PBL 3766
saturation guard becomes active, VSGRef
can be calculated from
,
VBat
= battery supply voltage
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.
-3 V
= voltage drop across internal
transistors
5·105
VSGRef = 12.5 +
1800 Ω = feed resistance (900 Ω on the
tip side, 900 Ω on the ring side)
25000 + RSG
where
Case 1: SLIC in the Active State
VTRdc < VSGRef
PBL 3766 Power Dissipation and
Derating
VSGRef is in volts for RSG in ohms
RSG is a resistor connected between
terminal RSG and VEE (-5 V).
In the active state C1 = 0 and C2 = 1.
In this operating state tip to ring voltages
VTRdc 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:
The tip to ring short circuit total power
dissipation, PShTot, is
RSG = open circuit yields VSGRef = 12.5 V
RSG = 0 ohm yields VSGRef = 32.5 V
PShTot = ILSh · (|VBat| - ILSh · 2RF) + POnAct
where
The loop voltage, VTRdc, as a function of
the loop resistance, RL, for VTRdc > VSGRef is
described by
ILSh = 2500/(41700 + RDC) is the short
circuit loop current
2500
ILdc
=
RDC + 41700
16.66 + 5.00·105/(25000 + R )
POnAct is the active state on-hook dissipa-
tion, typically 160 mW VBat = -48V
VTRdc
=
SG · RL
where
RL + (RDC + 41700) / 600
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
ILdc = the constant loop current. ILdc is in
amperes for RDC in ohms.
from which the open loop voltage (IL = 0)
is calculated to
RDC = the programming resistance, in
ohms, which sets the constant loop
current magnitude.
5.00·105
VTRdc = 16.66 +
25000 + RSG
For RSG = open circuit, the on-hook tip
to ring dc voltage is 16.7 V, which is
compatible with VBat in the -24 V to -28 V
range.
For RSG = 0 ohm, the on-hook tip to ring
dc voltage is 36.7 V, which is compatible
with VBat in the -42 V to -58 V range.
For intermediate battery voltage values,
VBat, RSG can be calculated from
When the desired constant loop current
is known, RDC is calculated from
TJ = PShTot · (θJP + θPA) + TAmb, TJ < 140 °C
2500
where
RDC
=
- 41700
ILdc
θJP = θJP28plcc = θJP22dip is the thermal
resistance from junction to all VBAT
terminals, typically 10 °C/W θPA is the
thermal resistance from all VBAT terminals
to ambient. The θPA value will be depend-
ent on line-card thermal design.
Capacitor CDC, connected between the
RDC terminal and ground, removes noise
and vf signals from the battery feed
control loop. CDC is calculated according
to
5.00·105
RSG
=
- 25000
1
1
1
TAmb is the ambient temperature in °C.
VTRdc -16.66
CDC
=
·
+
2π · fDC
41700 RDC
Loop Monitoring Functions
where
where
fDC = 5 Hz
RSG is in ohms for VTRdc in volts
Overview
VTRdc is the open loop tip to ring
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.
voltage.Let VTRdc = |VBat| - 8 V to allow
distortion free transmission of a 3.1 Vpk 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.
RDC = constant current programming
resistance in ohms
CDC = filter capacitor in farads
Case 2: SLIC in the Active State
VTRdc > VSGRef
In the active state C1 = 0 and C2 = 1.
When the tip to ring dc voltage
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
approaches the VBat 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,
VSGref. This leaves a sufficient voltage
margin to the VBat 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.
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.
VBat - 3 V
ILdc
≈
RL + 1800 Ω
where
ILdc
= loop current
The tip to ring voltage at which the
RL
= loop resistance
4-13
ERICSSON [ ERICSSON ]
