TPA3132D2 won't make a peep! - Page 1
Forum section: electronics / projects

author: sswift
author_rank: Contributor
timestamp: April 12, 2016, 09:15:54 pm
content: Hey guys,So I made this board which has a built in 40W amplifier:Actually, I made two versions of it. The first version worked great. For the second version pictured here however I altered the design slightly and it doesn't work at all, and I can't figure out what's wrong.What I do know is that the portions of my circuit which are producing the sound effects to play through the amplifier are working fine all the way up to the amplifier's input. I checked this by connecting the output of the last capacitor before the input to the amplifier at pin 31 to another amplifier. It sounded fine. So the issue almost certainly is the amplifier itself.I also had two copies of this board manufactured. Neither work. So it is unlikely to be a random solder bridge.I also checked that the chip was rotated to the correct orientation. It is.I also probed the speaker outputs with a multimeter just in case I had a bad speaker hooked up. Zero volts there.I hear no pop or anything from the speaker when I power the board up. That's good but it also tells me nothing about what might be going wrong.Here is the datasheet for the amp:http://www.ti.com/lit/ds/symlink/tpa3132d2.pdfAnd here are the schematics and layout of the version pictured which doesn't work:And these are the schematics of the version which did work:The only thing I really changed between the two is the resistors used to choose the gain. On the new/bad layout I changed the gain to 20db which required only a single resistor.

author: moffy
author_rank: Super Contributor
timestamp: April 12, 2016, 11:52:09 pm
content: Try bridging a 28k resistor between the 5.6k/GAIN pin and GVDD, that should give you the same 26db gain of before. Just as a test to see if it works. It should be safe to use a DMM to measure the resistance with power OFF to the circuit.

author: sswift
author_rank: Contributor
timestamp: April 13, 2016, 08:24:14 pm
content: Well I've measured the resistors on both boards and they're both 5.66K so that's not the problem. :/I really don't want to muck up the board by soldering another resistor on there if I can help it. There's no reason I can think of why 20db shouldn't work but 26db does. The volume was not really low or anything when I tested with the other amp. It's gotta be some other issue.

author: PChi
author_rank: Frequent Contributor
timestamp: April 13, 2016, 08:39:24 pm
content: As an outside chance is the protection circuit continually operating? It may be worth probing the FAULTZ pin.

author: David_AVD
author_rank: Super Contributor
timestamp: April 13, 2016, 08:43:23 pm
content: Where is the pullup on pins 29/30 ? You can't leave it floating.

author: sswift
author_rank: Contributor
timestamp: April 13, 2016, 09:50:44 pm
content: Quote from: David_AVD on April 13, 2016, 08:43:23 pmIt's not floating.http://www.ti.com/lit/ds/symlink/tpa3132d2.pdfPage 16:QuoteAnd page 4:QuoteSo, FAULTZ should be high by default, which pulls SDZ high, which enables the outputs. If FAULTZ goes low, it pulls SDZ low, disabling the outputs until the fault condition (such as shorting the outputs) clears.

author: sswift
author_rank: Contributor
timestamp: April 13, 2016, 10:07:03 pm
content: Quote from: PChi on April 13, 2016, 08:39:24 pmGood idea, I'll try that.Hm... I made my best attempt to probe those tiny pins and I'm reading 0.76V? That's not right.Also I think I accidentally shorted the speaker input pins to it for a moment, which caused the speaker to pop.I guess I'll solder together a probe with a resistor on it so I can try pulling that pin up and see what happens. But even if it works... it shouldn't. FAULTZ ought to go low when there is a fault and high when there isn't. There isn't any mention of an internal resistor on that pin either so it ought to override any pullup I put on there. In addition, even if it works, do I have a fault condition, or don't I? If I don't I shouldn't need the pullup, if I do I shouldn't be able to nor should I override it.

author: sswift
author_rank: Contributor
timestamp: April 13, 2016, 10:38:39 pm
content: Well, David was apparently right about needing a pullup. I'm getting audio with one in place! But according to the datasheet, I shouldn't need one. :/And the last two of these I manufactured with a slightly different layout worked fine without one as well.

author: David_AVD
author_rank: Super Contributor
timestamp: April 13, 2016, 11:38:46 pm
content: The fault pin is open collector (or drain) so doesn't provide any voltage source. You need the pull-up.The idea is that you can use a micro pin to read the pin 29/30 combo and if it's low then the amp is in fault mode. You can also use the micro to force the pin pair low to shut the chip down.

author: sswift
author_rank: Contributor
timestamp: April 14, 2016, 12:18:03 am
content: Quote from: David_AVD on April 13, 2016, 11:38:46 pmI get that now, but how was I supposed to know that from the datasheet?I see that they have a pullup on the application schematic on page 21, but the pin definitions clearly state that FAULTZ is an output and is high during normal operation. The datasheet also states that to enable automatic recovery one should short FAULTZ to SDZ and there is no mention of a pullup. :/Well... hopefully I can solder a tiny resistor between those pins and the PVCC pins that are conveniently located next to them so I can get this thing up and running.

author: David_AVD
author_rank: Super Contributor
timestamp: April 14, 2016, 03:43:34 am
content: Check section 6.3 of the data sheet. It mentions the pull-up there. I agree that it's not super obvious at first glance.

author: sswift
author_rank: Contributor
timestamp: April 14, 2016, 06:06:41 am
content: Quote from: David_AVD on April 14, 2016, 03:43:34 amWell yeah I see that, but that's just telling me what that spec will be with that condition, it's not saying it'srequired.I mean I guess I can see how it MIGHT be possible to come to the conclusion that a pull up is required on that pin taking the totality of the data sheet into account but that's hardly fair of them to expect people to puzzle out something as basic as that feature by looking at multiple schematics and the section on how to interface it with a microcontroller which I'm not doing so of course I just skimmed that section without trying to fully understand it.Anyway, thanks for the help!