August 2006 Rev 2 1/9
9
LS1240
Electronic two-tone ringer
Features
■Low current consumption, in order to allow the
parall el oper at ion of 4 device s
■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
Description
LS1240 is a monolithic integrated circuit designed
to replace the mechanical bell in telephone sets in
connection with an electro-acoustical conv erter . 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.
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.
Pin connection (top view)
Minidip
SO8
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Block diagram and test circuit LS1240
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1 Block diagram and test circuit
Figure 1. LS1240 block diagram
Figure 2. Test circuit
Rectifier
bridge Thresho ld circu it
with hysteresis
Output
stage
Tone frequency
generator
Switching
generator
frequency
8765
4321
Telephone
line Rectifier
capacitor N.C. Buzzer
Output frequency
contro l res is tor
Sweep rate
control capacitor
GND
Telephone
line
+
-
R1 =2.72 ⋅ 104
f1 (Hz)⋅(1− 0. 04 ln f1
1943) f2 = 0.725 f1 fSWEEP =750
C1 (nF)
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LS1240 Electrical characteristics
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2 Electrical characteristics
Tamb = 25°C, VS = applied between pins 7-2 unless otherwise specified.
Table 1. Absolute maximum ratings
Symbol Parameter Value Unit
VAB Calling voltage (f = 50 Hz) continuous 120 Vms
VAB Calling voltage (f = 50 Hz) 5s ON/10s OFF 200 Vms
DC Supply current 30 mA
TOP Operating temperature -40 to 70 °C
Tstg Storage and junction temperature -65 to +150 °C
Table 2. Thermal data
Symbol Parameter Value Unit
Rthj-amb Maximum thermal resistance junction-ambient 100 °C/W
Table 3. Electrical characteristics
Symbol Parameter Test conditions Min. Typ. Max. unit
VSSupply vol tag e 26 V
IBCurrent consumption
without laod (pins 8-1) V8-1 = 9.3 to 25 V 1.5 1.8 mA
VON Activation voltage 12.2 13.2 V
VOFF Sustaining voltage 8 9 V
RD
Differential resistance
in OFF conditions
(pins 8-1) 6.4 kΩ
VOUT Output voltage swing VS-5 V
IOUT Short circuit current
(pins 5-2) VS = 20V RL = 250Ω70 mA
AC operation
f1
f2
Output frequencies
fOUT1
fOUT2
VS = 26V, R1 = 14Ω
VS = 0V
VS = 6V 1.74
1.22 2.14
1.6 kHz
1.33 1.43
Programmi ng res ist or
range 856kW
Sweep frequency R1 = 14 kΩ, C1 =
100 nF 5.25 7.5 9.75 Hz
fOUT1
fOUT2
------------
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Application schematics LS1240
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3 Application schematics
Figure 3. Typical application with buzzer
Figure 4. Typical application with loudspeaker (no transformer needed)
C1 such that ⏐ZLOA D ⏐ > 1 ΚΩ
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LS1240 Package mechanical data
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4 Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK®
packages. These packages have a Lead-free second level interconnect . The category of
second Level Interconnect ismarked on the package and on the inner box label, in
compliance with JEDEC Standard JESD97. The maximum ratings related to soldering
conditions are also marked on the inner box label. ECOPA CK is an ST tra demark.
ECOPACK specifications are available at: www.st.com.
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Package mechanical data LS1240
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Figure 5. Minidip package mechanicla drawing
Table 4. Minidip package dimensions
Dim.
mm inch
Min. Typ. Max. Min. Typ. Max.
A 3.32 0.131
a1 0.51 0.020
B 1.15 1.65 0.045 0.065
b 0.356 0.55 0.014 0.022
b1 0.204 0.304 0.008 0.012
D 10.92 0.430
E 7.95 9.75 0.313 0.384
e 2.54 0.100
e3 7.62 0.300
e4 7.62 0.300
F6.60.260
I 5.08 0.200
L 3.18 3.81 0.125 0.150
Z 1.52 0.060
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LS1240 Package mechanical data
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Figure 6. SO8 mechanical drawing
Table 5. SO8 package dimensions
Dim.
mm inch
Min. Typ. Max. Min. Typ. Max.
A 1.75 0.069
a1 0.1 0.25 0.004 0.010
a2 1.65 0.065
a3 0.65 0.85 0.026 0.033
b 0.35 0.48 0.014 0.019
b1 0.19 0.25 0.007 0.010
C 0.25 0.50 0.010 0.020
c1 45° (typ.)
D(1) 4.8 5.0 0.189 0.197
E 5.8 6.2 0.228 0.244
e 1.27 0.050
e3 3.81 0.150
F(1) 3.8 4.0 0.15 0.157
L 0.4 1.27 0.016 0.050
M0.60.024
S8° (max.)
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Ordering information LS1240
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5 Ordering information
6 Revision history
Table 6. Order codes
Part number Package
LS1240A Minidip
LS1240AD1 SO8
E-LS1240A(1)
1. ECOPACK® (see
Chapter 4
)
Minidip
E-LS1240AD1(1) SO8
Table 7. Document revision history
Date Revision Changes
15-Jul-1998 1 Initial release.
23-Aug-2006 2 Updated the document to reflect the fact that packages are leadfree
and part numbers have changed.
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LS1240
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