|YDA137||STEREO 5W DIGITAL AUDIO POWER AMPLIFIER|
|YDA137 Datasheet PDF : 20 Pages |
●Headphone Amplifier Function
Headphone Amplifier Circuit
When setting H to HP terminal, it enters headphone amplifier output mode. At this time, the digital amplifier enters the
Headphone amplifier section is comprised of the first stage operational amplifier and a class AB single-end output
In the first stage operational amplifier section, gain can be set by connecting an input resistor RI externally.
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 of the first inverting amplifier can be calculated according to the following formula. In addition, class AB amplifier
gain is 0dB.
AVHP = 20×log10(19.6k / (RI + 400))
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.
External input resistor RI
External feedback resistor RFB
for digital amplifier
Digital amplifier output (RL=3Ω)
Headphone amplifier output (RL=16Ω)
3.14Vrms (3.28W or so)
2.98Vrms (2.96W or so)
3.19Vrms (3.38W or so)
A low cutoff frequency is found by the following formula with an AC coupling capacitor (CHO) and a load resistor (RHO)
of the headphone amplifier.
fCHP = 1 ／ (2×π×CHO×RHO) ：RHO＝load resistor
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.
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