LM4753 National Semiconductor, LM4753 Datasheet - Page 7

• Manufacturer Part Number: LM4753
• Description: Dual 10W Audio Power Amplifier w/Mute/ Standby and Volume Control
• Manufacturer: National Semiconductor

Application Information
abled, it overrides the mute function and places the IC in its
power conserving mode. If the mute function is enabled
while in standby mode, the IC will continue to remain in
standby mode. After the standby function is disabled, the IC
will be placed into mute mode. Please refer to the Table 1 for
each input condition.
To prevent mechanical switch bouncing from adversely af-
fecting the functionality of an IC, an RC lowpass filter should
be used as shown in Figure 2 . This circuit replaces the need
for a debounce circuit when using a mechanical switch to
control the IC logic functions. However, most systems typi-
cally utilize a microprocessor or COP microcontroller to inter-
face with the logic control functions of the LM4753. When a
clean logic signal is used, as from a microcontroller, the RC
lowpass filter is not required.
DC Volume Control
The DC volume control for the LM4753 works between 0V
and 5V. When the volume pin (pin 3) is 0V, the IC’s preamp
stage is fully attenuated to 80 dB. When the volume pin is at
5V, the preamp stage passes audio at 0 dB.
The DC volume attenuation curve for the LM4753 is in-
tended to provide smooth accurate attenuation changes at
higher DC voltages, but then attenuate fast to 80 dB at lower
DC voltages. This means that when the volume control is
turned down, the amplification is quickly attenuated, while at
normal listening levels, attenuation changes are more
gradual. Please refer to the Volume Attenuation vs DC Volt-
age curve in the Typical Performance Characteristics sec-
tion.
The DC voltage to pin 3 can be controlled with a potentiom-
eter as shown in Figures 1, 3 . A 100 k
capacitor form an RC lowpass filter that keeps any unneces-
sary noise from coupling into the device. Any noise that is
coupled into the device is gained up by 40 dB.
0V or open
0V or open
5V
5V
TABLE 1. Mute and Standby Functional Conditions
Standby
(Pin 9)
0V
5V or open
0V
5V or open
(Pin 10)
Mute
resistor and a 1 µF
(Continued)
Music Plays
Mute Mode
Standby Mode
Standby Mode
Conditions
Operating
7
Turn On/Off Characteristics
In order to minimize turn on and off pops, the LM4753 should
be powered up by using the sequence described below.
Figure 4 shows the sequence for turn on and off.
Since the power supply voltage of the power amplifier is
about 4 times more than a 5V power supply, it is assumed
that the logic voltage supply for the standby and mute func-
tions is up before the large power supply reservoir capacitors
are charged. The LM4753 should be placed into standby
mode before the undervoltage protection circuitry is dis-
abled. The undervoltage protection circuitry will keep the out-
puts of the LM4753 at 0V until the voltage from V
is about 9.5V. If the standby function is disabled when the
supply voltage exceeds this value, the single-supply biasing
of the output stage will then begin to charge up to V
pop performance under this condition is quite good, how-
ever, it is highly recommended that the Mute and Standby
pin voltages are high at 5V while the main power supply volt-
age, V
Once the main supply voltage is up to its full value, the
standby function can then be brought low to 0V. The biasing
of the amplifier and the output stage will then begin to charge
up to V
mately 7 mA until the standby function is disabled, at which
point, the supply current increases to approximately 13 mA
while in mute mode.
Once the single-supply biasing is established, the mute pin
voltage can be brought down to 0V, allowing the IC to amplify
the input signal. As shown in Figure 4 , the input signal that is
applied to the IC all throughout the power-up process is not
passed to the speaker until the mute function is disabled.
The typical quiescent power supply current while in play
mode is approximately 80 mA.
The same sequence should be applied when powering down
the device. First the IC should be placed into mute mode,
muting the output, then placed into standby mode where the
bias and output coupling caps are gradually discharged to
ground. Once the biasing of the IC is brought to ground, the
main power supplies can be powered down. This power-up
and power-down sequence is highly recommended. Abrupt
changes in output current from enabling standby while the
output is driving an inductive load (like a speaker) may cause
the IC to handle extreme levels of power due to inductive
kickback. The IC may not be able to handle this and should
be avoided.
CC
CC
, is ramping up.
FIGURE 3. Volume Pin Lowpass Filter
/2. Notice that the supply current draw is approxi-
DS100043-27
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CC
CC
to GND
/2. The