Audio ICs
3V / 35mW dual power amplifier
BA5204F
The BA5204F is a dual-channel power amplifier designed for 3V stereo headphone tape players. There is almost no
“pop” sound generated when the power is switched on and off, so this IC is ideal for headphone applications. Input cou-
pling capacitors are not required, and only one filter capacitor is needed which helps reduce set size. In addition to oper-
ating off low voltage, the IC has low distortion, making it suitable for Hi-Fi applications. The circuit can operate down to
1.5V, and has excellent ripple rejection ratio, so it is not adversely influenced by the motor or tape transport systems.
FApplications
3V compact cassette headphone stereos players, micro cassette players, and FM stereo radios
FFeatures
1) Rated output of 35mW (RL = 32Ω) off a 3V power
supply.
2) Low “pop” noise when power is switched on and off.
3) Low quiescent current (13mA).
4) Excellent ripple rejection ratio (38dB).
5) Begins operating at 1.5V.
FBlock
diagram
6)
7)
8)
9)
10)
Low distortion (0.05% at P
O
= 5mW).
Good voltage gain balance between channels.
Good channel separation (60dB Typ.).
Input coupling capacitors not required.
Symmetrical pin assignments facilitates PCB de-
sign.
373
Audio ICs
FInternal
circuit configuration
BA5204F
FCircuit
description (refer to the Internal Circuit diagram)
(1) Preamplifier Stage
The preamplifier is comprised of the level-shift transistor
Q
101
, a differential amplifier (Q
102
and Q
105
), and the active
load (Q
103
and Q
106
). The input is a PNP transistor that
does not require a coupling capacitor.
(2) Pre-drive stage
Q
118
is the pre-drive transistor. Q
122
and Q
120
form the
load.
(3) Power stage
Comprised of phase-inverting transistor Q
120
, and power
transistors Q
122
and Q
123
.
(4) Idling current setting circuit
The idling current is controlled so that the difference be-
tween the V
BE
of the power transistor Q
122
and the V
BE
of
the phase-inverting transistor Q
120
is the same as the dif-
ference between the V
F
of the constant-voltage diode
Q
117
and the V
BE
of Q
121
.
(5) Negative-feedback circuit
The closed-circuit gain with negative feedback is deter-
mined by R
108
, R
102
, and the value of the resistor con-
nected to the NFB pin. Part of the gain setting resistance
is on the chip (R
102
) to reduce variance between compo-
nents.
(6) “Pop” noise elimination circuit
The IC has an internal timing circuit (with switch for op-
eration) to reduce the “pop” noise that occurs when pow-
er is applied.
374
Audio ICs
FAbsolute
maximum ratings (Ta = 25_C)
BA5204F
FElectrical
characteristics (Ta = 25_C, V
CC
= 3V, f= 1kHz and R
L
= 32Ω)
FMeasurement
circuit
375
Audio ICs
FApplication
example
BA5204F
FAttached
components (Fig. 15)
C
1
: filter capacitor
The recommended value is 330µF. If this is reduced too
much, the ripple rejection ratio will drop. This capacitor
also sets the muting time when power is applied. Reduce
the value of this capacitor if you wish to shorten the start-
up time. On the other hand, if you wish to reduce the
“pop” noise further, increase the value of this capacitor to
lengthen the startup time.
C
2
and C
3
: bootstrap capacitors
The recommended value is 47µF. If the capacitance is
too small, the IC will not be able to produce its rated pow-
er in the bass region and distortion will increase.
C
5
and C
6
: feedback circuit DC blocking capacitors
These capacitors and RNF set the bass cutoff frequency.
ch
1
G G G G
f
LC1
=
ch
2
G G G G
f
LC2
=
1
2π
S
C
5
S
(R
NF1
)R
102
)
1
2π
S
C
6
S
(R
NF2
)R
202
)
R
NF1
and R
NF2
determine the amount of feedback for the
feedback circuit. These resistors determine the closed-
circuit voltage gain (G
VC
).
C
7
and C
8
: depending on the PCB design, and output cir-
cuit wiring, feedback may be applied to the IC’s internal
circuits and cause high-frequency oscillation. These ca-
pacitors prevent this from happening. They also increase
the amount of design freedom with regard to the output
wiring and PCB artwork. Design the PCB so that the
length of the wiring from ch1 and ch2 to capacitors and
from the capacitors to GND is as short as possible. Mylar
capacitors of about 0.01µF are appropriate for this ap-
plication, although active capacitors may also be used.
The residual impedance and resonant frequency will dif-
fer depending on the type of capacitor and therefore have
some influence on the effectiveness.
C
9
and C
10
: output coupling capacitors
The recommended value is 220µF. If the capacitance is
too small, the IC will not be able to produce its rated pow-
er in the treble region and distortion will increase.
376
Audio ICs
FElectrical
characteristics curves
BA5204F
377
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