# Audio amplifier mono operation and power consumption

I'm looking to use a PAM8406 in Class-D mode, with only the left channel active.

The datasheet doesn't discuss how to handle unused pins for the right channel to "deactivate" that half of the amp.

• Should I connect INR, OUTR+ and OUTR- to ground?
• If not, what can I do to ensure the right channel isn't operational?

Additionally, I plan to provide 3.3v to the amp to a 2Ω load, which yields about 2W amplification per chart 17:

• Given 3.3v at 2.2w, this means an amperage draw of about 666mA (not accounting for efficiency, etc), right?

• Is that amperage draw per channel or combined? If it's combined, this means an amperage draw of 333mA in mono mode, correct?

## 2 Answers

Do not connect outputs to ground!

I would connect INR to ground through a resistor and a cap, per their "typical applications schematic". If I were feeling particularly paranoid (which I usually am when going off-datasheet) I would connect an 8$$\\Omega\$$ resistor between OUTR+ and OUTR-. Then I'd cross my fingers and hope the resistor doesn't see much of a turn-on transient (I'd probably back that up with some tests, watching OUTR+ and OUTR- on an oscilloscope while powering up my board).

• Excellent - Thanks a bunch! Question: What would connecting the BTL outputs via a resistor accomplish? – t3ddftw Jul 1 at 20:12
• Probably it would mostly satisfy my paranoia. But some amplifiers are not stable unless they have the right load on the output. If, somewhere in that datasheet, they say that the amp is no-load stable, or if it's designed to be connected to a headphone jack, you're probably OK. – TimWescott Jul 1 at 20:18
• Ah, I thought all amplifiers were stable with no load -- that makes sense :) – t3ddftw Jul 1 at 20:21

I would try a Pi Filter to speaker from each output (L(C//2Ohm)L) to shared speaker so each driver has isolated feedback and LPF to speaker. Then the benefit of this is lower distortion at max power or slightly more power at same max distortion due to lower RdsOn/2 @ 2 Ohm load and reduced reactive power in 2 Ohm speaker at class D frequency.

Otherwise the unused input can be loaded with nothing and inputs inverted to used channel to cancel near-field radiated noise.

But do not connect to Gnd or outputs ganged any other way.

The rated power is for 2 speakers not 1 but the limitation is temp rise and amp distortion , not current that You estimated, I believe at 2 Ohms.