my experience so far with the TI dc-dc

Post by **Skyone** » Tue Mar 28, 2006 9:31 pm

@Tim: Personally, I WOULD THINK that it could handle 10v, because it goes through 7805s, BUT, according to the stickies, it can only handle up to 9v.

timmeh87 · Post by **timmeh87** » Tue Mar 28, 2006 9:32 pm

the 7805s should be able to handle up to like 25 volts. i think there might be a chip on there that takes unregulated power or something.

Post by **Skyone** » Tue Mar 28, 2006 9:39 pm

Ya, they can handle 32v @ 1.5A.

And according to the board, the 7.2v-9v goes into a few SMD apps, and into a chip or two, so you're best off with 7.2v-9v.

timmeh87 · Post by **timmeh87** » Tue Mar 28, 2006 9:44 pm

well, i suspect it should work at 9v anyways.

the power supply only does 1.5a max though. i hope it will have enough power...

Post by **marshallh** » Tue Mar 28, 2006 9:58 pm

Ok, we've finally got the man on this.

I've got the same results you have:

N64: Wall - LCD: Wall
Perfect, of course.

N64: Wall - LCD: Battery
N64: Batt - LCD: Wall
Great image. DC-DC pulls through fine.

N64: Batt - LCD: Battery
Noticable diagonal lines. No relation to cpu load.
However, if I have the N64's video out hooked up to a TV and the Psone LCD-
I get a fine image running both N64 and LCD off same battery, but without composite video connected. TV looks fine.
When I connect composite to the LCD (which is already running) I get the interference.

So, somewhere the regulator is screwing with the video signal. I don't think its becuase of groud loop interference, I've tried lots of different grounding schemes.

Tim, I think you're getting bad distortion becuase your battery can't handle the current draw. My 7.4v DVD player battery works fine, but the distortion gets unreadable when the voltage drops (N64 is fine, still gets 3.3v but psone lcd doesn't work)

Post by **Skyone** » Tue Mar 28, 2006 10:12 pm

Marshall, what is the mAh rating of your battery?

daguuy · Post by **daguuy** » Tue Mar 28, 2006 10:15 pm

is this problem just with official psone screens? has anybody had any experience with other non-official 5" screens? back when my psone screen worked, i ran it and the N64 from my 8.4v 4200mah battery and it worked fine with some diagonal lines but nothing serious. i played it for about a half hour and then it got extremely distorted and un playable. then i charged the battery and it worked again. i don't see why it would do that because my battery has higher volatage and amp hours than most of the batteries you guys are using

superdeformed · Post by **superdeformed** » Tue Mar 28, 2006 10:21 pm

According to the datasheet of the encoder the "absolute max" is 8.5 volts (for VCC2; normal range is 7-8V), but I'd imagine that's just the max for desired operation. Any higher than that and you start getting a lot of distortion, and from my experiance anything above 9V is completely unusable (darn unregulated power supplies). The encoder is pretty much powered directly off of the 7.5V input aside from going through a few small inductors for isolation, so I'd say 9 volts as a limit to avoid frying the thing.

timmeh87 · Post by **timmeh87** » Tue Mar 28, 2006 11:29 pm

the mah rating of your battery is not related to the max current it will provide. thats determined by the size of the cell and its internal resistance.

daguuy, it sounds like the distortion was happening because the voltage on your batteries was dropping below a certain theshold. which goes along with the "converter dosent work proerly because of votlage" theory.

marhsall, the batteries im using are just crap little temporary ones i found lying around the office.. they've appeared in pictures before. id not be surprised if they couldnt give me the 2A+ that i need. (2A is more than C for these cells) the cells i plan on using the in the final design are rated up to 5A though.

im going to search TI.com for a better converter

Score:
http://focus.ti.com/docs/prod/folders/p ... 8080w.html

im getting me one of these.

well the 8080s are out of stock, but they have 8000's (which appear to be identical in every way) but TI wont let me order any more samples! lol. i guess they think ive had enough. only a minor issue, ill get one of my friends on the team to do it.

Post by **marshallh** » Wed Mar 29, 2006 7:10 am

anotherperson: I ran my DVD player all the way down (not good to do) and the DC-DC kept on working down to about 6.5volts. The N64 was still running fine, but the PSone screen gets unusable because it needs at least 7.1v to function

XFactor · Post by **XFactor** » Wed Mar 29, 2006 7:23 am

I just ordered the one that tim's talking about. It should arrive Friday.

Does anyone know what this new converter requires in order to run? The description says that you need resistors to step down the voltage; but which value of a resistor i do not know (you also look like you need a capacitor). I tried to open the datasheet, but firefox hates PDFs...

vb_master · Post by **vb_master** » Wed Mar 29, 2006 7:42 am

What if you use two? One for LCD and one for system?

timmeh87 · Post by **timmeh87** » Wed Mar 29, 2006 8:51 am

vb_master: what do you mean?... why does the screen need one. anotherperson is probably right.

xfactor: ill look into it later, i have to leave for school now... use internet explorer, its definitely in the datasheet. and the resistor dosent "drop the voltage", it just tells the microcontroller what voltage you want it to output.

vb_master · Post by **vb_master** » Wed Mar 29, 2006 9:02 am

Yeah, that's what I was saying.

Post by **Skyone** » Wed Mar 29, 2006 5:02 pm

So you think I SHOULD be safe with a 8.4 battery?