PBL3766SLASH6 datasheet(13/18 Pages) ERICSSON

13 / 18 page

PBL 3766

4-13

A 2 x 900 ohm resistive feed substitu-

tes for the active state constant current

feed.

The following paragraphs describe the

PBL 3766 battery feed system in detail.

Case 1: SLIC in the Active State

TRdc < VSGRef

In the active state C1 = 0 and C2 = 1.

In this operating state tip to ring voltages

TRdc less than VSGRef, cause the block

titled saturation guard in figure 12 to be

disabled, i.e. its output is equal to zero.

For this case circuit analysis yields:

2500

Ldc =

DC + 41700

where

Ldc

= the constant loop current. I

Ldc is in

amperes for R

DC in ohms.

DC = the programming resistance, in

ohms, which sets the constant loop

current magnitude.

When the desired constant loop current

is known, R

DC is calculated from

2500

DC =

- 41700

Ldc

Capacitor C

DC, connected between the

RDC terminal and ground, removes noise

and vf signals from the battery feed

control loop. C

DC is calculated according

 11 

DC =· 



π · f

41700

DC 

where

=5 Hz

DC =

constant current programming

resistance in ohms

DC =

filter capacitor in farads

Case 2: SLIC in the Active State

TRdc > VSGRef

In the active state C1 = 0 and C2 = 1.

When the tip to ring dc voltage

approaches the V

Bat supply voltage, the

saturation guard block shown in figure 12

is engaged and will limit the two-wire

voltage to a small additional increase

beyond the saturation guard threshold,

SGref. This leaves a sufficient voltage

margin to the V

Bat supply to maintain

distortion free vf transmission through the

line drive amplifiers. The saturation guard

feature makes on-hook transmission

possible in the active state.

The tip to ring voltage at which the

saturation guard becomes active, V

SGRef,

can be calculated from

5·105

SGRef = 12.5 +

25000 + R

where

SGRef

is in volts for R

SG in ohms

SG is a resistor connected between

terminal RSG and V

EE (-5 V).

SG =

open circuit yields V

SGRef = 12.5 V

SG =

0 ohm yields V

SGRef = 32.5 V

The loop voltage, V

TRdc, as a function of

the loop resistance, R

L, for VTRdc > VSGRef is

described by

16.66 + 5.00·105/(25000 + R

SG)

TRdc =

· R

L + (RDC + 41700) / 600

from which the open loop voltage (I

L = 0)

is calculated to

5.00·105

TRdc = 16.66 +

25000 + R

For R

SG = open circuit, the on-hook tip

to ring dc voltage is 16.7 V, which is

compatible with V

Bat in the -24 V to -28 V

range.

For R

SG = 0 ohm, the on-hook tip to ring

dc voltage is 36.7 V, which is compatible

with V

Bat in the -42 V to -58 V range.

For intermediate battery voltage values,

Bat, RSG can be calculated from

5.00·105

SG =

- 25000

TRdc -16.66

where

is in ohms for V

TRdc in volts

TRdc is the open loop tip to ring

voltage.Let V

TRdc = |VBat| - 8 V to allow

distortion free transmission of a 3.1 V

pk vf

signal in the on-hook mode. The 8 V

margin may be reduced if a vf signal of

less than 3.1 Vpk is to be transmitted in

the on-hook mode.

Case 3: SLIC in the Stand-by State

In the stand-by state C1 = 1 and C2 = 1.

With the SLIC operating in the stand-by,

power saving state the tip and ring drive

amplifiers are disconnected and a

resistive battery feed is engaged. The

loop current can be calculated from

Bat - 3 V

Ldc ≈

L + 1800 Ω

where

Ldc

= loop current

= loop resistance

Bat

= battery supply voltage

-3 V

= voltage drop across internal

transistors

1800

Ω = feed resistance (900 Ω on the

tip side, 900

Ω on the ring side)

PBL 3766 Power Dissipation and

Derating

The tip to ring short circuit total power

dissipation, P

ShTot, is

ShTot = ILSh · (|VBat| - ILSh · 2RF) + POnAct

where

LSh = 2500/(41700 + RDC) is the short

circuit loop current

OnAct is the active state on-hook dissipa-

tion, typically 160 mW V

Bat = -48V

The permissible maximum device

dissipation is 1.5 W. The maximum

allowable junction temperature is 140

°C

for normal reliability requirements and

110

°C for extreme reliability requirements.

The junction temperature is calculated

from

J = PShTot · (θJP + θPA) + TAmb,

J < 140 °C

where

JP = θJP28plcc = θJP22dip is the thermal

resistance from junction to all VBAT

terminals, typically 10

°C/W θ

PA is the

thermal resistance from all VBAT terminals

to ambient. The

PA value will be depend-

ent on line-card thermal design.

Amb is the ambient temperature in °C.

Loop Monitoring Functions

Overview

The PBL 3766 SLIC contains detectors for

loop current and ring trip. These two

detectors report their status via the shared

DET

output. A triggered detector is

indicated by a logic low level at the DET

output. The detector to be connected to

the DET output is selected via the control

interface C1 and C2. Refer to section

Control Inputs for a description of the

control interface. Enable input E0 sets the

DET

output to either active or high imped-

ance state.

Loop Current Detector

The loop current detector is connected to

the DET output in the stand-by (C2, C1 =

1, 1) and the active (C2, C1 = 1, 0) states.

Refer to figure 14.

The loop current value, I

LThOff, at which

the loop current detector changes from

indicating on-hook to indicating off-hook is

internally programmed to 8.0 mA.

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