YDA137 Datasheet, PDF (7/20 Pages) YAMAHA CORPORATION – D- 2 STEREO 5W DIGITAL AUDIO POWER AMPLIFIER

YDA137
■Description of functions
●Digital Amplifier Function
YDA137
VPL
(VPR)
RI
INL
(INR)
RNP
RNP
VREFL
(VREFR)
Balanced
Pulse
Width
Modulation
Unit
(L-ch/R-ch)
First Operational
Amplifier Stage
Digital Amplifier
Stage
VDDPL
OUTPL
OUTPR)
VSSPL2
VDDPL
OUTML
OUTMR)
LO
CO
CO
RL
LO
VSSPL1
Amplifier function block diagram
Amplifier Section of YDA137 is composed of the first operational amplifier stage and the latter digital amplifier stage.
Gain of the first operational amplifier can be set by connecting input resistor (RI) and feedback resistor (RFB) externally.
In digital amplifier stage, digital amplifier output is feed-backed to the modulation circuit, and low distortion rate is
realized.
Digital amplifier output is connected to a speaker through the 2nd-order low-pass filter consisting of inductance (Lo) and
capacitance (Co). This eliminates carrier frequency content existing at the digital amplifier output, consequently only audio
signal is sent to a speaker.
Gain Setting
Gain of the first operational amplifier can be calculated by the following formula. Gain of aｎ internal digital amplifier is
8.0dB.
First operational amplifier stage
Digital amplifier stage
Gain
20×log(RFB/RI) dB (Using RI and RFB. Conditions：RI >2kΩ)
8.0dB
In the application circuit example, RI=33kΩ, RFB=39kΩ, total gain (Av) can be calculated by the following formula.
In this setting value, input sensitivity is 1Vrms, the maximum output could be obtained at 1Vrms input.
When input sensitivity is set to 150mVrms, it is set as RI=4.7kΩ and RFB=39kΩ.
Av(dB) = 20×log(39/33) + 8
= 9.5 (dB)
In gain setting of the first operational amplifier stage, it is necessary to obey the restriction that is described in the “Pop
Noise Rejection Function.” In addition, feed back resistor (RFB) needs to be 10kΩ or over because of the restriction on
operational amplifier drive capability.
7