LM4954TLX National Semiconductor, LM4954TLX Datasheet - Page 11

• Manufacturer Part Number: LM4954TLX
• Manufacturer: National Semiconductor

Specifications of LM4954TLX

• Operational Class: Class-AB
• Audio Amplifier Output Configuration: 1-Channel Mono
• Output Power (typ): 1.2x1@8OhmW
• Audio Amplifier Function: Speaker
• Total Harmonic Distortion: 0.1@8Ohm@600mW%
• Single Supply Voltage (typ): 3/5V
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Requirement: Single
• Rail/rail I/o Type: No
• Power Supply Rejection Ratio: 80dB
• Single Supply Voltage (min): 2.7V
• Single Supply Voltage (max): 9V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 9
• Package Type: uSMD
• Lead Free Status / RoHS Status: Not Compliant

Application Information
reproduce signals below 100Hz to 150Hz. Thus, using a
large input capacitor may not increase actual system perfor-
mance.
In addition to system cost and size, click and pop perfor-
mance is affected by the size of the input coupling capacitor,
C
reach its quiescent DC voltage (nominally 1/2V
charge comes from the output via the feedback and is apt to
create pops upon device enable. Thus, by minimizing the
capacitor size based on necessary low frequency response,
turn-on pops can be minimized.
Besides minimizing the input capacitor size, careful consid-
eration should be paid to the bypass capacitor value. Choos-
ing C
range of 0.1µF to 0.39µF), should produce a virtually click-
less and popless shutdown function. While the device will
function properly, (no oscillations or motorboating), with C
equal to 0.1µF.
The LM4954 is unity-gain stable and requires no external
components besides gain-setting resistors, an input coupling
capacitor, and proper supply bypassing in the typical appli-
cation. However, if a closed-loop differential gain of greater
than 10 is required, a feedback capacitor (C
needed as shown in Figure 2 to bandwidth limit the amplifier.
This feedback capacitor creates a low pass filter that elimi-
nates possible high frequency oscillations. Care should be
i
. A larger input coupling capacitor requires more charge to
B
equal to 2.2µF along with a small value of C
FIGURE 2. HIGHER GAIN AUDIO AMPLIFIER
(Continued)
F
) may be
DD
i
). This
(in the
B
11
AUDIO POWER AMPLIFIER DESIGN
A designer must first determine the minimum supply rail to
obtain the specified output power. By extrapolating from the
Output Power vs Supply Voltage graphs in the Typical Per-
formance Characteristics section, the supply rail can be
easily found.
At this time, the designer must make sure that the power
supply choice along with the output impedance does not
violate the conditions explained in the Power Dissipation
section.
Once the power dissipation equations have been addressed,
the required differential gain can be determined from Equa-
tion 2.
taken when calculating the -3dB frequency in that an incor-
rect combination of R
20kHz. A typical combination of feedback resistor and ca-
pacitor that will not produce audio band high frequency rolloff
is R
-3dB point of approximately 320 kHz. To calculate the value
of the capacitor for a given -3dB point, use Equation 3 below:
F
= 20kΩ and C
C
A
F
F
VD
= 25pf. These components result in a
= 1/(2πf
F
= (R
and C
f
/R
3dB
20129108
i
) 2
F
R
will cause rolloff before
F
) (F)
www.national.com
(2)
(3)