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
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
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Value
Unit
V
AB
Calling Voltage (f = 50 Hz) Continuous
120
V
rms
V
AB
Calling Voltage (f = 50 Hz) 5s ON/10s OFF
200
V
rms
DC
Supply Current
30
mA
T
op
Operating Temperature
40 to + 70
C
T
stg
Storage and Junction Temperature
65 to + 150
C
THERMAL DATA
Symbol
Parameter
Value
Unit
R
th j-amb
Thermal Resistance Junction-ambient
Max
100
C/W
ELECTRICAL CHARACTERISTICS
(T
amb
= 25
C; V
s
= applied between pins 7-2 unless otherwise specified)
Symbol
Parameter
Test Conditions
Min.
Typ.
Max. Unit
V
s
Supply Voltage
26
V
I
B
Current Consumption without Load (pins 8-1)
V
8-1
= 9.3 to 25 V
1.5
1.8
mA
V
ON
Activation Voltage
12.2
13.2
V
V
OFF
Sustaining Voltage
8
9
V
R
D
Differential Resistance in OFF Condition (pins 8-1)
6.4
k
V
OUT
Output Voltage Swing
V
s
5
V
I
OUT
Short Circuit Current (pins 5-2)
V
s
= 20V
R
L
= 250
70
mA
AC OPERATION
f
1
f
2
Output Frequencies
f
out1
f
out2
V
s
= 26V, R
1
= 14k
V
s
= 0 V
V
s
= 6V
1.74
1.22
2.14
1.6
kHz
f
OUT1
f
OUT2
1.33
1.43
Programming Resistor Range
8
56
k
f
SWEEP
Sweep Frequency
R
1
= 14k
, C
1
= 100nF
5.25
7.5
9.75
Hz
LS1240A
3/7
Figure 2 : Typical Application with BUZZER
Figure 3 : Typical Application with Loudspeaker (no transformer needed)
C
1
such that
Z
LOAD
> 1
LS1240A
4/7
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