APA2121 datasheet(18/27 Pages) ANPEC

18 / 27 page

Rev. A.4 - Jul., 2013

APA2120/2121

www.anpec.com.tw

Volume Control Function

In Figure 2, input SE/BTL operates as below :

When the phonejack plug is inserted, the 1k

Ω resistor is

disconnected and the SE/BTL input is pulled high and

enables the SE mode. When the input goes to a high

level, the OUT- amplifier is shutdown which causes the

speaker to mute. Then, the OUT+ amplifier drives through

the output capacitor (C

C) into the headphone jack. W hen

there is no headphone plugged into the system, the con-

tact pin of the headphone jack is connected from the sig-

nal pin, and the voltage divider set up by resistors 100k

Ω

and 1k

Ω. Resistor 1kΩ then pulls low the SE/BTL pin,

enabling the BTL function.

APA2021 volume control curve

-44

-40

-36

-32

-28

-24

-20

-16

-12

-8

-4

0.2 0.4 0.6 0.8

1.2 1.4 1.6 1.8

2.2 2.4

2.6 2.8

3.2 3.4

3.6 3.8

(V)

Gain_BTL mode

Forward

Backward

Figure 3 : Gain setting vs VOLUME Pin Voltage.

Output SE/BTL Operation (Cont.)

Application Information (Cont.)

APA2120/1 have an internal stereo volume control that

setting is the function of the DC voltage applied to the

VOLUME input pin. The APA2120/1 volume control con-

sists of 32 steps that are individually selected by a vari-

able DC voltage level on the VOLUME control pin. The

range of the steps, controlled by the DC voltage, are from

20dB to -80dB. Each gain step corresponds to a specific

input voltage range as shown in table. To minimize the

effect of noise on the volume control pin, which can affect

the selected gain level, hysteresis and clock delay are

implemented. The amount of hysteresis corresponds to

half of the step width is shown in the volume control graph.

For the highest accuracy, the voltage is shown in the ‘rec-

ommended voltage’column of the table and used to se-

lect a desired gain. This recommended voltage is exactly

halfway between the two nearest transitions. The gain

levels are 2dB/step from 20dB to -40dB in BTL mode,

and the last step at -80dB as mute mode.

Input Resistance, Ri

The gain for each audio input of the APA2120/1 is set by

the internal resistors (Ri and Rf) of volume control ampli-

fier in inverting configuration.

SE Gain =

(2)

AV = -

(3)

BTL Gain = -2 x

BTL mode operation brings the factor of 2 in the gain

equation due to the inverting amplifier mirroring the volt-

age swing across the load. For the varying gain setting,

APA2120/1 generate each input resistance on the figure

4. The input resistance will affect the low frequency per-

formance of audio signal. The minmum input resistance

is 10k

Ω when gain setting is 20dB, and the resistance

will ramp up when close loop gain below 20dB. The input

resistance has wide variation (+/-10%) caused by the pro-

cess variation.

Figure 4: Input Resistance vs Gain Setting.

Ri vs Gain(BTL)

100

120

-40

-30

-20

-10

Gain(dB)

Ri(k

Ω)

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