JUNE 2001 – REVISED FEBRUARY 2005

Specifications are subject to change without notice.

Customers should verify actual device performance in their specific applications.

TISP4xxxH3/M3BJ Series for LCAS Protection

LCAS Switch Ratings

Equivalent Circuit

Figure 13 shows the LCAS switch voltage ratings as breakdown diodes, which must not be allowed to conduct. Each switch has three diodes;

one between poles and the other two from each pole to ground. At 25 °C, switches SW1 through to SW3 have breakdown diode voltages of

±320 V. Switch SW4 has breakdown diode voltage values of ±465 V for the one between poles and ±320 V for the two diodes connected to

ground. Note that only protection to ground is required, as in the limit, the inter-switch voltage limitation of ±640 V is the same as the switch to

ground limitation of +320 V and -320 V in both polarities.

When a switch is in the off state, the maximum withstand voltage may be set by the switch itself or by the control line to the switch. At 25°C,

the switch terminal to ground voltage rating for all the switches is ±320 V. Switches SW1 to SW3 are bidirectional MOS types and can

withstand ±320 V between terminals. Switch SW4 is a bidirectional thyristor which is rated at ±465 V between terminals.

Overcurrents as well as overvoltages occur on telephone lines. In the on state, the thyristor switch, SW4, is capable of withstanding high levels

of current overload. For currents above about 200 mA, the MOS switches, SW1 to SW3, will go into a current limited condition. This will cause

the voltage to rise across the switch and large amounts of power to be developed. In the longer term, this power loss increases the overall chip

temperature. When the temperature exceeds about 125 °C, thermal shutdown occurs and the switches are set to the off state. Without power

loss, the LCAS will cool. Eventually, the thermal trip will reset, setting the switches back in the high power loss condition again. The cycle of

temperature increase, thermal shutdown, temperature decrease and switch re-activation will continue until the overcurrent ceases.

Figure 13. LCAS Shown with Switch Breakdown Limits

RING

RELAY

SLIC

RELAY

RING

GENERAT OR

SW5a

SW5b

R1

R2

V

BAT

√

√

Th1

Th2

Th3

Th4

SLIC

V

bat

RING

TIP

SW3

SW4

SW1

SW2

√

√

√

√

V

BAT

0

RING

WIRE

TIP

WIRE

V

√

√

V

√

√

V

BAT

0

RING

WIRE

TIP

WIRE

GROUND-BACKEDRINGING

SW5 AS SHOWN

BATTERY-BACKED RINGING

SW5 OPERATED

R1

R2

AI4XAR

TISP4125M3

OR

TISP4125H3

TISP4219M3

OR

TISP4219H3