Hi all!
I'm not sure if this belongs on this forum, but I couldn't get much help anywhere else.
I am designing an audio amplifier based on the TPA3255 from Texas Instruments.
How would I size the heatsink?
Datasheet:
Thanks in advance!
EDIT: The input voltage is 51VDC, the output watts is 600W@4Ω.
Roughly speaking you want to figure out the amount of power to be dissipated (Figure 9 in datasheet gives efficiency vs output power (about 90% @ 600W implies about 60 W for continuous max output)) and the allowable temperature rise at the heat sink (call it about 60 C) which implies a heat sink rated at 1 C/W. This would be a very very serious passive heat sink.
If we're doing audio or music rather than a continuous peak signal, the amplifier average power is much less than the continuous peak power, so we can safely de-rate. Something on the order of /4 or /8 which gets to heat sink rated at 4-8 C/W which is reasonable.
Keep in mind that the TPA3255 has thermal protection, so it should not self-destruct if thermal management is insufficient, but it will distort.
Thanks @killzone_kid and @MrMark !
I found this heatsink in your link @killzone_kid :
Do the specs on this heatsink look right @MrMark ? It says that the heatsink has 2.2˚C/W with 1M/S air flowing across it. I would rather there be no fan at all, but would ~1foot/S be ok still?
Thanks!
Make sure you buy a genuine chip from reputable seller, knockoffs can not only have subpar audio characteristics but the thermal as well
Yeah, I've realized that after a lot of failed projects due to after-market parts 
.
Here's the product link:
I'm buying directly from TI.com .
Thermally that should be more than adequate, I haven't checked to see if it's mechanically compatible with the package.
You could have a temperature sensor controlled fan (Arduino relevance 
) that only kicks in when the heat sink temperature exceeds some threshold temperature.
What is the application? Typically audio amplifiers' average power (which is what matters from a thermal standpoint) is much lower than peak power. Exceptions might include sirens or guitar amplifiers driven deep into distortion.
Great!
It is. It is the heatsink that TI says they use.
Haha. I am already adding an Attiny261 for IR controlling, so I could add a fan setup with that. What temp sensor could I use? The temperature can get pretty hot, so is a thermistor fine? And how would I attach it to the heatsink (not duck tape or hot glue 
)?
A HiFi audio system for in my house. So it definitely won't be at max power 95% of the time.
Thanks again.
There are thermistors packaged with an eyelet that could be attached with one of the bolts holding down the heat sink assembly.
The TPA3255 also has a digital over temperature warning pin that could be monitored as a fail-safe.
Is this one good?