case when a BTL is connected to the amplifier, the compara-

tor forces the LM4840 to maintain bridged−amplifier opera-

tion. When the HP−Sense pin is externally floated, such as

when headphones are connected to the jack shown in

Figure

2, and internal pull−up forces V

tor’s HP−Sense inputs. This changes the comparator’s out-

put state and enables the headphone function: it turns off

Amp2B, switches Amp2A’s input signal from an audio signal

to the V

bridge-connected loads. Amp1A and Amp1B drive the head-

phones.

Figure 2 also shows the suggested headphone jack electri-

cal connections. The jack is designed to mate with a

three−wire plug. The plug’s tip and ring should each carry

one of the two stereo output signals, whereas the sleeve

provides the return to Amp2A. A headphone jack with one

control pin contact is sufficient to drive the HP−Sense pin

when connecting headphones.

A switch can replace the headphone jack contact pin. When

a switch shorts the HP−Sense pin to V

speakers are muted and Amp1A and Amp2A drive a pair of

headphones. When a switch shorts the HP−Sense pin to

GND, the LM4840 operates in bridge mode. If headphone

drive is not needed, short the HP−Sense pin to the −OUTB

pin.

DS200104-74

FIGURE 2. The ESDAxxxL provides additional ESD protection beyond the 8000V shown in the Absolute Maximum

Ratings for the AMP2A output

DS200104-75

FIGURE 3. Volume Control Timing Diagram

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