Digital audio amplifier delivers 8+8W stereo from one Li-ion cell


PAM8965 classD amp

Called PAM8965, more detailed figures are:

  • One cell (Vbatt = 3.7V)
    8W/channel at 10% THD+N (6Ω load 1kHz)
    6.4W/channel at 1% THD+N (6Ω load 1kHz)
    20mA quiescent
    700nA shutdown
  • Two cells (7.4V)
    12W/channel at 10% THD+N (4Ω load 1kHz)
    9.6W/channel at 1% THD+N (4Ω load 1kHz)
    10mA quiescent

Integrated output noise of the audio channel at 26dB (max) gain is 70μVrms (A-weighted), and THD+N is 0.035% when delivering 5W.

Unusually in a Class-D amplifier, there is a provision for audio feedback.

“The headlining feature of PAM8965 is the provision of external audio feedback pins,” according to the company. “While internal feedback connection takes care of non-linearities only in the internal feedback loop, the feedback can be Kelvin-connected to the speaker terminals with external feedback pins. This eliminates parasitic resistance and inductance from bond wires, PCB trace, ferrite beads and long speaker leads from adversely affecting the fidelity of the audio signal. Furthermore, the external feedback pins allow the use of filter networks in the feedback path to customize sound without relying on DSP.”

A pin is provided to program audio gain at 0.5dB steps, and the chip uses a 41-step automatic gain control to limit output power without clipping.

Supply voltage can range across 2.8 to 8.5V, and the boost converter output is regulated to 9.2V, operating in PWM mode at mid and high power, shifting to PFM to improve the efficiency at low loads.

“The integrated amplifier can achieve system efficiency of 92% at 7.4V,” according to the company. Shutdown draw is typically 700nA (5μA max).

The boost converter switches outside the audio band (>75kHz) to avoid audible noise from on-board components, and both the converter and amplifiers have spread-spectrum modulation for EMI suppression – allowing ferrite bead filters to be used.

A chopper-enabled integrator in the audio channels typically keeps dc bias across the speakers below 1mV.

Other protections include: Output thermal foldback as the chip heats, complete thermal shutdown above that, battery under-voltage, battery over-voltage, boost over-voltage, audio output short-circuit, Boost output short circuit and cycle-by-cycle boost output current limit. There is a fault flag output.

The PAM8965 product page is here





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