STMICROELECTRONICS E

LS1240
Electronic two-tone ringer
Features
■
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.
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.
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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.
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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.
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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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Pin connection (top view)
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Block diagram and test circuit
1
LS1240
Block diagram and test circuit
Figure 1.
LS1240 block diagram
Telephone
line
8
Rectifier
capacitor
7
Rectifier
bridge
1
Telephone
line
Figure 2.
N.C.
Test circuit
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Buzzer
5
6
+
-
Threshold circuit
with hysteresis
Output
Switching
frequency
generator
Tone frequency
generator
2
stage
3
GND
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Sweep rate
control capacitor
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Output frequency
control resistor
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R1 =
2.72 ⋅ 104
f1
⋅ ( 1 − 0.04 ln
)
1943
f1 (Hz)
f2 = 0.725 f1
fSWEEP =
750
C1 (nF)
LS1240
2
Electrical characteristics
Electrical characteristics
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
Value
Unit
100
°C/W
Table 2.
Thermal data
Symbol
Rthj-amb
Parameter
Maximum thermal resistance junction-ambient
Tamb = 25°C, VS = applied between pins 7-2 unless otherwise specified.
Table 3.
Symbol
Parameter
VS
Supply voltage
IB
Current consumption
without laod (pins 8-1)
VON
Activation voltage
VOFF
Sustaining voltage
RD
Differential resistance
in OFF conditions
(pins 8-1)
VOUT
Output voltage swing
IOUT
Short circuit current
(pins 5-2)
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Output frequencies
fOUT1
fOUT2
VS = 26V, R1 = 14Ω
VS = 0V
VS = 6V
f OUT1
-----------f OUT2
Programming resistor
range
R1 = 14 kΩ, C1 =
100 nF
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Typ.
Max.
unit
26
V
1.8
mA
12.2
13.2
V
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V
P
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let
so
VS = 20V RL = 250Ω
Sweep frequency
Min.
V8-1 = 9.3 to 25 V
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Test conditions
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AC operation
f1
f2
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Electrical characteristics
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1.5
6.4
kΩ
VS-5
V
70
mA
1.74
1.22
2.14
1.6
1.33
1.43
8
56
kW
9.75
Hz
5.25
7.5
kHz
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Application schematics
3
LS1240
Application schematics
Figure 3.
Figure 4.
Typical application with buzzer
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Typical application with loudspeaker (no transformer needed)
C1 such that ⏐ZLOAD ⏐ > 1 ΚΩ
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LS1240
4
Package mechanical data
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. ECOPACK is an ST trademark.
ECOPACK specifications are available at: www.st.com.
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Package mechanical data
Table 4.
LS1240
Minidip package dimensions
mm
inch
Dim.
Min.
A
Typ.
Typ.
Max.
0.131
a1
0.51
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
0.020
10.92
E
7.95
0.430
9.75
0.313
0.384
e
2.54
0.100
e3
7.62
0.300
e4
7.62
0.300
F
6.6
I
5.08
L
3.18
3.81
Z
0.125
1.52
Figure 5.
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Minidip package mechanicla drawing
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Min.
3.32
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Max.
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0.260
0.200
0.150
0.060
LS1240
Package mechanical data
Table 5.
SO8 package dimensions
mm
inch
Dim.
Min.
Typ.
Max.
A
Min.
Typ.
1.75
a1
0.1
0.069
0.25
a2
Max.
0.004
0.010
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
E
5.8
6.2
0.228
0.197
e
1.27
0.050
e3
3.81
0.150
F(1)
3.8
4.0
0.15
L
0.4
1.27
0.016
0.6
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0.244
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0.157
0.050
0.024
8° (max.)
Figure 6.
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SO8 mechanical drawing
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Ordering information
5
LS1240
Ordering information
Table 6.
Order codes
Part number
Package
LS1240A
Minidip
LS1240AD1
SO8
(1)
E-LS1240A
Minidip
E-LS1240AD1(1)
SO8
®
1. ECOPACK (see Chapter 4)
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Revision history
Table 7.
Document revision history
Date
Revision
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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