

• why regulate down to 3.3v and then step it up again to 5v? thats a big waste of energy

• where are your clocks? yes plural, you will need at least one for the audio and then one for the i2C or MCU . clock layout and routing is not trivial and radiates noise like RF. dont tell me you are using the crappy PLL derived clock from the STM32 and not even reclocking it before using it as i2s and masterclock? the jitter will be very high.

• you must decide the clock and sample rates you will handle before you can work out your power consumption, the dac uses more power when running on a higher clock speed

• the LM780X is old, noisy and inefficient; an LDO like lt1764A or lt1963A would be more suitable, or even better if you can do bga type soldering, the TPS7A47 for main regs and several LP8900, or just several TPS7A47 if you can manage it. its quite a neat new reg with very low noise for an IC reg and up to 1A current with the right PCB

• what headphones are you using with this? without some feedback tricks, the basic datasheet implementation of the TPA6120A has too high output impedance for IEMs this is at the center of complaints that the fostex iHPx is lacking bass response with IEMs

before you go further though, what are you doing that cannot be had commercially? do not make the mistake of thinking this will save you money, that would be a terrible reason to do this project and is unlikely to be the case, with your chosen parts you cannot hope to do better than what is already available, so the only reason to do this would be for the learning and bragging rights, but you can only brag if it works.

Eagle is fine, but i'm not sure if its capable of 4 layer unless you buy one of the higher priced versions

good luck
Edited by qusp - 10/6/12 at 11:40pm
post #13 of 19
make sure to isolate the supplies with ferrite beads so the digital does not contaminate the analogue sections. you can also add small value resistors between the supplies to stop noise currents running over the board. ground layout will be critical
post #14 of 19

+5VDC and +3,3VDC from standard COTS laptop supply (+9VDC to +18VDC). Design fully tested!

 

LiFePO4 Battery (HY2112 is BMS) + USB-Charger + PowerPath (for +3,3VSTDB). Fully tested!

post #15 of 19
Thread Starter 
Quote:
Originally Posted by fubar3 View Post

Consider a portable such as the Sansa Fuze.  Each of the line outputs have +1.2vdc thus requiring blocking caps for the external headphone amp.  This implies that most of the circuitry runs from the battery, not a differential supply.  I think only the phone driver chips have charge pumps or some design to eliminate large coupling capacitors.  These phone chips in portable devices work well but are compromised from the hi-fi point of view.

 

Yep they are. The TPA6130A2 I wantd to use, has siilarities with the MAX9722 from the Cube C30 player. It is a little mor than the Sansa Fuze power. Personally I felt that the only thing that the C30 lacked was a decent DAC inside, everything else was fine.

 

Quote:
Originally Posted by qusp View Post

make sure to isolate the supplies with ferrite beads so the digital does not contaminate the analogue sections. you can also add small value resistors between the supplies to stop noise currents running over the board. ground layout will be critical

 

Thank you qusp. So it seems that I have to go right back to the books. Now I feel bad that I actually wanted to use the STM32 PLL.

 

Seriously I will start off from the battery circuit, it seems to be the most important part for now.

 

At the moment I am at Chapter 6 from "The Art of Electronics" from Horowitz and Hill -> Voltage regulators and power circuits. I read in 2 or 3 forums, that this is the book, when you want to learn electronics and start off.

 

The project itself is just a hobby for me and open for all, since people here have a variety of DIY-amps to choose from, but do not have any decent DIY-dap to choose from. However thanks again.


Edited by RAFA - 10/7/12 at 1:53am
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