LM4867MT NOPB National Semiconductor, LM4867MT NOPB Datasheet - Page 12

• Manufacturer Part Number: LM4867MT NOPB
• Manufacturer: National Semiconductor

Typical Performance Characteristics
External Components Description
Application Information
ELIMINATING OUTPUT COUPLING CAPACITORS
Typical single-supply audio amplifiers that can switch be-
tween driving bridge-tied-load (BTL) speakers and single-
ended (SE) headphones use a coupling capacitor on each
SE output. This capacitor blocks the half-supply voltage to
Components
Figure 1
1.
2.
3.
4.
5.
C
C
R
R
C
B
s
i
i
f
Inverting input resistance which sets the closed-loop gain in conjunction with R
high pass filter with C
Input coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. Also creates a
highpass filter with R
for an explanation of how to determine the value of C
Feedback resistance which sets the closed-loop gain in conjunction with R
Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing
section for information concerning proper placement and selection of the supply bypass capacitor.
Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper Selection of
External Components, for information concerning proper placement and selection of C
Supply Current vs
Rejection Ratio
Supply Voltage
Power Supply
i
at f
i
at f
20001323
c
20001321
c
= 1/(2πR
= 1/(2πR
i
C
i
C
i
). Refer to the section, Proper Selection of External Components,
i
).
Functional Description
11
(Continued)
which the output amplifiers are typically biased and couples
the audio signal to the headphones. The signal return to
circuit ground is through the headphone jack’s sleeve.
The LM4867 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
headphones. The headphones operate in a manner very
similar to a bridge-tied-load (BTL). The same DC voltage is
i
.
Frequency Response
Open Loop
i
.
f
DD
. This resistor also forms a
/2 to a stereo headphone
B
.
20001322
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