AA4002 Datasheet, PDF (13/22 Pages) BCD Semiconductor Manufacturing Limited – STEREO 2W AUDIO POWER AMPLIFIER

Data Sheet
STEREO 2W AUDIO POWER AMPLIFIER
AA4002
Application Information
SE/BTL Mode, HP_SENSE Pin
The AA4002 can be operated in 2 types of output
configurations, SE (Single-Ended) mode and BTL
(Bridged-Tied-Load) mode, determined by
HP_SENSE pin (pin 21) logic level. (Here is the
discussion about left channel only, it also applies to
right channel.)
28, R_PU=100k, R_L=1.5k, DC voltage at HP_SENSE is
about 75mV. AC signal equals output amplitude of
OUT- through C_OUT, so signal at HP_SENSE node is
75mV DC plus AC signal. The maximum Peak-to-
Peak voltage at OUT- is not greater than V_DD=5.0V
supply voltage, so the positive maximum voltage of
HP_SENSE node is not greater than
2.5V+75mV=2.575V, which can not reach HP_SENSE
input high level minimum value (4.0V), there is no risk
of mode switching between SE and BTL.
10kΩ
Bias
10kΩ
_
+
20kΩ
OP1
Left Out- 17
20kΩ
_
+ Left Out+ 15
OP2
C_OUT
220µF
+
R_L
1.5kΩ
Figure 22. BTL Configuration in Left Channel
If applying high level to pin 21, the output of OP2 unit
is in high impedance, the chip operates in SE mode.
There is no current loop between OUT+ and OUT-,
also no power consumption.
When HP_SENSE pin is held low, OP2 unit is turned
on, the chip operates in BTL mode. AC signal at OUT+
is -180^o phase shift of OUT-. OP2 has fixed unity gain
internally, so DC components (Bias voltage, approx
1/2 V_DD) between OUT+, OUT- is canceled. There is
no need for DC block capacitors in system.
In BTL mode, voltage between speaker load is about 2
times that in SE mode, so there is 4 times output power
compared to SE mode with same load.
In SE mode, output audio signal rides on Bias voltage
at OUT-, so it is necessary to use capacitor to block
DC bias and couple AC signal. See Figure 28 typical
application circuit.
It is recommended to connect HP_SENSE to the
control pin of headphone jack, illustrated in Figure 28.
When headphone plug is not inserted, the voltage of
HP_SENSE pin is determined by voltage divider
formed by R_PU, R_L. For given resistors value in Figure
Sep. 2006 Rev. 1. 1
HP_SENSE pin can also be connected to MCU I/O
port, it is necessary to note that AA4002 still can drive
headphone even in BTL mode because OUT- is always
active whatever SE or BTL mode.
Internal/External Gain, Gain SELECT Pin
The AA4002 provides 2 selectable feedback loops,
Internal and External determined by SELECT pin (pin
3) logic level. Applying low level to SELECT pin, the
AA4002 switches to internal feedback loop, OP1
works as unity gain. If applying high level to SELECT
pin, external components are used as feedback loop,
and the gain is expressed by formula below.
A_VFB
=
( R_BS
//
ZC_BS ) +
R_I
R_F
..............................(1)
Here ZC_BS is the impedance of bass boost capacitor,
ZC_BS=1/2π*f*C_BS. So A_VFB approaches 2 points,
A_VFBLF at low frequency, A_VFBHF at high frequency,
expressed by formula 2 and 3.
A_VDLF
=
R_BS + R_F
R_I
.............................................(2)
A_VFBHF
=
R_F
R_I
........................................................(3)
Bass Boost
From above discussion, the AA4002 can improve gain
of audio signal at low frequency, which is hard to
listening for human ears relative to middle band (2kHz
to 3kHz). The boost corner frequency is determined by
formula 4.
BCD Semiconductor Manufacturing Limited
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