參數(shù)資料
型號(hào): NCP2820
廠商: ON SEMICONDUCTOR
英文描述: 2.65W Filterless Class-D Audio Power Amplifier(2.65W單通道音頻放大器)
中文描述: 2.65W無濾波器D類音頻功率放大器(2.65W單通道音頻放大器)
文件頁數(shù): 13/20頁
文件大?。?/td> 222K
代理商: NCP2820
NCP2820
http://onsemi.com
13
APPLICATION INFORMATION
NCP2820 PWM Modulation Scheme
The NCP2820 uses a PWM modulation scheme with each
output switching from 0 to the supply voltage. If V
in
= 0 V
outputs OUTM and OUTP are in phase and no current is
flowing through the differential load. When a positive signal
is applied, OUTP duty cycle is greater than 50% and OUTM
is less than 50%. With this configuration, the current through
the load is 0 A most of the switching period and thus power
losses in the load are lowered.
Figure 37. Output Voltage and Current Waveforms into an Inductive Loudspeaker
DC Output Positive Voltage Configuration
OUTP
OUTM
Load Current
+Vp
0 V
Vp
0 A
Voltage Gain
The first stage is an analog amplifier. The second stage is
a comparator: the output of the first stage is compared with
a periodic ramp signal. The output comparator gives a pulse
width modulation signal (PWM). The third and last stage is
the direct conversion of the PWM signal with MOS
transistors Hbridge into a powerful output signal with low
impedance capability.
The total gain of the device is typically set to:
300 k
Ri
Input Capacitor Selection (C
in
)
The input coupling capacitor blocks the DC voltage at the
amplifier input terminal. This capacitor creates a highpass
filter with R
in
, the cutoff frequency is given by
Fc
2
Ri
When using an input resistor set to 150 k , the gain
configuration is 2 V/V. In such a case, the input capacitor
selection can be from 10 nF to 1
F with cutoff frequency
values between 1 Hz and 100 Hz. The NCP2820 also
includes a built in low pass filtering function. It’s cut off
frequency is set to 20 kHz.
1
Ci
.
Optional Output Filter
This filter is optional due to the capability of the speaker
to filter by itself the high frequency signal. Nevertheless, the
high frequency is not audible and filtered by the human ear.
An optional filter can be used for filtering high frequency
signal before the speaker. In this case, the circuit consists of
two inductors (15
H) and two capacitors (2.2
(Figure 38). The size of the inductors is linked to the output
power requested by the application. A simplified version of
this filter requires a 1 F capacitor in parallel with the load,
instead of two 2.2 F connected to ground (Figure 39).
Cellular phones and portable electronic devices are great
applications for Filterless ClassD as the track length
between the amplifier and the speaker is short, thus, there is
usually no need for an EMI filter. However, to lower radiated
emissions as much as possible when used in filterless mode,
a ferrite filter can often be used. Select a ferrite bead with the
high impedance around 100 MHz and a very low DCR value
in the audio frequency range is the best choice. The
MPZ1608S221A1 from TDK is a good choice. The package
size is 0603.
F)
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