LS1240A

July 1998

ELECTRONIC TWO - TONE RINGER

®

.

LOW CURRENT CONSUMPTION, IN ORDER

TO ALLOW THE PARALLEL OPERATION OF 4

DEVICES

.

INTEGRATED

RECTIFIER

BRIDGE

WITH

ZENER DIODES TO PROTECT AGAINST

OVERVOLTAGES

.

LITTLE EXTERNAL CIRCUITRY

.

TONE AND SWITCHING FREQUENCIES AD-

JUSTABLE BY EXTERNAL COMPONENTS

.

INTEGRATED VOLTAGE

AND CURRENT

HYSTERESIS

DESCRIPTION

LS1240A is a monolithic integrated circuit designed

to replace the mechanical bell in telephone sets in

connection with an electro-acoustical converter. It

can drive directly a piezoceramic converter (buzz-

er)or a dynamic loudspeaker.

The output current capability of LS1240A is higher

than standard ringer. For driving a dynamic loud-

speaker LS1240A can simply use a decoupling ca-

pacitor, thus eliminating the usual transformer.

No current limitation is provided on the output stage

of LS1240A, so a minimum load DC of 50

Ω is ad-

viced, in series with a proper capacitor.

The two tone frequencies generated are switched

by an internal oscillator in a fast sequence and made

audible across an output amplifier in the loud-

speaker, both tone frequencies and the switching

frequency can be externally adjusted.

The supply voltage is obtained from the AC ring sig-

nal and the circuit is designed so that noise on the

line or variations of the ringing signal cannot affect

correct operation of the device.

SO8

Minidip

ORDERING NUMBERS

Minidip

SO8

LS1240A

LS1240AD1

PIN CONNECTION (top view)

1/7