lm4840 National Semiconductor Corporation, lm4840 Datasheet - Page 13

• Manufacturer Part Number: lm4840
• Description: Stereo 2w Audio Power Amplifiers With Digital Volume Control And Input Mux
• Manufacturer: National Semiconductor Corporation

Application Information
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
FIGURE 2. The ESDAxxxL provides additional ESD protection beyond the 8000V shown in the Absolute Maximum
DD
/2 voltage present on pin 14, and mutes the
DD
on the internal compara-
FIGURE 3. Volume Control Timing Diagram
(Continued)
Ratings for the AMP2A output
13
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
DS200104-75
DD
, bridge−connected
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