ROHM BA5204F, BA5204 Datasheet

373

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 cou­pling capacitors are not required, and only one filter capacitor is needed which helps reduce set size. In addition to oper­ating 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.

Applications
3V compact cassette headphone stereos players, micro cassette players, and FM stereo radios

Features

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 .

6) Low distortion (0.05% at P

O = 5mW).

7) Good voltage gain balance between channels.

8) Good channel separation (60dB Typ.).

9) Input coupling capacitors not required.

10) Symmetrical pin assignments facilitates PCB de­sign.

Block diagram

374

Audio ICs BA5204F

Internal circuit configuration

Circuit description (refer to the Internal Circuit diagram)

(1) Preamplifier Stage
The preamplifier is comprised of the level-shift transistor
Q

101, a differential amplifier (Q102 and Q105), and the active

load (Q

103 and Q106). The input is a PNP transistor that

does not require a coupling capacitor.
(2) Pre-drive stage
Q

118 is the pre-drive transistor. Q122 and Q120 form the

load.
(3) Power stage
Comprised of phase-inverting transistor Q

120, and power

transistors Q

122 and Q123.

(4) Idling current setting circuit
The idling current is controlled so that the difference be­tween the V

BE of the power transistor Q122 and the VBE 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 VBE of Q121.

(5) Negative-feedback circuit
The closed-circuit gain with negative feedback is deter­mined by R

108, R102, 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 op­eration) to reduce the “pop” noise that occurs when pow­er is applied.

375

Audio ICs BA5204F

FAbsolute maximum ratings (Ta = 25_C)

FElectrical characteristics (Ta = 25_C, V

CC = 3V, f= 1kHz and RL = 32Ω)

FMeasurement circuit