®
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
Minidip
SO8
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
BLOCK DIAGRAM
ORDERING NUMBERS:
L3845B
L3845D
b
O
so
te
le
IN1
r
P
1
7
uc
od
s)
t(
bs
-O
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.
et
l
o
P
e
od
r
s)
t(
uc
L3845-20
SO20W
(12+4+4)
8
3
V+
PULSE
POLARITY
GUARD
DC LINE
TERMINATION
OF HOOK
DETECTION
CIRCUIT
4
HD0
IN2
5
ACT
R2
R3
C1
S1
S2
6
DCT
2
V-
R1
D96TL263
September 2003
1/8
This is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
L3845
ABSOLUTE MAXIMUM RATINGS
Symbol
V
L
I
L
P
tot
T
op
T
srg
, T
j
Parameter
Max Line Voltage (pulse duration 10 ms max)
Max Line Current
Total Power Dissipation at Tamb = 70
°C
Operating Temperature
Storage and Junction Temperature
Value
20
150
800
– 40 to + 70
– 55 to + 150
Unit
V
mA
mW
°C
°C
PIN CONNECTION
(Top view)
SO20
PULSE
HD0
NC
SUBS
SUBS
SUBS
SUBS
NC
ACT
DCT
1
2
3
4
5
6
7
8
9
10
SO20
MINIDIP and SO8
20
19
18
17
16
15
14
13
12
11
V-
IN1
NC
SUBS
SUBS
SUBS
SUBS
NC
V+
IN1
V-
PULSE
1
2
IN2
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.
THERMAL DATA
Symbol
R
th j-amb
(*) Mounted on FR4 Boards
O
so
b
te
le
r
P
uc
od
s)
t(
bs
-O
et
l
o
HD0
P
e
3
4
od
r
8
7
6
5
s)
t(
uc
V+
IN2
DCT
ACT
DIP8
Parameter
Max.
Minidip
80
SO8
140 to 180
SO20
50 to 70
Unit
°C/W
Thermal Resistance Junction-ambient (*)
2/8
L3845
DC ELECTRICAL CHARACTERISTICS
(I
L
= 10 mA to 100 mA, R
1
= 56
Ω,
S
1
= Open, T
amb
= + 25
°C,
unless otherwise specified)
Symbol
V
L
Parameter
Line Voltage
(normal mode)
Test Condition
PULSE = Open
IL = 10 mA
I
L
= 20 mA
I
L
= 100 mA
PULSE = V
–
I
L
= 20 mA
I
L
= 35 mA
I
L
= 80 mA
6.5
Min.
Typ.
Max.
5
6
12
4
5.5
9.5
9.5
Unit
V
V
V
V
V
V
mA
V
LP
Line Voltage
(pulse mode)
I
hn
ON/OFF-Hook
Line Current Detection
Threshold
OFF/ON-Hook
Line Current Detection
Threshold
OFF-Hook
Output Drive Current at Pin
HDO
Pulse Input Low Voltage
Pull-up Input Current at Pin
PULSE (pulse mode)
Imput Current at Pin Pulse
(normal mode)
IL = 100 mA
Pulse = V
–
IL = 10 mA
I
L
≥
20 mA
I
hf
5
9.2
mA
I
OUT
1.5
1.8
V
PM
I
PM
I
NM
AC ELECTRICAL CHARACTERISTICS
(I
L
= 10mA to 100mA, R
1
= 56Ω, R
2
= 470KΩ, R
3
= 130 KΩ,
T
amb
= + 25
°C,
unless otherwise specified)
Symbol
Z
L
Parameter
AC Line Impedance
S
1
= Open, S
2
= Open
C
1
= 2.2mF
f = 1KHz
S
1
= Open, S
2
= Open
f = 1KHz
V
AC-L
= 775mVrms
I
L
= 15 to 100mA
S
1
= Closed; S
2
= Open
V
AC-L
= 1.3Vrms
S
1
= Open; S
2
= Closed
V
AC-L
= 1.9Vrms
2
2(*)
Sending/Receiving Distortion
Sending/Receiving Distortion
Sending/Receiving Distortion
(*) Not tested, guaranteed only by design.
b
O
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.
so
te
le
r
P
uc
od
s)
t(
bs
-O
Test Condition
et
l
o
P
e
Min.
od
r
Typ.
20
s)
t(
uc
0.8
20
3
V
Max.
mA
mA
µA
µA
Unit
KΩ
2
%
%
%
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.
3/8
L3845
Figure 1:
Typical Application.
O
so
b
te
le
r
P
uc
od
s)
t(
bs
-O
et
l
o
P
e
od
r
s)
t(
uc
4/8
L3845
mm
DIM.
MIN.
A
a1
B
b
b1
D
E
e
e3
e4
F
I
L
Z
3.18
7.95
2.54
7.62
7.62
6.6
5.08
3.81
1.52
0.125
0.51
1.15
0.356
0.204
1.65
0.55
0.304
10.92
9.75
0.313
0.100
0.300
0.300
0.260
0.200
0.150
0.060
TYP.
3.32
0.020
0.045
0.014
0.008
0.065
0.022
0.012
0.430
0.384
MAX.
MIN.
TYP.
0.131
MAX.
inch
OUTLINE AND
MECHANICAL DATA
O
so
b
te
le
r
P
uc
od
s)
t(
bs
-O
et
l
o
P
e
Minidip
od
r
s)
t(
uc
5/8
