HC5526 datasheet(15/19 Pages) RENESAS

15 / 19 page

HC5526

FN4151 Rev 8.00

Page 15 of 19

August 2003

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 VBAT +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

VBAT 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 CTC and CRC are required.

Figure 21 (Application Circuit) illustrates their use.

Recommended value is 2200pF.

AC-DC Separation Capacitor, CHP

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 CHP will position the low end frequency response 3dB

break point at 48Hz. Where:

where RHP = 330k.

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 160oC. 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 20oC. 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 (RF) serve a dual purpose of being

nondestructive power dissipaters during surge and fuses when

the line in exposed to a power cross.

FIGURE 20A.

FIGURE 20B.

FIGURE 20. LONGITUDINAL IMPEDANCE NETWORK

TIP

RING

VBAT/2

I1

I2

RLARGE

VT

ILONG

HC5526

ILONG

VR+

VBAT/2

RLARGE

TIP

RING



2I0

I1

TIP CURRENT SOURCE

WITH DIFFERENTIAL INPUTS

TIP DIFFERENTIAL

TRANSCONDUCTANCE

AMPLIFIER

f3dB





RHP



CHP





-----------------------------------------------------

(EQ. 28)

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