FEDL2302DIGEST-05

OKI Semiconductor

ML2302

17/24

SPEAKER DRIVING AMPLIFIER

The ML2302 contains two OP amplifiers for driving a speaker; SPOUT– which is the inverting type output for a

voice multiplication signal SPIN and SPOUT+ which is the non-inverting type output.

Though SPOUT+ alone can be used, when differential outputs are used, it is possible to gain not only an amplitude

two times that of when a single OP amplifier is used but also a good volume even if a low power supply voltage is

used. The connection diagram of differential outputs are shown below.

Note 1: The gain of a speaker amplifier is determined by R1 and R2.

V (SPOUT–) = –

R2

R1

• V(SPIN)

V (SPOUT+) = –V(SPOUT–) =

R2

R1

• V(SPIN)

Note 2: C1 is an AC coupling capacitance. The cut-off frequency at a low field is determined by the following

equation.

Select a value of C1 in accordance with a pass band.

1

2

× π × C1 × R1

(Hz)

VR

R1

AOUT

SPIN

SPOUT–

SPOUT+

C1

R2

20 k

Ω

20 k

Ω