PBL 3764A/4, /6
control input conditions and sets up the
commanded operating state.
In the Stand-by State the line drive
amplifiers are disconnected. The loop
feed is converted to resistive form
according to:
the DET output, which is a collector
output with internal pull-up resistor
(approx. 15 kΩ). A DET output at logic
level low indicates triggered detector
condition (loop current above threshold
current, ground key depressed or
telephone off-hook during the ringing
cycle). A DET output at logic level high
indicates a non triggered detector
condition.
Open Circuit State (C1, C2 = 0, 0)
In the Open Circuit State the TIPX and
RINGX line drive amplifiers as well as
other circuit blocks are powered down.
This causes the SLIC to present a high
impedance to the line. Power dissipation
is at a minimum. No detectors are active.
VBat -3 V
IL ≈
RL + 1800 Ω
where:
IL
= loop current (A)
VBat
= battery supply voltage (V)
E0, when set to logic level high,
disables the DET output; i.e. it appears as
a resistor connected to VCC.
E1, when set to logic level low, gates
the ground key detector to the DET
output.
E1, when set to logic level high, gates
the loop detector to the DET output.
Table 1 summarizes the above
description of the enable inputs.
RL
= loop resistance (Ω)
Ringing State (C1, C2 = 1, 0)
The standby short circuit loop current
(ILSh) for VBat = -28V is then limited to:
The ring relay driver and the ring trip
detector are activated. TIPX and RINGX
are in the high impedance state and
ILSh ≈ 13.9 mA.
Both the loop current and ground key
Active State (C1, C2 = 0, 1)
detectors are activated in this operating
state. Inputs E0 and E1 control the
selection of one of these detectors to be
gated to the DET output. Please, refer to
section “Enable Inputs”.
TIPX is the terminal closest to ground and
sources loop current while RINGX is the
more negative terminal and sinks loop
current. Vf signal transmission is normal.
Both the loop current and the ground key
detectors are activated. Inputs E0 and E1
control the selection of one of these
Table 1 summarizes the above
description of the control inputs.
Overvoltage Protection
The PBL 3764/A4 SLIC must be protected
against overvoltages on the telephone
line caused by lightning, ac power contact
and induction. Refer to Maximum Ratings,
TIPX and RINGX terminals, for maximum
allowable continuous and transient
voltages that may be applied to the SLIC.
The circuit shown in figure 12 utilizes
series resistors together with a
Enable Inputs (E0, E1)
detectors to be gated to the DET output.
Please, refer to section Enable Inputs.
Two TTL compatible enable inputs E0
(pin 13) and E1 (pin 12) control the
function of the DET (pin 14) output.
E0, when set to logic level low, enables
Stand-By State (C1, C2 = 1, 1)
Signal transmission is inhibited.
State
E0
E1
C1
C2
SLIC operating state
Active detector
DET Output
programmable overvoltage protector (e g
Texas Instrument TISP PBL2), serving as
a secondary protection.
The protection network in figure 12 is
designed to meet requirements in ITU-T
K20, Table 1.
1
2
3
4
0
0
0
0
0
0
0
0
0
0
1
1
0
1
0
1
Open circuit
Active
No active detector
Ground key detector
Ring trip detector
Logic level high
Ground key status
Ring trip status
Ringing
Stand-by
Ground key detector
Ground key status
The TISP PBL2 is a dual forward-
conducting buffered p-gate overvoltage
protector. The protector gate references
the protection (clamping) voltage to
negative supply voltage (i e the battery
voltage,VBat ). As the protection voltage
will track the negative supply voltage the
overvoltage stress on the SLIC is
minimized.
Positive overvoltages are clamped to
ground by an internal diode. Negative
overvoltages are initially clamped close to
the SLIC negative supply rail voltage. If
sufficient current is available from the
overvoltage, then the protector will
crowbar into a low voltage on-state
condition, clamping the overvoltage close
to ground.
5
6
7
8
0
0
0
0
1
1
1
1
0
0
1
1
0
1
0
1
Open circuit
Active
No active detector
Loop current detector
Ring trip detector
Logic level high
Loop current status
Ring trip status
Ringing
Stand-by
Loop current detector
Loop current status
9
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Open circuit
Active
10
11
12
13
14
15
16
Ringing
Stand-by
Open circuit
Active
Note 1
Logic level high
Note 1
Ringing
Stand-by
Table 1. SLIC operating states
Note 1 For operating states 9-16 active detectors are as for operating states 1-8. The
DET output is, however, disabled and remains at logic level high regardless of
detector status.
A gate decoupling capacitor, CTISP is
needed to carry enough charge to supply
a high enough current to quickly turn on
the thyristor in the protector. Without the
capacitor even the low inductance in the
Note 2 For operating states 1- 8 the DET output is enabled and will report the status
of the active detector. Logic level low indicates a triggered detector.
17
ERICSSON [ ERICSSON ]
