TI TPA3112d1 any good?

[NebuK]

Heyyas,

after i've read quite some literature on DIY Amps, finally managed to build my first Class-AB chipamp i wanted to try fooling around with Class-D stuff a bit. For this i've searched around for low power Class-D chips that don't need too much external components and have a little power at least. I've found the TexasInstruments TPA3112d1 - which has 25W into 8Ohms with <0.1% THD+N @ 24v... sounds reasonable.

ds: http://focus.ti.com/lit/ds/symlink/tpa3112d1.pdf

Browsing the datasheet i've found a okay SNR but the K_VSR (excuse my beginners talk, but .. is this roughly the PSRR?) sounds a bit wrong with only -70dB - is that right?

Anyways, what do you guys think - would this little chip (given that i could solder it ... gotta train a little oO) be a nice first Class-D project? Or did i miss something bad in the datasheet that makes it totally unuseable for HiFi/"a-little-higher"-end applications?

Thanks in Advance, Kind Regards
- NebuK

[Hitec]

Note that it is designed to be soldered on a thermal pad. It is also quite fine-pitched. Otherwise it looks like a nice starting point for a small amplifier.

I have been using NXP TDA8920 which is bigger and through-hole versions available. It doesn't need a lot of external components.

[killerbobjr]

You're much better off with the TPA3122D2. It's in a 20 pin DIP package which makes it super easy to use in a breadboard or solderable perfboard. The application schematic in the datasheet is almost complete -- just attach a 10K resistor from VCC to /SD and MUTE to ground for a minimal circuit.

[NebuK]

Heyyas,

the NXP TDA8920 looks interesting and nice - but problem's the availability here in germany. As for the TI chips i could sample them if available or order at mouser for only small shipping costs (as far as i checked it)... If you have a good source, please share!

The 3122D2 also looks nice, a 20Pin PDIP would be lovely . The only backdraw i could see right now is that it only delivers 8W into 8Ohms at 1% THD+N whereas the D1 delivers - if i'm not mistaken (please bear with me, i'm still new to this stuff and tend to overlook datasheet details oO) - 25W at < 0.1% THD+N into 8Ohms, which is more like the power i was looking for. After all i want to use this little baby even if it's primary purpose is learning/training ...

Did i overlook some thd/power details here? Anyways, what does experience say about that extremely fine-pitch stuff with a thermal pad hack like "hey, lets make a copper pad there, drill a hole, fill it with solder, solder the chip (if it works oO) and then fill the hole with solder from the bottomside ... not exactly what the PowerPAD(TM)(R) quickstart says but that would sound closest to what a newbie like me expects to "could-maybe-work" in a home environment...

Thanks alot for the answers! Kind Regards
- NebuK

PS: Sorry for the bad english! My skills got a bit rusty ... ;/

[killerbobjr]

The only difference between the various TI TPA31xx class-D medium power chips is their thermal rating. They are actually all the same piece of silicon, just in different packages. You can glue a heatsink to any of them and get the same thermal derating.

The TPA3122D2 can take a recommended maximum VCC of 30V and will put out ~47W into a bridged 8 ohm load. It has built in thermal protection (rated 150C trip point), so you couldn't overheat it if you wanted to.

A really easy heat sink is to mount the DIP chip underneath your PCB with all the rest of the components on top, then mount the PCB on a chassis so the DIP package contacts it (an aluminum plate in a project box will do nicely).

[NebuK]

Uh, that is one valueable information! Thanks!

But still after reading the datasheets twice and again side-by-side i'm somehownot sure whether the only differences are *really* thermal ratings. Again here, i'm quite a newbie, so i'm begging to correct me and throw information at me . But where the D1 delivers a THD+N of <= 0.1% at 25W the D2 shoots the THD up to 10% at 10W - sure, those aren't the BTL values (are they even noted anywhere?), but i somehow can't believe that's only thermal rating. And even if - the powerpad seems like it can dissipate much more heat quicker from the die to the thermal pad than a DIP ever could ... am i really okay with only a vastly overdimensioned heatsink? I'm just a little scared that i put quite some time into building a -D2 solution and then it gives me horrible THDs already at quite "low" power output ...

Anyways, thank you alot for your answers!
Kind Regards
- Dario Ernst

PS: am i right in that the "filter-free" solution with a ferrite-bead mentioned in the -D1 datasheet is b*s for HiFi/"a-little-higher-end" applications? As far as i understand a filter-design would gain more efficiency and doesn't use the hack of using the cables and speakers themselves as filters... right?

[killerbobjr]

Your 10% THD figures are totally dependent on VCC. As long as the peak output doesn't saturate the rails, the distortion figures will remain well below 1%. If we assume a 90% efficiency, then 12V VCC gives 10.8V P-P across a load. That's approximately 3.6W peak/2.6W RMS for 8 ohms single ended mode. At 24V VCC, you get 21.6V P-P and approx. 14.6W peak/10.3W RMS. If you look at the TPA3122D2 data sheet, figure 6., you'll see that the 10% distortion figure pretty much matches these calculations. Of course the efficiency level changes with power output (figure 14.), so you'd have to take that into account when making final calculations.

Even at peak power in BTL mode, these chips won't dissipate more than a few watts, so I wouldn't worry too much about heatsinking.

The switching frequency of the TPA3112D1 is at 310KHz median vs. the TPA3122D2 250KHz median which isn't a whole lot of difference. The use of bead filters is merely an economical trade off for low cost applications. If you want good filtering with proper loading, you're going to have to go with a standard LC filter.

[Zaaphod]

Originally Posted by NebuK

But still after reading the datasheets twice and again side-by-side i'm somehownot sure whether the only differences are *really* thermal ratings. Again here, i'm quite a newbie, so i'm begging to correct me and throw information at me . But where the D1 delivers a THD+N of <= 0.1% at 25W the D2 shoots the THD up to 10% at 10W - sure, those aren't the BTL values

They are marketing the TPA3122D2 as a stereo chip and all the ratings are based on using it in stereo mode, while they are marketing the TPA3112D1 as a mono chip with a BTL output.. so comparing the distortion ratings and power graphs etc, you are not really looking at the same thing. Comparing apples to oranges so to speak.

I really really like that DIP package!! I'm sure I can learn how to solder surface mount stuff, but I'd prefer to put that off for a little while. and it would be great to be able to breadboard my prototype and use IC sockets for preliminary designs. Has anyone else built an amp based on the TPA3122D2? I think I'd like to try it out.. any suggestions would be appreciated.