PBL38772/1 데이터 시트보기 (PDF) - Ericsson
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PBL38772/1 Datasheet PDF : 24 Pages
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PBL 387 72
Foreign voltage protection: The control device will detect if
Tip and/or Ring are shorted to e.g. ground. The output voltage
will be shut off to keep the power down. The detector output
will be high.
Temperature management: If the chip temperature
exceeds 155 °C the control device will reduce the output
voltage until the chip temperature equals 155 °C, and
increase it again when the temperature drops. The detector
output, DET, is forced to a logic low level when the
temperature guard is active.
PBL 38772/1
+
VR
-
GND
VR
PA
Tip
IL
RING
IL
Temp.
Control
device
α
CRING PRT
PA
-
+
CRING
RRT
CRT
20 Ω TIP
IL
V TR
RL
20 Ω RING IL
DET
Figure 13. Ring loop schematic.
The VR pin is a high impedance input. The voltage VR has a
reference to AGND. This input has to have a resistor, RVR
= 200 kΩ, connected to ground, and a capacitor, CVR =
470 nF, in series to decouple the DC component. The input
handles any waveform, e.g. sinusoidal, trapezoid or square-
wave shaped signals, since the SLIC acts like a linear
amplifier. When using a square-wave input signal it has to be
filtered and therefore add a capasitor of 10 nF parallel with
the RVR resistor. A DC-offset can be obtained by adding a DC
part to the input signal. The capacitor CRING forms a low
pass filter that is an essential part of the control device. The
control is used to control e.g. the applied output voltage,
the ringing current or the chip temperature. The resistor RRT
is a programming resistor that sets the ring-trip detector
threshold. The current through the resistor is a rectified
version of the line current divided by a factor The capacitor
CRT filters the ring-trip detection device. PRT-pin is connected
to the negative input of an OP-amplifier. The positive input
is connected to a reference voltage. The output of the
OP-amplifier is connected to the detector output DET. When
the voltage over the resistor RRT exceeds the reference
voltage the detector output changes state.
The ring injection will be describes in more detail with figure
14 and 16. Figure 14 shows a ring sequence with an off-hook
at time t1. The first diagram shows the voltage applied to the
input, VR, together with the voltages at TIPX and RINGX pins.
The voltage of the TIP wire follows the voltage of the VR pin.
The second diagram shows the rectified current, IL/α through
the resistor RRT. The dotted line represent the programmed
ring-trip threshold, ILTH/α The third diagram shows the voltage
on the detector output. Before time t1, the phone supposed
to be on-hook. The ring voltage is applied symmetrically
around a fixed voltage, VBat/2, to the load. As long as the
telephone is on-hook the rectified current IL/α will not exceed
U [V]
GND
t1
VBAT/2
VBAT
IL/α [A]
ILTH/α
t1
DET [V]
t1
Figure 14. Off-hook during ringing.
VR
t [s]
RING
TIP
t [s]
t [s]
EN/LZT 146 136 R1A © Ericsson Microelectronics, December 2001
U [V]
GND
t1
VBAT/2
VR
t [s]
RING
TIP
VBAT
IL/α [A]
ILTH/α
t1
t [s]
DET [V]
t1
t [s]
Figure 15. Off-hook during Ringing with an applied DC offset.
17
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