CLP270M datasheet(6/24 Pages) STMICROELECTRONICS

6 / 24 page

CLP270M

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up to 4 fixed external voltage reference (VZ1 to VZ4) (see fig. 5a, here-below).

external reference supplies, Vb1 and Vb2 (see fig. 5b, on next page).

2.4. Speech mode

In speech mode (Ring relay in position 1), the protection is provided by the combination of both CLP270M

and the external voltage reference device.

In normal conditions, the working point of this circuit is located in region 4 of A2 curve : the CLP270M is idle.

When a surge occurs on the line, the external voltage reference device clamps at GND or -Vbat respectively

for positive and negative surges.

This generates a current which is detected by Rsense and causes the protection to act : the line is

short-circuited to GND.

RINGS

Rsense

Overvoltage

reference

(+/- 270 V)

Overvoltage

detector

Overcurrent

detector

Overvoltage

reference

(+/- 270 V)

Overvoltage

detector

Overcurrent

detector

TIPL

TIPS

RINGL

GND

SW3 SW1

SW4 SW2

Rsense

Fuse

TIP

RING

VB1

VB2

Fig. 5b: Method to adjust the reference voltage.

Rsense

Overvoltage

reference

(+/- 270 V)

Overvoltage

detector

Overcurrent

detector

TIPL

TIPS

SW3 SW1

Fuse

TIP

GND

-Vbat

External

voltage

reference

ILG

VLG

ILG

VREF1

-VREF2

Fig. 6: Switching by current during speech mode.

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