save operating voltage for MAX9744

[maddoggarage]

I was successfully running a MAX9744 20W stereo amplifier on a 3-cell Li-Po battery (nominal 11.1VDC). Before showing it to my client, I put a full charge on the battery. When I switched on the battery at the client site, smoke came out of the amplifier chip, and all I got was a high pitched buzzing from the speakers. When I checked the battery voltage with my Fluke 77 meter, I got 12.47VDC. The statistics for the MAX9744 say "Power from 4.5V-14V DC voltage." What is a safe voltage to run this board? Was this a defective board? Will Adafruit send me a replacement? I have photos, but when I try to upload them I get a "photo is invalid" message.

Thank you for your help on this. This is an important client on a tight time frame.

[adafruit_support_mike]

The forum puts a limit on file sizes. 800x600 images usually work best.

The MAX4477 should be able to handle 14v, so the 12.6v full-charge voltage for an 11.1 nominal LiPo should be within its safe operating range.

Post a photo showing the hardware and connections and we'll make sure those are all good.

[maddoggarage]

Here are photos

[maddoggarage]

Oops, I still don't see the photos...

[maddoggarage]

top of board small.JPG (191.27 KiB) Viewed 201 times

prototype board small.JPG (157.38 KiB) Viewed 201 times

[maddoggarage]

burned chip small.JPG (158.81 KiB) Viewed 198 times

finally figured out how to post photos - here is one more

[maddoggarage]

Battery and switch small.JPG (151.15 KiB) Viewed 158 times

Amplifier small.JPG (154.78 KiB) Viewed 158 times

More bad news. My client (Nicolas Gros, La Fabrique) didn't have time to wait for your reply to my postings (I'm still waiting as well) so he ordered another MAX9744. I installed it in the final product (see attached photos of the amplifier and the battery). The amplifier worked fine for two days, then stopped amplifying. No smoke this time, but no sound from the speakers.

[adafruit_support_mike]

Sorry for the delay, we've been tracking a series of issues in this general category.

Two failures in the same environment usually suggests a systemic problem, but right now we're questioning everything.

There is one thing I see in the photos: you've dressed the wire in a couple of coils near the MAX9744, and for the amount of current going through the speakers, it would be possible for the inductance of those coils to generate some flyback voltage.

Send a note to [email protected] with a link to this thread and the folks there will get you a new MAX9744 breakout. Have your client do the same, and we'll provide another replacement or a refund.

When you install the replacement, try connecting a zener diode with a breakdown voltage around 13v in parallel with the supply terminals. Let's see if clamping the supply voltage below 14v makes any difference.

[maddoggarage]

Unfortunately, the project deadline has already passed. We had to use a similar amplifier from another manufacturer, and the circuit has been given to the end user, so I would not be able to test a replacement on this project. I did send a link to support as you suggested.

Thank you for your help.