LC823450 datasheet(97/112 Pages) ONSEMI

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LC823450

www.onsemi.com

Class−D AMP

Figure 46. Class−D AMP

Ipp(Irms)

Headphone L−ch

LOUT

This LSI

Mut e

Nch Power

FET

ROUT

Power

Mut e

Ipp(Irms)

Headphone R−ch

0.22

μF

10 k

220

μF

220

μΗ

∼ 10 Ω

0.22

μF

220

μF

220

μΗ

∼ 10 Ω

10 k

220

μF or

0.1

μF

AVSSDAMPR

AVDDDAMPR

AVSSDAMPL

AVDDDAMPL

87. Add the bypass condenser (0.1

μF) between AVDDDAMPL and AVSSDAMPL, AVDDDAMPR and AVSSDAMPR as

close as possible to terminals

88. Add the large electrolyte capacitor (220

μF or more recommended) to AVDDDAMPL, AVDDDAMPR terminal to reject

the noise and reduce the pumping phenomenon of Class−D AMP.

89. Check the voltage level of AVDDDAMPL, AVDDDAMPR and make sure not to exceed 1.65 V (recommended operating

voltage) by using playback of 20 Hz, 0db (full scale) sin wave

90. Add the bypass condenser (0.1

μF) between AVDDDAMPL and AVSSDAMPL, AVDDDAMPR and AVSSDAMPR as

close as possible to terminals

91. Add the large electrolyte capacitor (220

μF or more recommended) to AVDDDAMPL, AVDDDAMPR terminal to reject

the noise and reduce the pumping phenomenon of Class−D AMP.

92. Check the voltage level of AVDDDAMPL, AVDDDAMPR and make sure not to exceed 1.65 V (recommended operating

voltage) by using playback of 20 Hz, 0db (full scale) sin wave

Output power calculation

[ condition ]

• The DC resistance element of the coil, capacitor is

small

• Maximum output amplitude = 90% (Theoretical Value

of Delta−sigma Circuit) to power supply of PWM

• Class−D AMP power supply (AvDDDAMPL,

AVDDDAMPR) = 1.2 V

• Class−D AMP Turning on resistance of internal

transistor(Ron) = 2

• Headphone load resistance(RL) = 15 Ω

• Series resistance(Rd) = 0 Ω

Assume the current that flows to the headphone to be Ipp:

Ipp = (1200 / 2)

× 0.9 / (15 + 2) = 31.7 (mA)

Irms = Ipp / SQRT(2) = 22.4 (mA)

Prms = Irms ^ 2

× 15 = 7.53 (mW)

Power Supply

Class−D AMP

power

supply

(AVDDDAMPL,

AVDDDAMPR) must use a transient response and good

power supply. When the power supply where the transient

response is bad is used and the capacity of the capacitor is

small, a peculiar pumping phenomenon to Class−D AMP is

generated. The power supply voltage must not exceed the

recommended

operating

range

when

the

pumping

phenomenon occurs.

Class−D AMP output is PWM. The power supply noise

affects the output of Class−D AMP.

Power sources which have large internal impedance such

as dry cell should not be directly connected to power supply

of Class−D AMP, and those which have large switching

noise such as switching regulator are not suitable and need

to be taken care of.

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