SGS Thomson Microelectronics L3845B, L3845D Datasheet

ON CHIP POLARITYGUARD MEETS DC LINE CHARACTERISTICS OF
EITHER CCITTANDEIARS464SPECS PULSE FUNCTION HIGHAC IMPEDANCE OFFHOOK-STATUS DETECTION OUTPUT LOW EXTERNAL COMPONENT COUNT
DESCRIPTION
The circuit provides DC loop termination for ana­log 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 imped­ance to all AC signal above a minimum frequency that is determinedby the capacitor itselfand by a 20 Knominalresistor integrated on thechip.
The Off-Hook status is detected all the time a typic of 8 mA is flowinginto thecircuit. In this con­dition a constant current generator is activated to
L3845
TRUNK INTERFACE
Minidip SO8
ORDERING NUMBERS:
L3845B L3845D
supply an external device (typically an optocou­pler) without affectingthe AC characteristicof the circuit.
When Pulse Dialing is required the PULSE input (pin 3) connected to V- causes the device to re­duce the fixed DC voltage drop and to exhibit a pure resistive impedanceequal to the externalre­sistor.
BLOCK DIAGRAM
8
1
IN1
DC
POLARITY
GUARD
7
IN2
562
ACT DCT V-
R2 R3
S1
June 1996
This is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
LINE
TERMINATION OF
S2
C1
R1
DETECTION
HOOK
CIRCUIT
D96TL263
V+
3
PULSE
4
HD0
1/7
L3845
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
V
L
I
L
P
tot
T
op
T
srg,Tj
PIN CONNECTION (Topview)
Max Line Voltage (pulse duration 10 ms max) 20 V Max Line Current 150 mA Total Power Dissipation at Tamb = 70 °C 800 mW Operating Temperature – 40 to + 70 °C Storage and Junction Temperature – 55 to + 150 °C
THERMAL DATA
Symbol Parameter Minidip SO8 Unit
R
th j-amb
(*) Mounted on FR4 Boards
2/7
Thermal Resistance Junction-ambient (*) Max. 80 140 to 180°C/W
L3845
DC ELECTRICALCHARACTERISTICS
= 10 mA to 100 mA, R1=56Ω,S1= Open, T
(I
L
=+25°C,
amb
unless otherwisespecified)
Symbol Parameter Test Condition Min. Typ. Max. Unit
V
L
Line Voltage (normal mode)
V
LP
Line Voltage (pulse mode)
I
hn
ON/OFF-Hook Line CurrentDetection Threshold
I
hf
OFF/ON-Hook Line CurrentDetection Threshold
I
OUT
OFF-Hook Output Drive Current at Pin HDO
V
PM
I
PM
Pulse Input Low Voltage 0.8 V Pull-up Input Current at Pin
PULSE (pulse mode)
I
NM
Imput Current at Pin Pulse (normal mode)
PULSE = Open IL = 10 mA I
=20mA
L
I
= 100 mA
L
PULSE = V
IL=20mA I
=35mA
L
I
=80mA
L
IL = 10 mA I
20 mA
L
IL = 100 mA Pulse = V
5 6
12
4
5.5
9.5
6.5 9.5 mA
59.2mA
1.5 2
20 µA
3
V V V
V V V
mA mA
µ
A
AC ELECTRICALCHARACTERISTICS (IL= 10mAto 100mA, R1=56Ω,R2=470KΩ,R3= 130K, T
=+25°C, unless otherwise specified)
amb
Symbol Parameter Test Condition Min. Typ. Max. Unit
Z
L
(*) Not tested,guaranteed only by design.
APPLICATIONINFORMATION
With the use of this circuit it is possible to termi­nate an analog trunk so that all the DC current component is flowing in the TRUNK TERMINA­TION CIRCUIT while the AC component is de­coupled with a low voltage capacitor and can be used with a small and low cost audio coupler transformer to provide the AC balancing termina­tion and two to four wire conversion.
Therefore it is usefull both for MODEMand PABX systems.
AC Line Impedance S1= Open, S2= Open
C
= 2.2mF
1
f = 1KHz
Sending/Receiving Distortion S
= Open, S2= Open
1
f = 1KHz V
= 775mVrms
AC-L
I
= 15 to 100mA
L
Sending/Receiving Distortion S
Sending/Receiving Distortion S
= Closed; S2= Open
1
V
= 1.3Vrms 2 %
AC-L
= Open; S2= Closed
1
V
= 1.9Vrms
AC-L
Figure 1 gives the typical application circuit ; it is worth to note that the TRUNK TERMINATION CIRCUIT,togetherwith the LS5018transient sup­pressor provides a compact and low cost module fully protected against lightning or overvoltages frequentlypresent on 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 PULSEinput is left open, this function is disable.
20 K
2%
2(*) %
3/7
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