First and second channel bridge amplifiers are dynamically configured to
drive either speakers or headphones. The first channel bridge amplifier
includes a first amplifier driving one end of a first speaker through a
mechanical switch in a headphone-jack, and a second amplifier driving
another end of the first speaker. The second channel bridge amplifier
includes third and fourth amplifiers driving respective ends of a second
speaker. An amplifier control circuit dynamically detects the insertion
or removal of a plug in the jack and configures the amplifiers
accordingly. When a plug is inserted into the jack, the mechanical switch
disconnects the first speaker from the first amplifier, and the fourth
amplifier is tri-stated disconnect the second speaker. The first and
third amplifiers are configured to drive the first and second channels of
the headphones, while the third amplifier drives the headphone common
point (shield ring) as a virtual ground connection. The virtual ground
connection permits the bridge amplifiers to drive either speakers or
headphones without the use of output coupling capacitors. To suppress
click and pop, the amplifier control circuit maintains certain amplifiers
(depending on headphone or speaker mode) tri-stated until the input
coupling capacitors have fully charged and an input signal is detected.
In the headphone mode, the driving amplifiers are current limited, the
output signal level is automatically attenuated, and the second amplifier
is controlled to prevent a ground loop short circuit condition. When a
ground short is detected, the second amplifier is tri-stated by the
amplifier control circuit.