AA4003 Datasheet, PDF (12/18 Pages) BCD Semiconductor Manufacturing Limited – 2W STEREO AUDIO POWER AMPLIFIER WITH SHUTDOWN

Data Sheet
2W STEREO AUDIO POWER AMPLIFIER WITH SHUTDOWN
AA4003
Application Information (Continued)
f_CIL
=
1
2πR_I ∗ C_I
.............................................(1)
Similarly, for output stage in SE mode, output
capacitor (C_OUT), and headphone load also form a first
order High Pass Filters, and its cut-off frequency is
determined by equation 2.
f_COL
=
1
2πR_HP ∗ C_OUT
......................................(2)
Example:
V_DD=5V, R_L=8Ω, BTL configuration, Desired output
power P_O=1.0W (each channel), THD+N ≤ 1%.
Input signal, V_IN=1.0VRMS from D-A converter.
Step 1,
To check if the chip can deliver 1W to 8Ω load with the
limitation of THD+N ≤ 1%, V_DD=5V. From Figure 6,
Figure 12, AA4003 can deliver 1W to 8Ω load each
channel.
Step 2,
If yes, to calculate output voltage,
The purpose of bypass capacitor (Cb) is to filter
internal noise, reduce harmonic distortion, and
improve power supply rejection ratio performance.
Tantalum or ceramic capacitor with low ESR is
recommended, and it should be placed as close as
possible to the chip in PCB layout. The chip will not
work until internal DC bias is set up completely. So the
size of Cb will also affect the chip start up time, which
is approx linearly proportional to the value of bypass
capacitor. For AA4003, here are various start-up times
for several typical capacitor values. (see Figure 17)
Cb (μF)
0.33
0.47
1.0
Start up Time (ms)
340
420
970
For AA4003 power supply, it is better to use an
individual power source generated from voltage
regulator split from video, digital circuit units in
system. The power supply bypass capacitors, C_S, is
recommended to use one low ESR electrolytic
capacitor between 4.7μF to 10μF with a parallel 0.1μF
ceramic capacitor which is located close to the chip.
Setup Proper Gain, Design Example
The closed loop gain of AA4003 is determined by the
ratio of feedback resistor (R_F) to input resistor (R_I).
A_V
=
R_F
R_I
........................................................(3)
Oct. 2007 Rev. 1. 1
V_OUT = P_O ∗R_L = 1*8 = 2.83V_RMS
So pass-band gain, AV=V_OUT/V_IN=2.83x.
Step 3,
Assuming input resistor is 20kΩ, the feedback
resistor=20kΩ*1.415=28.3kΩ.. Select the closest
standard value 28kΩ.
Shutdown
AA4003 has a shutdown feature to reduce power
consumption. If apply high level to shutdown pin,
output amplifiers will be turned off, bias circuit is also
disabled, the maximum current drawn from V_DD is less
than 2.0μA. A logic low level will enable the device.
Optimizing CLICK/POP Noise
The AA4003 includes optimized circuits to suppress
CLICK/POP noise during power up/power down
transition.
In BTL mode the AA4003 can effectively reduce most
common mode signal including CLICK/POP noise.
In SE mode, optimized ramp for rise/fall edge of BIAS
can significantly reduce click/pop noise due to charge
and/or discharge output capacitor (C_OUT).
Furthermore, increasing bypass capacitor value (Cb)
can slower ramp of charging bypass capacitor, prolong
start-up time, mask most of transient noises before bias
voltage is set up completely. It is recommended to use
1.0μF capacitor with lower ESR.
BCD Semiconductor Manufacturing Limited
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