AA4002 Datasheet, PDF (15/22 Pages) BCD Semiconductor Manufacturing Limited – STEREO 2W AUDIO POWER AMPLIFIER

Data Sheet
STEREO 2W AUDIO POWER AMPLIFIER
AA4002
Application Information (Continued)
But, decreasing voltage from 3.562V (point F), gain
does not change immediately, the change occurs at
3.5V (point E). There is a hysteresis which guarantees
that the volume control is monotonic, with immunity
against noise coupled from system. In above Table 1,
the column of Low Level means the lower threshold
voltage with the voltage of DC VOL varying from high
to low, High Level column means the other upper
threshold voltage DC VOL voltage varying from low
to high.
Mute, Shutdown
When applying high level to MUTE pin (pin 5), the
AA4002 will mute output stage stereo dock output-
whatever in BTL or SE mode. The AA4002 offers
shutdown function which can further reduce power
consumption. SHUTDOWN pin (pin 2) should be held
low in normal operation. If applying high level to
SHUTDOWN pin, the AA4002 will turn off internal
bias circuits, enter into shutdown mode with very low
quiescent current, 0.7µA Typ. MUTE, SHUTDOWN
pin should be tied to high or low level to avoid undes-
ired operation state.
fixed gain, ignoring MUTE and HP_SENSE pin logic
level. For AA4002, V_DETECT is about 2.8V. Beep sig-
nal passes through Left/Right channel input path, the
gain under BTL load is only dependent on the ratio of
R_F(L/R) to R_BEEP.
A_{VBEEP(L / R)}
=
2∗
R_{F (L / R)}
R_BEEP
.................................(6)
For resistors value given in Figure 28, A_VBEEP is about
0.2 (-14dB). If this feature is not used, connecting the
capacitor (C_BEEP) to ground, it is recommended
removing two resistors (R_BEEP, 200kΩ), to minimize
crosstalk between left and right channel.
C_I, C_OUT, C_B and C_S (Power Supply
Bypassing Capacitor) Selection
For input stages of Left/Right channel, input capacitors
(C_IL, C_IR), are used to accommodate different DC level
between input source and AA4002 bias voltage (about
1/2 VDD). Input capacitors (C_IL, C_IR) and input
resistors (R_IL, R_IR) form first order High Pass Filters,
which determine the corner frequency,
Left/Right Dock Output
There are stereo amplifiers built-in AA4002 front-end
input stages. It provide very low distortion audio moni-
tor signal for line out, the pass-band gain is determined
by external feedback resistors,
A = ^RR _{VDOCK (L / R)}
F (L / R)
I (L / R)
.....................................(5)
The dock output is also used as input source for back-
end amplifiers, so the gain of docking output
(A_VDOCK) will affect total loop gain. The function of
C_OUT(L/R) (0.1µF) serial in Left/Right dock output is to
remove DC bias.
Beep Detect
Beep feature is used in Notebook PC system for alert-
ing. If peak-to-peak voltage of beep signal applied to
BEEP DETECT pin (pin 11) exceeds a certain voltage
called detect voltage, the feature will be activated, then
AA4002 will be forced at BTL mode with internal
Sep. 2006 Rev. 1. 1
f_{CI (L / R)}
=
1
2πR_{I (L / R)} ∗ C_{I (L / R)}
..........................(7)
For given values in Figure 28, R_IL=R_IR=20kΩ,
C_IL=C_IR=0.33µF, the corner frequency of input stage is
about 24Hz.
Similarly, for output stage in SE mode, output
capacitor (C_OUT), and headphone load also form a first
order High Pass Filter, and its cut-off frequency is
determined by classic formula below.
π ^{fCO(L / R) =} 2
1
R ∗ C _{HP(L / R) O(L / R)}
....................(8)
For bypass capacitor (C_B), the purpose is to filter
internal bias noise, reduce harmonic distortion, and
improve power supply rejection ratio performance.
Tantalum or ceramic capacitor with low ESR is
recommended, and is placed as close as possible to
chip bypass pin in PCB layout. Both input and output
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