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L3845B

TRUNK INTERFACE

STMicroelectronics 

L3845

DC ELECTRICAL CHARACTERISTICS (IL = 10 mA to 100 mA, R1 = 56 Ω, S1 = Open, Tamb = + 25 °C,

unless otherwise specified)

Symbol

VL

Parameter

Line Voltage

(normal mode)

VLP

Line Voltage

(pulse mode)

Ihn

ON/OFF-Hook

Line Current Detection

Threshold

Ihf

OFF/ON-Hook

Line Current Detection

Threshold

IOUT

OFF-Ho ok

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)

Test Condition

PULSE = Open

IL = 10 mA

IL = 20 mA

IL = 100 mA

PULSE = V–

IL = 20 mA

IL = 35 mA

IL = 80 mA

IL = 10 mA

IL ≥ 20 mA

IL = 100 mA

Pulse = V–

Min. Typ. Max. Unit

5

V

6

V

12

V

4

V

5.5

V

9.5

V

6.5

9.5

mA

5

9.2

mA

1.5

mA

2

mA

0.8

V

20

µA

3

µA

AC ELECTRICAL CHARACTERISTICS (IL = 10mA to 100mA, R1 = 56Ω, R2 = 470KΩ, R3 = 130 KΩ,

Tamb = + 25 °C, unless otherwise specified)

Symbol

ZL

Parameter

AC Line Impedance

Sending/Receiving Distortion

Sending/Receiving Distortion

Sending/Receiving Distortion

(*) Not tested, guaranteed only by design.

Test Condition

S1 = Open, S2 = Open

C1 = 2.2mF

f = 1KHz

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

Min. Typ. Max. Unit

20

KΩ

2

%

2

%

2(*)

%

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.

3/7

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