Bridging the output of speaker

Thanks for inquiring about the MAX98306.

Unfortunately, the MAX98306 was not designed for mono-bridged outputs and is not a supported use case.

Hi Mike,

My aim is to drive 5W into 4Ω load. I can supply 5V at more.

MAX98307 can drive  8Ω + 68μH Load with 3.3W at VPVDD = 5V.

However, I have 4Ω-5W speaker and desire to achieve 4.5-5W. 

Is it suitable to use MAX98307 to drive my speaker.

And how should i calculate power then ? With P=Vrms^2/R   ? 

Thank you.

Cevdet.

Cevdet,

The MAX98307 won't get you to a 5W either.  That amplifier appears to be thermally limited with 4Ω @ 5V.

You're right about the power.  It is just VRMS^2/R.  So, for a 5V supply, that would give you a maximum output swing of 5V/sqrt(2) = 3.54VRMS.  Plugging in for 4Ω and you'd get a theoretical (ideal) output power of 3.125W.   You can see that point on this plot:

In this case, the theoretical output power for 5V supply with 4Ω is right above the 10% THD+N value on the plot which is expected.   This will be true for all class-D amplifiers.  Real world performance is lower based on factors like output impedance of the amplifier, maximum current limit and thermal limit.

Most amplifiers like these have limited output power primarily due to the supply voltage range and sometimes the thermal limit.  To move up in power you'll need a slightly larger power supply voltage.

Take a look at the MAX98400B.  I think it would meet your needs:

MAX98400A/MAX98400B - Stereo, High-Power, Class D Amplifiers (analog.com)

Dear Mike,

I deeply apricated your fast response.

The graph screenshot is belong to MAX98306. However I asked for  MAX98307. Are they equal ? Or you only used for illustration. 

About MAX98400A, It has min 8V. I have 5V system supply. And cannot afford to have another power supply.

I may decrease load to 3Ohm. 

Would you recommend to do that ?

Cevdet.

Cevdet,

The plot was from MAX98306, it was a typo on my part.

MAX98306 is rated for 3Ω and will get you to 3.7W which I would definitely recommend.  It will nearly achieve your target.  Since you're limited to 5V, this is the best output power you'll be able to achieve for a non-boosted class-D amplifier.

If you were to move to a more modern audio amplifier with digital audio input, then we could look at boosted parts like the MAX98380.

MAX98380.pdf (analog.com)