LS1240
Electronic two-tone ringer
Features
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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 over voltages little external
circuitry
Tone and switching frequencies adjustable by
external components
Integrated voltage and current hysteresis
Minidip
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■
Description
LS1240 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
(buzzer) or a dynamic loudspeaker.
The output current capability of LS1240 is higher
than the one of a standard ringer. To drive a
dynamic loudspeaker LS1240 can simply use a
decoupling capacitor, thus eliminating the usual
transformer.
No current limitation is provided on the output
stage of LS1240, so a minimum load DC of 50
Ω
is advised, in series with a proper capacitor.
Pin connection (top view)
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The two tone frequencies generated are switched
by an internal oscillator in a fast sequence and
are made audible across an output amplifier in the
loudspeaker. Both tone frequencies and the
switching frequency can be externally adjusted.
The supply voltage is obtained from the AC ring
signal and the circuit is designed so that noise on
the line or variations of the ringing signal cannot
affect correct operation of the device.
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August 2006
Rev 2
1/9
9
STMICROELECTRONICS [ STMICROELECTRONICS ]
