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 Post subject: ti's little white one
PostPosted: Sat Jul 18, 2009 1:01 am 
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http://www.planetanalog.com/showArticle ... =165702856

:cry:

It's not so much a misperception when they've commonly been rather slack in control, prefering the simpler and cheaper "open loop", which is absurd. But no, don't talk about zero PSRR or anything, give them the red herring of saturation and clipping behavior instead.

Maybe even whine about how Tact millenium was audiophile.. when playing Diana Krall? Oh and tell me again about how they've brought down the price, now everybody has at least one :wave:

"Past articles from EE Times have suggested that all Class D amplifiers are a challenge to implement. However, with new features, such as intelligent gate drive and two-stage over-current (OC) detection, makes it easier to design with a digital amplifier. Intelligent gate drive relaxes layout and placement issues that previously were critical to passing EMI suppression requirements. ..."

Past articles from EE Times have been less full of shit. Can you be more misinformed? TI is hungry to pump out chips to china so they're trying to downplay the basic realities of the damn things which if they succeed should help to push class d back another whole decade. "Intelligent gate drive", they've barely had one that works decent yet, but now it seems they'd have you believe they've invented a new realm of physics that negates the need for a proper high speed low parasitic board layout at critical nodes in high speed power switching circuits.... :rotfl:

That's why people using their any-fool-can-do ICs have to circumvent the OC because it falsely trips with anything less than the ideal layout. Oh yeah, the B version introduced a leading edge blanking zone, we can wire it in p2p now. Forget passing EMI suppression requirements, you've barely achieved basic functionality, and here you are selling your relaxed requirements, damn.

"...Since a digital amplifier places a high DC voltage directly across the speaker"

Oh is that what they do? :rolleyes: Stick a fork in it, and go back to marketing management class.

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PostPosted: Wed Jul 22, 2009 8:09 pm 
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I've used a couple of their open-loop, analog-in parts over the years: TPA3123 for a voice amplifier that ran off a 24V wheelchair battery, and a TPA3100 for a solar powered radio for camping. Never had any issues with either part, but efficiency rather than audio quality was the design criteria.

That being said, I wouldn't use one of their digital input class-D's. Throwing "closed loop" on the chip description and not showing anything about where or how it's implemented in the actual IC isn't something I like. Could be a load of baloney for all I know...


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PostPosted: Thu Jul 23, 2009 1:45 pm 
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TI and IR both seem to make similarly absurd marketing statements, probably to compete with each other, but I'm not sure who or what it's helping. They've all pumped out some real junk in relation to class d as well.

None the less, TI's new Purepath part looks respectable, and the datasheet for it indicates they recognize otherwise in terms of layout.

They've seemingly integrated the entire output stage, so it may also be easier for anybody to slap together, but there's still several key areas you can screw it up, and they usually do.. but what more could you expect from a system that caters to unskilled mass production lines.

I still have to call bullshit on their recommended 33nF bootstrap cap though.

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PostPosted: Wed Sep 23, 2009 5:54 pm 
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TragicallyDistorted wrote:
"...Since a digital amplifier places a high DC voltage directly across the speaker"

Oh is that what they do?


Hi.

No, more than than. That Planet Analgoue article further stated that "considering that a speakers impedance is frequently dependent, it can be difficult to differentiate btween an impedance drop and a true SHORT CIRCUIT condition."

First off, no loudspeaker ever gets a momentary impedance drop down to zero ohm long enough to be seen by a loudspeaker amp as a "true short circuit condition". Otherwise, it will be a disaster for any analogue amps, tube or bipolar, to handle, long before the era of digital amps.

I don't know whether it is the erroneous comment of the author of this article or the actual statement in the orginal article: "The true about Class D amplifiers".

In either case, whoever published such absurb statement should go back to learn more about loudspeaker analogue performance data before jumping onto the digital wagon.

c-J

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