LM4868MT National Semiconductor, LM4868MT Datasheet - Page 11

• Manufacturer Part Number: LM4868MT
• Description: Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function
• Manufacturer: National Semiconductor

Typical Performance Characteristics
Application Information
ELIMINATING OUTPUT COUPLING CAPACITORS
Typical single-supply audio amplifiers that can switch be-
tween
single-ended (SE) headphones use a coupling capacitor on
each SE output. This capacitor blocks the half-supply volt-
age to which the output amplifiers are typically biased and
Components
( Refer to Figure 1. )
1.
2.
3.
4.
5.
driving
C
C
R
R
C
B
s
i
i
f
This is the inverting input resistance that sets the closed-loop gain in conjunction with R
forms a high pass filter with C
This is the input coupling capacitor. It blocks the DC voltage at the amplifier’s input terminals. It also
creates a highpass filter with R
for an explanation of how to determine the value of C
This is the feedback resistance. It sets the closed-loop gain in conjunction with R
This is the supply bypass capacitor. It provides power supply filtering. Refer to the Power Supply
Bypassing section for information concerning proper placement and selection of the supply bypass
capacitor.
This is the bypass pin capacitor. It provides half-supply filtering. Refer to the section, Proper Selection of
External Components, for information concerning proper placement and selection of C
bridge-tied-load
Supply Current vs
Rejection Ratio
Supply Voltage
Power Supply
(BTL)
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speakers
External Components Description
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i
i
at f
at f
c
c
= 1/(2πR
= 1/(2πR
and
Functional Description
i
C
i
11
C
(Continued)
i
).
i
). Refer to the section, Selecting External Components,
couples the audio signal to the headphones. The signal
return to circuit ground is through the headphone jack’s
sleeve.
The LM4868 eliminates these coupling capacitors. Amp2A is
internally configured to apply V
jack’s sleeve. This voltage matches the quiescent voltage
present on the Amp1A and Amp1B outputs that drive the
i
.
Frequency Response
Open Loop
i
.
DD
/2 to a stereo headphone
f
B
. This resistor also
.
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