YDA137

11

●

Headphone Amplifier Function

Analog

Input

INL/R

Rsw=

400Ω

19.6kΩ

30kΩ

30kΩ

VREFL/R

VREFL/R

HPOL/R

ENB

Headphone Amplifier Circuit

When setting H to HP terminal, it enters headphone amplifier output mode. At this time, the digital amplifier enters the

Mute Mode.

Headphone amplifier section is comprised of the first stage operational amplifier and a class AB single-end output

amplifier.

The latter stage is a high current output amplifier applicable to 16Ω load. VREF terminal voltage (vias) is applied to the

headphone amplifier output, so that connect the output to headphone through AC coupling capacitor, as shown in the

application circuit example.

Gain Setting

Gain of the first inverting amplifier can be calculated according to the following formula. In addition, class AB amplifier

gain is 0dB.

4.7kΩis selected as an input resistor RI, and total gain is set to 11.7dB.

In this setting, 150mVrms input can yield the maximum output of 20mW.

Relation between an external resistor value and output level in typical input sensitivity is shown in the table below.

Input Sensitivity

150mVrms

1.0Vrms

2.0Vrms

4.7kΩ

33kΩ

68kΩ

for digital amplifier

39kΩ

39kΩ

43kΩ

3.14Vrms (3.28W or so)

2.98Vrms (2.96W or so)

3.19Vrms (3.38W or so)

0.566Vrms (20.0mW)

0.586Vrms (21.4mW)

0.573Vrms (20.5mW)

of the headphone amplifier.

f

：R

Headphone Amplifier Switching Function

By making up a headphone circuit as shown in the application circuit example, two modes can be switched automatically

according to the existence of headphone.