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.

TABLE 1. Mute and Standby Functional Conditions

Standby

(Pin 9)

Mute

(Pin 10)

Operating

Conditions

0V or open

0V

Music Plays

0V or open

5V or open

Mute Mode

5V

0V

Standby Mode

5V

5V or open

Standby Mode

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

Ω resistor anda1µF

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.

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.

DS100043-27

FIGURE 3. Volume Pin Lowpass Filter

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