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
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 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 condition a constant current generator is activated to
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BLOCK DIAGRAM
SO8
SO20W
(12+4+4)
ORDERING NUMBERS:
L3845B
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L3845D
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L3845-20
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supply an external device (typically an optocoupler) 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 reduce the fixed DC voltage drop and to exhibit a
pure resistive impedance equal to the external resistor.
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IN1
8
1
3
DC LINE
TERMINATION
POLARITY
GUARD
IN2
OF HOOK
DETECTION
CIRCUIT
7
5
6
2
ACT
DCT
V-
R2
R3
C1
4
V+
PULSE
HD0
S2
R1
S1
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
VL
IL
Ptot
Top
Tsrg, Tj
Value
Unit
Max Line Voltage (pulse duration 10 ms max)
Parameter
20
V
Max Line Current
Total Power Dissipation at Tamb = 70 °C
150
800
mA
mW
– 40 to + 70
– 55 to + 150
°C
°C
Operating Temperature
Storage and Junction Temperature
PIN CONNECTION (Top view)
SO20
MINIDIP and SO8
PULSE
1
20
V-
HD0
2
19
IN1
NC
3
18
NC
SUBS
4
17
SUBS
SUBS
5
16
IN1
1
SUBS
V-
2
3
SUBS
6
15
SUBS
PULSE
SUBS
7
14
SUBS
HD0
NC
8
13
NC
ACT
9
12
V+
DCT
10
11
IN2
SO20
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V+
7
IN2
6
DCT
5
ACT
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DIP8
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 Rth j-amb towards the lower limit.
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THERMAL DATA
Symbol
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Rth j-amb
2/8
Parameter
Thermal Resistance Junction-ambient (*)
(*) Mounted on FR4 Boards
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Max.
Minidip
SO8
SO20
Unit
80
140 to 180
50 to 70
°C/W
L3845
DC ELECTRICAL CHARACTERISTICS (IL = 10 mA to 100 mA, R1 = 56 Ω, S1 = Open, Tamb = + 25 °C,
unless otherwise specified)
Symbol
VL
VLP
Max.
Unit
Line Voltage
(normal mode)
Parameter
PULSE = Open
IL = 10 mA
IL = 20 mA
IL = 100 mA
Test Condition
Min.
Typ.
5
6
12
V
V
V
Line Voltage
(pulse mode)
PULSE = V–
IL = 20 mA
IL = 35 mA
IL = 80 mA
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
5
9.2
mA
IOUT
OFF-Hook
Output Drive Current at Pin
HDO
VPM
Pulse Input Low Voltage
IPM
Pull-up Input Current at Pin
PULSE (pulse mode)
INM
Imput Current at Pin Pulse
(normal mode)
IL = 10 mA
IL ≥ 20 mA
1.5
1.8
IL = 100 mA
Pulse = V–
mA
mA
P
e
let
V
20
µA
3
µA
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0.8
AC ELECTRICAL CHARACTERISTICS (I L = 10mA to 100mA, R1 = 56Ω, R2 = 470KΩ, R3 = 130 KΩ,
Tamb = + 25 °C, unless otherwise specified)
Symbol
Parameter
S1 = Open, S2 = Open
C1 = 2.2mF
f = 1KHz
)
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Sending/Receiving Distortion
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Sending/Receiving Distortion
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Sending/Receiving Distortion
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Test Condition
AC Line Impedance
ZL
Min.
Typ.
20
S1 = Open, S2 = Open
f = 1KHz
VAC-L = 775mVrms
IL = 15 to 100mA
S1 = Closed; S2 = Open
VAC-L = 1.3Vrms
S1 = Open; S2 = Closed
VAC-L = 1.9Vrms
Max.
Unit
KΩ
2
%
2
%
2(*)
%
(*) Not tested, guaranteed only by design.
APPLICATION INFORMATION
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 MODEM and PABX
systems.
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Figure 1 gives the typical application circuit ; it is
worth to note that the TRUNK TERMINATION
CIRCUIT, together with the LS5018 transient suppressor 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.
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4/8
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L3845
mm
inch
OUTLINE AND
MECHANICAL DATA
DIM.
MIN.
A
TYP.
MAX.
MIN.
3.32
TYP.
MAX.
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
E
10.92
7.95
9.75
0.430
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
Z
3.81
0.125
1.52
0.150
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0.060
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5/8
L3845
mm
DIM.
MIN.
TYP.
A
inch
MAX.
MIN.
TYP.
1.75
a1
0.1
0.25
a3
0.65
b
MAX.
0.069
0.004
0.010
0.85
0.026
0.033
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
a2
1.65
c1
OUTLINE AND
MECHANICAL DATA
0.065
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
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let
8 ° (max.)
S
(1) D and F do not include mold flash or protrusions. Mold flash or
potrusions shall not exceed 0.15mm (.006inch).
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L3845
mm
inch
OUTLINE AND
MECHANICAL DATA
DIM.
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
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t
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0˚ (min.)8˚ (max.)
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SO20
h x 45˚
A
e
A1
K
C
H
D
20
11
E
1
0
1
SO20MEC
7/8
L3845
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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.
The ST logo is a registered trademark of STMicroelectronics.
All other names are the property of their respective owners
© 2003 STMicroelectronics - All rights reserved
STMicroelectronics GROUP OF COMPANIES
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8/8
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