TPA3110D2 Auto-reset at normal volume

[scwhiteley]

Hey out there,

This is my first class D amp project, it's built around the TPA3110D2 IC from Texas Instruments (d/s here) I have essentially used the schematic right from the d/s (fig. 37), with a few embellishments from the evaluation module schematic (evm d/s with schematic here) (i.e. gain control jumpers, adjustable power limit, a ferrite bead on the power supply, not really sure what that's for...). All that aside, the compound schematic I came up and am using for this project is here. I'm powering the unit from a 14.4V NiMH battery pack (12 D cells) and the audio source is my mp3 player (iPod.) Currently, the amp is set up to drive a pair of 4 ohm, 100 W rated power speakers. (4 inch)

My problem is this:
The amp only seems to work at low volume. As soon as I turn the iPod's volume above a third of it's capacity, the amp starts to auto-reset for some reason. After sniffing around on the internet, I am starting to wonder if it is shutting down due to over-current protection as a result of using low impedance (4 ohm) speakers. Does anyone out there have any knowledge of what might be going on here and what I need to do to remedy it? If I had a pair of 8 ohm speakers sitting around, I would have tried that, I'll keep my eyes and ears open for a cheapo pair.

Alternatively, this post leads me to believe that I may be forcing the amp into thermal shutdown. However, according to the d/s, thermal shutdown is not reported on the FAULT pin of the amp, and whatever is going on with my amp definitely is.

THANKS!
-CHAD

PS - As a side question, if you were going to build a class D amp from scratch with similar exterior component parameters, what amp would you go with? Again those parameters are: 14.4 V Battery pack power supply (somewhere around 2000mAH) and either a single mono or a pair of stereo 4 ohm, 100 W rated power speakers.

[sonnya]

Hi CHAD.

The shutdown is quite effective.

I have used the TPA3123 a lot, and i am working with the TPA3110.

They shutdown on overcurrent and overtemperature.

The overtemp is not reported on the \fault pin.

You have to be sure that the powerpad is connected to a large GND plane.

This is taken from the datasheet:

THERMAL PROTECTION
Thermal protection on the TPA3110D2 prevents damage to the device when the internal die temperature
exceeds 150°C. There is a ±15°C tolerance on this trip point from device to device. Once the die temperature
exceeds the thermal set point, the device enters into the shutdown state and the outputs are disabled. This is not
a latched fault. The thermal fault is cleared once the temperature of the die is reduced by 15°C. The device
begins normal operation at this point with no external system interaction.
Thermal protection faults are NOT reported on the FAULT terminal.

[scwhiteley]

Thanks for the reply Sonnya, especially on such an old post.

I've experimented a bit with the TPA3110 chip, with varying results. I think you raise a good point regarding the powerpad connection. Unfortunately, I do all of my work in my dining room, (moving to the garage now that it's getting a little warmer here in Montana.) As such, I've had a real problem soldering the chip down to the pad properly. It's come to the point where I either need to find a cheap, home-brew way to properly solder the chip to the power pad or find a similar class-D amp chip that does not require the powerpad. I would welcome any advice you might have!

Thanks,
Chad

[rikvancoolwijk]

Hi,

I have very good results with the tpa3110d2, getting 30 W sine power from it with ease !
but without the thermal pad on the under site connected it will shut down every second!
I made a pcb with some extra big vias to solder the thermal pad with a normal soldering iron.

Gr Rik

[scwhiteley]

Thanks Gr Rik,

I put some slightly-larger-than-normal vias in the thermal pad on the last experimental amp. After spending an hour trying to get the chip to soak up the solder through the vias with copper wire and an extra hot iron, I gave up without success. As you might imagine, the amp didn't perform, i.e. repeatedly shut down.

When I get my new work area set up I'll try even bigger vias. I suppose I'll just go ahead and make them big enough to fit the end of the iron in (1/32) and make contact with the bottom side of the chip.

Again, thanks for the advice.
Chad

[rikvancoolwijk]

this is what worked for me the big vias are a little les than 1mm.

now i only use solder paste and reflow soldering for smd, less work and cleaner soldering.

Rik

[rikvancoolwijk]

Like this it will work with a normal temp soldering iron and some thin solder.

Rik

[sonnya]

Originally Posted by rikvancoolwijk

Like this it will work with a normal temp soldering iron and some thin solder.

Rik

Yes, he is right about it.

[scwhiteley]

Great, thanks again for the replies.

The TPA3110 seems like the perfect chip for the projects I'm working on, hopefully this will clear up the problems I've been having with it.

Thanks again,
Chad

[rikvancoolwijk]

I hope you'll get it working, else you can pm me for a working module.