HC5515 Datasheet, PDF (13/17 Pages) Intersil Corporation – ITU CO/PABX SLIC with Low Power Standby

HC5515
Ringing State (C1 = 1, C2 = 0)
The ring relay driver and the ring trip detector are activated.
Both the tip and ring line drive amplifiers are powered down.
Both tip and ring are disconnected from the line via the
external ring relay.
Standby State (C1 = 1, C2 = 1)
Both the tip and ring line drive amplifiers are powered down.
Internal resistors are connected between tip to ground and ring
to V_BAT to allow loop current detect in an off-hook condition.
The loop current and ground key detectors are both active, E0
determines if the detector is gated to the DET output.
AC Transmission Circuit Stability
To ensure stability of the AC transmission feedback loop two
compensation capacitors C_TC and C_RC are required.
Figure 20 (Application Circuit) illustrates their use.
Recommended value is 2200pF.
AC-DC Separation Capacitor, C_HP
The high pass filter capacitor connected between pins HPT
and HPR provides the separation between circuits sensing
tip to ring DC conditions and circuits processing AC signals.
A 10nf C_HP will position the low end frequency response
3dB break point at 48Hz. Where:
f_3dB = ₍---₂-----_•----_π-----_•----_R-----¹_H----_P-----_•----_C-----_H----_P----₎
(EQ. 28)
where R_HP = 330kΩ.
Thermal Shutdown Protection
The HC5515’s thermal shutdown protection is invoked if a
fault condition on the tip or ring causes the temperature of
the die to exceed 160^oC. If this happens, the SLIC goes into
a high impedance state and will remain there until the
temperature of the die cools down by about 20^oC. The SLIC
will return back to its normal operating mode, providing the
fault condition has been removed.
Surge Voltage Protection
The HC5515 must be protected against surge voltages and
power crosses. Refer to “Maximum Ratings” TIPX and
RINGX terminals for maximum allowable transient tip and
ring voltages. The protection circuit shown in Figure 20
utilizes diodes together with a clamping device to protect tip
and ring against high voltage transients.
Positive transients on tip or ring are clamped to within a
couple of volts above ground via diodes D₁ and D₂. Under
normal operating conditions D₁ and D₂ are reverse biased
and out of the circuit.
Negative transients on tip and ring are clamped to within a
couple of volts below ground via diodes D₃ and D₄ with the
help of a Surgector. The Surgector is required to block
conduction through diodes D₃ and D₄ under normal
operating conditions and allows negative surges to be
returned to system ground.
The fuse resistors (R_F) serve a dual purpose of being
nondestructive power dissipaters during surge and fuses
when the line in exposed to a power cross.
Power-Up Sequence
The HC5515 has no required power-up sequence. This is a
result of the Dielectrically Isolated (DI) process used in the
fabrication of the part. By using the DI process, care is no
longer required to insure that the substrate be kept at the
most negative potential as with junction isolated ICs.
Printed Circuit Board Layout
Care in the printed circuit board layout is essential for proper
operation. All connections to the RSN pin should be made as
close to the device pin as possible, to limit the interference
that might be injected into the RSN terminal. It is good
practice to surround the RSN pin with a ground plane.
The analog and digital grounds should be tied together at
the device.
SLIC Operating States
TABLE 1. LOGIC TRUTH TABLE
E0
C1
C2
SLIC OPERATING STATE
ACTIVE DETECTOR
0
0
0
Open Circuit
No Active Detector
0
0
1
Active
Loop Current Detector
0
1
0
Ringing
Ring Trip Detector
0
1
1
Standby
Loop Current Detector
DET OUTPUT
Logic Level High
Loop Current Status
Ring Trip Status
Loop Current Status
1
0
0
Open Circuit
1
0
1
Active
1
1
0
Ringing
1
1
1
Standby
No Active Detector
Loop Current Detector
Ring Trip Detector
Loop Current Detector
Logic Level High
67