L3845
TRUNK INTERFACE
ON CHIP POLARITYGUARD
MEETS DC LINE CHARACTERISTICS OF
EITHER CCITTAND EIA RS 464 SPECS
PULSE FUNCTION
HIGHAC IMPEDANCE
OFF HOOK-STATUS DETECTION OUTPUT
LOW EXTERNAL COMPONENT COUNT
DESCRIPTION
The circuit provides DC loop termination for ana-
log trunklines.
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 determinedby the capacitor itself and by a
20 K nominalresistorintegratedon thechip.
The Off-Hook status is detected all the time a
typicof 8 mA is flowinginto the circuit. In this con-
dition a constant current generator is activated to
supply an external device (typically an optocou-
pler) without affectingthe AC characteristicof 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 impedanceequal to the external re-
sistor.
This is advanced information on a new product now in development or undergoingevaluation. Details are subject to change without notice.
June 1996
POLARITY
GUARD DC
LINE
TERMINATION OF
HOOK
DETECTION
CIRCUIT
1
7
8
3
4
IN1
IN2
562
ACT DCT V-
R2 R3
R1
S1 C1
S2
V+
PULSE
HD0
D96TL263
BLOCK DIAGRAM
Minidip SO8
ORDERING NUMBERS:
L3845B L3845D
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ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
VLMax Line Voltage (pulse duration 10 ms max) 20 V
ILMax Line Current 150 mA
Ptot Total Power Dissipation at Tamb = 70 °C 800 mW
Top Operating Temperature – 40 to + 70 °C
Tsrg,T
jStorage and Junction Temperature – 55 to + 150 °C
THERMAL DATA
Symbol Parameter Minidip SO8 Unit
Rth j-amb Thermal Resistance Junction-ambient (*) Max. 80 140 to 180 °C/W
(*) Mounted on FR4 Boards
PIN CONNECTION (Topview)
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DC ELECTRICAL CHARACTERISTICS (IL= 10mA to100 mA, R1=56Ω
,S
1= Open, Tamb =+25°
C,
unless otherwisespecified)
Symbol Parameter Test Condition Min. Typ. Max. Unit
VLLine Voltage
(normal mode) PULSE = Open
IL = 10 mA
IL=20mA
I
L= 100 mA
5
6
12
V
V
V
VLP Line Voltage
(pulse mode) PULSE = V–
IL=20mA
I
L=35mA
I
L=80mA
4
5.5
9.5
V
V
V
Ihn ON/OFF-Hook
Line Current Detection
Threshold
6.5 9.5 mA
Ihf OFF/ON-Hook
Line Current Detection
Threshold
59.2mA
I
OUT OFF-Hook
Output Drive Current at Pin
HDO
IL = 10 mA
IL≥20 mA 1.5
2mA
mA
VPM Pulse Input Low Voltage 0.8 V
IPM Pull-up Input Current at Pin
PULSE (pulse mode) IL = 100 mA
Pulse = V–20 µA
INM Imput Current at Pin Pulse
(normal mode) 3µA
AC ELECTRICAL CHARACTERISTICS (IL= 10mA to 100mA, R1=56Ω,R
2=470KΩ,R
3= 130 KΩ,
Tamb =+25°C, unlessotherwise specified)
Symbol Parameter Test Condition Min. Typ. Max. Unit
ZLAC Line Impedance S1= Open, S2= Open
C1= 2.2mF
f = 1KHz 20 KΩ
Sending/Receiving Distortion S1= Open, S2= Open
f = 1KHz
VAC-L = 775mVrms
IL= 15 to 100mA 2%
Sending/Receiving Distortion S1= Closed; S2= Open
VAC-L = 1.3Vrms 2 %
Sending/Receiving Distortion S1= Open; S2= Closed
VAC-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-
tionand two to four wire conversion.
Thereforeit is usefull both for MODEMand PABX
systems.
Figure 1 gives the typical application circuit ; it is
worth to note that the TRUNK TERMINATION
CIRCUIT, togetherwith the LS5018transient sup-
pressor provides a compact and low cost module
fully protected against lightning or overvoltages
frequentlypresenton telephonelines.
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.
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Figure 1: TypicalApplication.
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MINIDIP PACKAGE 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 0260
i 5.08 0.200
L 3.18 3.81 0.125 0.150
Z 1.52 0.060
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SO8 PACKAGE MECHANICAL DATA
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 45o(typ.)
D 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 3.8 4.0 0.150 0.157
L 0.4 1.27 0.016 0.050
M 0.6 0.024
S8
o
(max.)
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Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics 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 isgranted by implication or otherwise under any patent or patent rights
of SGS-THOMSON Microelectronics. Specifications mentioned in this publication are subject to change without notice.
This publication supersedes and replaces all information previously supplied. SGS-THOMSON Microelectronics prod-
ucts are not authorized for use as critical components in life support devices or systems without express written ap-
proval of SGS-THOMSON Microelectronics.
1994 SGS-THOMSON Microelectronics - All Rights Reserved
SGS-THOMSON Microelectronics GROUP OF COMPANIES
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