MAX9720 - 50mW, DirectDrive, Stereo Headphone Amplifier with SmartSense and Shutdown

The MAX9720 stereo headphone amplifier combines
Maxim’s patented DirectDrive architecture and
SmartSense™, an automatic mono/stereo detection feature.
Conventional headphone amplifiers require a bulky
DC-blocking capacitor between the headphone and the
amplifier. DirectDrive produces a ground-referenced output
from a single supply, eliminating the need for large
DC-blocking capacitors, saving cost, board space, and
component height.

SmartSense automatically detects the presence of a
short at either the left or right amplifier output. Under a
fault condition, the shorted output is automatically disabled
and the stereo input signal is automatically mixed
and routed to the remaining active channel. This feature
is useful in cell phone and PDA applications where a
variety of headphone jacks with unknown loads can be
inserted into the headphone jack socket. SmartSense
prevents both damage to the amplifier and eliminates
battery drain into a shorted load.
The MAX9720 delivers up to 50mW per channel into a
16Ω load and has an ultra-low 0.003% THD+N. A high
(92dB at 217kHz) power-supply rejection ratio (PSRR)
allows the device to operate from noisy digital supplies
without additional power conditioning. The gain of the
MAX9720 is set internally, further reducing component
count. Two gain options are available (-1V/V, MAX9720A
and -1.41V/V, MAX9720B). The headphone outputs
include a comprehensive click-and-pop circuitry that
eliminates audible glitches on startup and shutdown. A
shutdown mode provides a fast 250μs turn-on time.
The MAX9720 operates from a single 1.8V to 3.6V
supply and consumes only 5mA of supply current. The
MAX9720 also features thermal overload protection,
and is specified over the extended -40°C to +85°C temperature
range. The MAX9720 is available in a tiny
(2mm x 2mm x 0.6mm) 16-bump chip-scale package
(UCSP&trade and a 16-pin TSSOP package.