®
LS1240A
ELECTRONIC TWO - TONE RINGER
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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
Minidip
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.
PIN CONNECTION
(top view)
SO8
ORDERING NUMBERS
Minidip
LS1240A
SO8
LS1240AD1
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.
July 1998
1/7
STMICROELECTRONICS [ STMICROELECTRONICS ]
