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W671300 SERIES
7.2.4.3. Logic Control
Ringing patterns consist of silent intervals. The ringing to silent pattern is called the ringing cadence.
During the silent portion of ringing, the device can be programmed to any other operating mode. The
most likely candidates are Low Power Standby or Forward Active. Depending on system
requirements, the low or high battery may be selected.
Loop supervision is provided with the Ring Trip Detector. The Ring Trip Detector senses the change in
loop current when the phone is taken off hook. The loop detector full wave rectifies the ringing current,
which is then filtered with external components RRT and CRT. The resistor RRT sets the trip threshold
and the capacitor CRT sets the trip response time. Most applications will require a trip response time of
less than 150ms.
Three very distinct actions occur when the device detects a Ring Trip. First, the DET output is
latched LOW. The latching mechanism eliminates the need for software filtering of the detector output.
The latch is cleared when the operating mode is changed externally. Second, the VRS input is
disabled, removing the ring signal from the line. Third, the device is internally forced to the Forward
Active mode.
7.2.4.4. Power Dissipation
The power dissipation during ringing is dictated by the load driving requirements and the ringing
waveform. The key to valid power calculations is the correct definition of average and RMS currents.
The average current defines the high battery supply current. The RMS current defines the load
current.
The cadence provides a time averaging reduction in the peak power. The total power dissipation
consists of the ringing power, Pr, and the silent interval power, Ps.
PRNG Pr
tr
tr ts
+
--------------
×
Ps
ts
tr ts
+
--------------
×
+
=
(EQ. 57)
The terms tR and tS represent the cadence where tR is the ringing interval and tS the silent interval. The
typical cadence ratio tR : tS is 1 : 2.
The quiescent power of the device in the Ringing mode is defined as follows.
Pr Q
( )
VBH IBHQ
×
VBL IBLQ
×
VCC ICCQ
×
+
=
(EQ. 58)
The total power during the ringing interval is the sum of the quiescent power and loading power:
Pr
Pr Q
( )
VBH IAVG
×
VRMS
2
ZREN RLOOP
+
------------------------------------------
+
=
(EQ. 59)
For sinusoidal waveforms, the average current, IAVG, is defined as follows.
IAVG
2
π
---
VRMS
2
×
ZREN RLOOP
+
------------------------------------------
=
(EQ. 60)
The silent interval power dissipation will be determined by the quiescent power of the selected
Publication Release Date: March 2004
- 29 -
Revision 0.5