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L3845
TRUNK INTERFACE
ON CHIP POLARITY GUARD
MEETS DC LINE CHARACTERISTICS OF
EITHER CCITT AND EIA RS 464 SPECS
PULSE FUNCTION
HIGH AC IMPEDANCE
OFF HOOK-STATUS DETECTION OUTPUT
LOW EXTERNAL COMPONENT COUNT
DESCRIPTION
The circuit provides DC loop termination for ana-
log trunk lines.
The V-I characteristics is equivalent to a fixed
voltage drop (zener like characteristic) in series
with an external resistance that determines the
slope of the DC characteristic.
An external low voltage electrolytic capacitor
causes the circuit to exhibit a very high imped-
ance to all AC signal above a minimum frequency
that is determined by the capacitor itself and by a
20 K nominal resistor integrated on the chip.
The Off-Hook status is detected all the time a
typic of 8 mA is flowing into the circuit. In this con-
dition a constant current generator is activated to
supply an external device (typically an optocou-
pler) without affecting the AC characteristic of the
circuit.
When Pulse Dialing is required the PULSE input
(pin 3) connected to V- causes the device to re-
duce the fixed DC voltage drop and to exhibit a
pure resistive impedance equal to the external re-
sistor.
This is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
September 2003
POLARITY
GUARD
DC LINE
TERMINATION
OF HOOK
DETECTION
CIRCUIT
1
7
8
3
4
IN1
IN2
5
6
2
ACT
DCT
V-
R2
R3
R1
S1
C1
S2
V+
PULSE
HD0
D96TL263
BLOCK DIAGRAM
Minidip SO8 SO20W
(12+4+4)
ORDERING NUMBERS:
L3845B L3845D L3845-20
1/8
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Value
Unit
V
L
Max Line Voltage (pulse duration 10 ms max)
20
V
I
L
Max Line Current
150
mA
P
tot
Total Power Dissipation at Tamb = 70
C
800
mW
T
op
Operating Temperature
40 to + 70
C
T
srg
, T
j
Storage and Junction Temperature
55 to + 150
C
THERMAL DATA
Symbol
Parameter
Minidip
SO8
SO20
Unit
R
th j-amb
Thermal Resistance Junction-ambient (*) Max.
80
140 to 180
50 to 70
C/W
(*) Mounted on FR4 Boards
PIN CONNECTION (Top view)
PULSE
HD0
NC
SUBS
SUBS
SUBS
SUBS
NC
ACT
V+
NC
SUBS
SUBS
SUBS
SUBS
NC
IN1
V-
1
3
2
4
5
6
7
8
9
18
17
16
15
14
12
13
11
19
10
20
DCT
IN2
SO20
SO20
IN1
V-
PULSE
HD0
1
3
2
4
ACT
DCT
IN2
V+
8
7
6
5
DIP8
MINIDIP and SO8
SUBS = the pin is electrically and thermally in good contact with the chip sustrate. Connect to PCB copper tracks, for heat dissipation the
tracks shall preferably be electrically connected to pin 20 (internally bonded to the chip substrate) or left floating. A higher track
density and/or area assures a R
th j-amb
towards the lower limit.
L3845
2/8
DC ELECTRICAL CHARACTERISTICS (I
L
= 10 mA to 100 mA, R
1
= 56
, S
1
= Open, T
amb
= + 25
C,
unless otherwise specified)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
V
L
Line Voltage
(normal mode)
PULSE = Open
IL = 10 mA
I
L
= 20 mA
I
L
= 100 mA
5
6
12
V
V
V
V
LP
Line Voltage
(pulse mode)
PULSE = V
I
L
= 20 mA
I
L
= 35 mA
I
L
= 80 mA
4
5.5
9.5
V
V
V
I
hn
ON/OFF-Hook
Line Current Detection
Threshold
6.5
9.5
mA
I
hf
OFF/ON-Hook
Line Current Detection
Threshold
5
9.2
mA
I
OUT
OFF-Hook
Output Drive Current at Pin
HDO
IL = 10 mA
I
L
20 mA
1.5
1.8
mA
mA
V
PM
Pulse Input Low Voltage
0.8
V
I
PM
Pull-up Input Current at Pin
PULSE (pulse mode)
IL = 100 mA
Pulse = V
20
A
I
NM
Imput Current at Pin Pulse
(normal mode)
3
A
AC ELECTRICAL CHARACTERISTICS (I
L
= 10mA to 100mA, R
1
= 56
, R
2
= 470K
, R
3
= 130 K
,
T
amb
= + 25
C, unless otherwise specified)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
Z
L
AC Line Impedance
S
1
= Open, S
2
= Open
C
1
= 2.2mF
f = 1KHz
20
K
Sending/Receiving Distortion
S
1
= Open, S
2
= Open
f = 1KHz
V
AC-L
= 775mVrms
I
L
= 15 to 100mA
2
%
Sending/Receiving Distortion
S
1
= Closed; S
2
= Open
V
AC-L
= 1.3Vrms
2
%
Sending/Receiving Distortion
S
1
= Open; S
2
= Closed
V
AC-L
= 1.9Vrms
2(*)
%
(*) Not tested, guaranteed only by design.
APPLICATION INFORMATION
With the use of this circuit it is possible to termi-
nate an analog trunk so that all the DC current
component is flowing in the TRUNK TERMINA-
TION CIRCUIT while the AC component is de-
coupled with a low voltage capacitor and can be
used with a small and low cost audio coupler
transformer to provide the AC balancing termina-
tion and two to four wire conversion.
Therefore it is usefull both for MODEM and PABX
systems.
Figure 1 gives the typical application circuit ; it is
worth to note that the TRUNK TERMINATION
CIRCUIT, together with the LS5018 transient sup-
pressor provides a compact and low cost module
fully protected against lightning or overvoltages
frequently present on telephone lines.
The PULSE input when connected to V- allows
the device to reduce the Line Voltage and to
show a resistive impedance equal to R1 to the
line. When PULSE input is left open, this function
is disable.
L3845
3/8
Figure 1: Typical Application.
L3845
4/8
OUTLINE AND
MECHANICAL DATA
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
F
6.6
0.260
I
5.08
0.200
L
3.18
3.81
0.125
0.150
Z
1.52
0.060
Minidip
L3845
5/8
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
0.5
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
M
0.6
0.024
S
8
(max.)
(1) D and F do not include mold flash or protrusions. Mold flash or
potrusions shall not exceed 0.15mm (.006inch).
SO8
OUTLINE AND
MECHANICAL DATA
L3845
6/8
1
1
0
11
20
A
e
B
D
E
L
K
H
A1
C
SO20MEC
h x 45
SO20
DIM.
mm
inch
MIN.
TYP.
MAX.
MIN.
TYP.
MAX.
A
2.35
2.65
0.093
0.104
A1
0.1
0.3
0.004
0.012
B
0.33
0.51
0.013
0.020
C
0.23
0.32
0.009
0.013
D
12.6
13
0.496
0.512
E
7.4
7.6
0.291
0.299
e
1.27
0.050
H
10
10.65
0.394
0.419
h
0.25
0.75
0.010
0.030
L
0.4
1.27
0.016
0.050
K
0 (min.)8 (max.)
OUTLINE AND
MECHANICAL DATA
L3845
7/8
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences
of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is
granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are
subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products
are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.
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L3845
8/8