LM4952TSBD National Semiconductor, LM4952TSBD Datasheet - Page 15

• Manufacturer Part Number: LM4952TSBD
• Description: BOARD EVALUATION LM4952TS
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM4952TSBD

• Amplifier Type: Class AB
• Output Type: 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 3.8W x 2 @ 4 Ohm
• Voltage - Supply: 9.6 V ~ 16 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4952
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Information
seen by the DC Vol input. Though attenuated by the voltage
divider action of the potentiometer and the series resistor,
these fluctuations may cause perturbations in the perceived
volume. An easy and simple solution that suppresses these
perturbations is a 10µF capacitor connected between the DC
Vol pin and ground. See the result of this capacitor in Figure
8. This capacitance can also be supplemented with bulk
capacitance in the range of 1000µF to 10,000µF connected
to the unregulated power supply’s output. Figure 10 shows
how this bulk capacitance minimizes fluctuations on V
If space constraints preclude the use of a 10µF capacitor
connected to the DC Vol pin or large amounts of bulk supply
capacitance, or if more resistance to the fluctuations is de-
sired, using an LM4040-4.1 voltage reference shown in Fig-
ure 9 is recommended. The value of the 91kΩ resistor,
already present in the typical volume applications circuit,
should be changed to 62kΩ. This sets the LM4040-4.1’s bias
current at 125µA when using a nominal 12V supply, well
within the range of current needed by this reference.
connected between the DC VOL pin and GND (Trace D)
DC volume control voltage and attenuate power supply
variations when using unregulated supplies that would
FIGURE 8. Same conditions and waveforms as shown
FIGURE 9. Using an LM4040–4.1 to set the maximum
in Figure 7, except that a 10µF capacitor has been
otherwise perturb the volume setting.
(Continued)
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DD
.
15
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Two quantities determine the value of the input coupling
capacitor: the lowest audio frequency that requires amplifi-
cation and desired output transient suppression.
The amplifier’s input resistance and the input capacitor (C
produce a high pass filter cutoff frequency that is found using
Equation (5).
As an example when using a speaker with a low frequency
limit of 50Hz and based on the LM4952’s 44kΩ nominal
minimum input resistance, C
0.072µF. The 0.39µF C
LM4952 to drive high efficiency, full range speaker whose
response extends below 30Hz.
Similarly, the output coupling capacitor and the load imped-
ance also form a high pass filter. The cutoff frequency
formed by these two components is found using Equation (6)
Expanding on the example above and assuming a nominal
speaker impedance of 4Ω, response below 30Hz is assured
if the output coupling capacitors have a value, using Equa-
tion (6), greater than 1330µF.
Bypass Capacitor Value
Besides minimizing the input capacitor size, careful consid-
eration should be paid to value of C
connected to the BYPASS pin. Since C
how fast the LM4952 settles to quiescent operation, its value
is critical when minimizing turn-on pops. The slower the
LM4952’s outputs ramp to their quiescent DC voltage (nomi-
nally V
equal to 4.7µF along with a small value of C
of 0.1µF to 0.39µF) produces a click-less and pop-less shut-
down function. As discussed above, choosing C
than necessary for the desired bandwidth helps minimize
clicks and pops.
Routing Input and BYPASS Capacitor Grounds
Optimizing the LM4952’s low distortion performance is easily
accomplished by connecting the input signal’s ground refer-
ence directly to the TO263’s grounded tab connection. In like
FIGURE 10. Same conditions and waveforms as shown
in Figure 8, except that a 4700µF capacitor has been
connected between the V
DD
/2), the smaller the turn-on pop. Choosing C
f
COUT
F
CIN
= 1/(2πR
INA
= 1/(2πR
shown in Figure 2 allows the
DD
IN
pin and GND (Trace A)
LOAD
, using Equation (5) is
IN
C
C
BYPASS
IN
OUT
)
BYPASS
)
IN
, the capacitor
(in the range
IN
www.national.com
determines
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no larger
BYPASS
(5)
(6)
IN
)