CPC75282KA datasheet(15/19 Pages) IXYS

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PRELIMINARY

INTEGRATED CIRCUITS DIVISION

CPC75282

R00E

PRELIMINARY

sinking the TSDx pull up bias current to ground during

normal operation when the All-Off state is not

required. If TSDx is set to a logic 1 or tied to VCC, the

channel just ignores this input, and still enters the

thermal shutdown state at high temperature.

2.6 Ringing Switch Zero-Cross Current Turn Off

After the application of a logic input to turn SW4 off,

the ringing switch is designed to delay the change in

state until the next zero-crossing. Once on, the switch

requires a zero-current cross to turn off, and therefore

should not be used to switch a pure DC signal. The

switch will remain in the on state no matter the logic

input until the next zero crossing. These switching

characteristics will reduce and possibly eliminate

overall system impulse noise normally associated with

ringing switches. See IXYS Integrated Circuits

Division’s application note, AN-144, Impulse Noise

Benefits of Line Card Access Switches, for more

information. The attributes of ringing switch, SW4,

may make it possible to eliminate the need for a

zero-cross switching scheme. A minimum impedance

of 300

 in series with the ringing generator is

recommended.

2.7 Power Supplies

Both a +5V supply and battery voltage are connected

to the CPC75282. Switch state control is powered

exclusively by the +5V supply. As a result, the

CPC75282 exhibits extremely low power consumption

during active and idle states. Although battery power

is not used for switch control, it is required to supply

current during negative overvoltage fault conditions at

tip and ring.

2.8 Battery Voltage Monitor

The CPC75282 also uses the VBAT voltage to monitor

battery voltage. If system battery voltage is lost, both

channels of the CPC75282 immediately enter the

All-Off state. It remains in this state until the battery

voltage is restored. The device also enters the All-Off

state if the battery voltage rises more positive than

about –10V with respect to ground and remains in the

All-Off state until the battery voltage drops below

approximately –15V with respect to ground. This

battery monitor feature draws a small current from the

battery (less than 1

A typical) and will add slightly to

the device’s overall power dissipation.

2.9 Protection

2.9.1 Diode Bridge

Both channels of the CPC75282 use a combination of

current limited break switches, a diode bridge, and a

thermal shutdown mechanism to protect the SLIC

device or other associated circuitry from damage

during line transient events, such as lightning. During

a positive transient condition, the fault current is

conducted through the diode bridge to ground via

FGND. Voltage is clamped to a diode drop above

ground. Negative lightning is directed to battery via

steering diodes in the diode bridge. For power

induction or power-cross fault conditions, the positive

cycle of the transient is clamped to a diode drop above

ground and the fault current directed to ground. The

negative cycle of the transient is steered to battery.

Fault currents are limited by the current-limit circuit.

2.9.2 Current Limiting function

If a lightning strike transient occurs when the device is

in the Idle/Talk state, the current is passed along the

line to the integrated protection circuitry, and restricted

by the dynamic current limit response of the active

switches. During the Idle/Talk state, when a 1000V

10x1000

 s lightning pulse (GR-1089-CORE

lightning) is applied to the line though a properly

clamped external protector, the current seen at TLINE

and RLINE will be a pulse with a typical magnitude of

2.5A and a duration less than 0.5

s.

If a power-cross fault occurs with the device in the

Idle/Talk state, the current is passed though break

switches, SW1 and SW2, on to the integrated

protection circuit, but is limited by the DC current limit

response of the two break switches. The DC current

limit is dependent on the switch differential voltage, as

shown in “Figure 2: Switches 1-3” on page 17.

Note that the current limit circuitry has a negative

temperature coefficient. As a result, if the device is

subjected to extended heating due to a power cross

fault condition, the measured current at TLINE and

RLINE will decrease as the device temperature

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