Si32172/3/5

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6. Power Monitoring and Power Fault Detection

The Si32172/3/5 line monitoring functions are used to continuously protect against excessive power conditions.

The Si32172/3/5 contains an on-chip, analog sensing diode that provides real-time temperature data and turns off

the device when a preset threshold is exceeded.

If the Si32172/3/5 detects a fault condition or overpower condition, it automatically sets that device to the open

state and generates a "power alarm" interrupt.

The interrupt can be masked, but masking the automatic transition to open is not recommended since it is used to

protect the Si3217x HVIC under excessive power conditions.The various power alarms and linefeed faults

supporting automatic intervention are described below.

1. Total power exceeded.

2. Excessive foreign current or voltage on TIP and/or RING.

3. Thermal shutdown event.

6.1. Thermal Overload Shutdown

If the die temperature exceeds the maximum junction temperature threshold, TJmax, of 145 °C or 200 °C, the

device has the ability to shut itself down to a low-power state without user intervention. The thermal shutdown

circuit contains a sufficient amount of hysteresis and/or turn-on delay time so as to remain shut down during a

power cross event, where 50 Hz or 60 Hz, 600 V, is connected to TIP and/or RING.

Table 16. Linefeed Operating States

Linefeed State

Description

Open

Output is high-impedance, and all line supervision functions are powered down. Audio is

powered down. This is the default state after powerup or following a hardware reset. This

state can also be used in the presence of line fault conditions and to generate open switch

intervals (OSIs). This state is used in line diagnostics mode as a high impedance state

during linefeed testing. A power fault condition may also force the device into the open

state.

Forward Active

Reverse Active

Linefeed circuitry and audio are active. In Forward Active state, the TIP lead is more posi-

tive than the RING lead; in Reverse Active state, the RING lead is more positive than the

TIP lead. Loop closure and ground key detect circuitry are active.

Forward OHT

Reverse OHT

Provides data transmission during an on-hook loop condition (e.g., transmitting caller ID

data between ringing bursts). Linefeed circuitry and audio are active. In Forward OHT

state, the TIP lead is more positive than the RING lead; in Reverse OHT state, the RING

lead is more positive than the TIP lead.

TIP Open

Provides an active linefeed on the RING lead and sets the TIP lead to high impedance

(>400 k

) for ground start operation in forward polarity. Loop closure and ground key

detect circuitry are active.

RING Open

Provides an active linefeed on the TIP lead and sets the RING lead to high impedance

(>400 k

) for ground start operation in reverse polarity. Loop closure and ground key

detect circuitry are active.

Ringing

Drives programmable ringing signal onto TIP and RING leads with or without dc offset.

Line Diagnostics

The channel is put into diagnostic mode. In this mode, the channel has special diagnostic

resources available.