HC5526 Datasheet, PDF (13/18 Pages) Intersil Corporation – ITU CO/PABX SLIC with Low Power Standby

HC5526
I_{LONG ILONG}
TIP
+
∆V_T-
R_LARGE
I_T
∆I₁
∆I₁
G_T
I_LONG
I_LONG
∆V_R⁺
-
V_C ⁺
-
R_LARGE
RING
HC5526
∆I₂
I_R
V_BAT/2
G_R
∆I₂
TIP
R_LARGE
V_C
R_LARGE
RING
TIP CURRENT SOURCE
WITH DIFFERENTIAL INPUTS
20Ω
5kΩ ^5kΩ
-
+
∆I₁
∆I₁
V_BAT/2
2I₀
G_T
TIP DIFFERENTIAL
TRANSCONDUCTANCE
AMPLIFIER
FIGURE 20A.
FIGURE 20. LONGITUDINAL IMPEDANCE NETWORK
FIGURE 20B.
Active State (C1 = 0, C2 = 1)
The tip output is capable of sourcing loop current and for
open circuit conditions is about -4V from ground. The ring
output is capable of sinking loop current and for open circuit
conditions is about V_BAT +4V. VF signal transmission is
normal. The loop current and ground key detectors are both
active, E0 and E1 determine which detector is gated to the
DET output.
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
and E1 determine which 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 21 (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----₎
where R_HP = 330kΩ.
(EQ. 28)
Thermal Shutdown Protection
The HC5526’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 HC5526 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 21
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.
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