YDA137 Datasheet, PDF (8/20 Pages) YAMAHA CORPORATION – D- 2 STEREO 5W DIGITAL AUDIO POWER AMPLIFIER

YDA137
The following “low-frequency boost filter circuit “ can be configured by using the first operational amplifier stage.
This filter has frequency characteristics as shown in the following “low-frequency boost filter characteristics”, and boost
gain (Ab), turn-over frequency (fb), and turn-over frequency gain (At) to the first operational amplifier gain(Av) are found
by the following formulas.
Ab(dB) = 20×log((R_FB+R_B)/R_FB)
fb(Hz) = 1/2×π×R_B×C_B
At(dB) = 20×log(1+R_B/(2^1/2×R_FB))
In the application circuit example, high-cut capacitance (CFB) is added for input signal band restriction. The value can be
adjusted as necessary. (cut-off frequency is 1/(2×π×CFB×RFB)） In addition, DC-cut capacitance (CI) is added for
input DC current limitation. This capacitance and input resistance (RI) make a low-cut filter. Set a cut-off frequency low
enough （Cut-off frequency is 1/(2×π×CI×RI)）.
Selection of Coil for an output filter
Cut-off frequency (fc) of LC low-pass filter that is connected to the digital amplifier output can be found by the following
formula.
In addition, to obtain the ideal frequency characteristics, select 0.7 or so for Q value of LCR resonance circuit.
Fc (Hz) = 1/(2×π×√(Lo×Co))
Q = (RL/2)×√(Co/Lo) =0.7
Generally, cut-off frequency is selected to 50kHz, and the following values are used according to the speaker impedance.
RL（load impedance）
Lo（inductance）
Co（capacitance）
2Ω
4.7μH
2.2μF
3Ω
6.8μH
1.5μF
4Ω
10μH
1μF
Distortion rate or sound quality may change depending upon the type of coil to use. In addition, select appropriate coils
according to the necessary characteristics.
Measure against ringing of output terminal
When ringing with big peak voltage has occurred for the output terminal, IC may incorrect-operate, or IC may be damaged.
Perform the measure against ringing by adding capacitor between a VDDPL and VSSPL1 terminals, between VDDPL and
VSSPL2 terminals, between VDDPR and VSSPR1 terminals, between VDDPR and VSSPR2 terminal. A ceramic capacitor
(4.7μF) with the sufficient frequency characteristic should be used for the adding capacitor, and if possible, it should set
near the terminal.
Even if it performs the above measure, when ringing occurs, add a resistor (Rrng) and a capacitor (Crng) to an output
terminal like the application circuit example. As a standard of the measure against ringing, adjust a constant so that a peak
voltage value becomes less than 9V.
8