HC5513_03 INTERSIL [Intersil Corporation], HC5513_03 Datasheet - Page 12

• Manufacturer Part Number: HC5513_03
• Description: TR909 DLC/FLC SLIC with Low Power Standby
• Manufacturer: INTERSIL [Intersil Corporation]

A filter capacitor (C
accuracy of the trip point in a noisy environment. The value
of this capacitor is calculated using the following Equation:
Where: T = 0.5ms.
Ground Key Detector
A simplified schematic of the ground key detector is shown in
Figure 18. Ground key, is the process in which the ring terminal
is shorted to ground for the purpose of signaling an Operator or
seizing a phone line (between the Central Office and a Private
Branch Exchange). The Ground Key detector is activated when
unequal current flow through resistors R1 and R2. This results
in a current (IGK) out of the transconductance amplifier (gm2)
that is equal to the product of gm2 and the differential (ITIP -
IRING) loop current. If IGK is less than the internal current
source (I1), then diode D1 is on and the output of the ground
key comparator is low. If IGK is greater than the internal current
source (I1), then diode D2 is on and the output of the ground
key comparator is high. With the output of the ground key
comparator high, and the logic configured for ground key detect,
the DET pin goes low. The ground key detector has a built in
hysteresis of typically 5mA between its trigger and reset values.
Ring Trip Detector
Ring trip detection is accomplished with the internal ring trip
comparator and the external circuitry shown in Figure 19. The
process of ring trip is initiated when the logic input pins are in the
following states: E0 = 0, E1 = 1/0, C1 = 1 and C2 = 0. This logic
condition connects the ring trip comparator to the DET output,
and causes the Ringrly pin to energize the ring relay. The ring
relay connects the tip and ring of the phone to the external
circuitry in Figure 19. When the phone is on-hook the DT pin is
more positive than the DR pin and the DET output is high. For
off-hook conditions DR is more positive than DT and DET goes
low. When DET goes low, indicating that the phone has gone
C
D
I
I
METALLIC
METALLIC
CASE 1
=
Æ
------- -
R
¨
T
D
I
I
LONGITUDINAL
LONGITUDINAL
CASE 2
D
¨
¨
) in parallel with R
I
I
LONGITUDINAL
LONGITUDINAL
12
CASE 3
Æ
Æ
FIGURE 18. LOOP CURRENT AND GROUND KEY DETECTORS
RING
TIP
D
will improve the
HC5513
R
R
1
2
(EQ. 27)
+
+
-
-
HC5513
GROUND
KEY
COMPARATOR
gm
gm
R
off-hook, the SLIC is commanded by the logic inputs to go into
the active state. In the active state, tip and ring are once again
connected to the phone and normal operation ensues.
Figure 19 illustrates battery backed unbalanced ring injected
ringing. For tip injected ringing just reverse the leads to the
phone. The ringing source could also be balanced.
NOTE: The DET output will toggle at 20Hz because the DT input is
not completely filtered by C
and determine if the DET pin is low for more that half the time, if so
the off-hook condition is indicated.
Longitudinal Impedance
The feedback loop described in Figure 20(A, B) realizes the
desired longitudinal impedances from tip to ground and from
ring to ground. Nominal longitudinal impedance is resistive
and in the order of 22Ω.
In the presence of longitudinal currents this circuit attenuates
the voltages that would otherwise appear at the tip and ring
terminals, to levels well within the common mode range of
the SLIC. In fact, longitudinal currents may exceed the
programmed DC loop current without disturbing the SLIC’s
VF transmission capabilities.
FIGURE 19. RING TRIP CIRCUIT FOR BATTERY BACKED RINGING
H
1
2
+
-
COMPARATOR
gm
gm
1
(I
D
DIGITAL MULTIPLEXER
CURRENT
R
I
GK
METALLIC
1
RELAY
2
RT
RING
(I
TIP
LOOP
RING
TIP
- I
I
D
RING
1
R
)
2
3
C
E
RT
RG
RT
)
R
. Software can examine the duty cycle
4
V
RINGRLY
BAT
R
R
R
H
+
-
1
2
+
1.25V
V
DR
DT
REF
-
COMPARATOR
RING TRIP
+
-
HC5513
R
DET
I
RD
D
-5V
R
V
EE
D
C
DET
D