Datasheet

73M1866B/73M1966B Data Sheet DS_1x66B_001
74 Rev. 1.6
11.7 Voltage and Current Detection
The 73M1x66B is capable of detecting the following circumstances:
• Under voltage on the line.
• Over voltage on the line.
• Over current.
These 73M1x66B built-in mechanisms provide protection to both the device itself and the external line
circuitry.
If enabled, Over Voltage and Over Current detection will cause the 73M1x66B to go on-hook without the
intervention of the host.
If configured in Line Powered Mode, the detection of an under-voltage condition causes the 73M1x66B to
switch automatically to Barrier Powered Operation (see Section 9.2.1). This is done without the
intervention of the host.
For each of the detection functions there are enable control bits and detection status bits. For each
function there is a master detection function enable bit that must be set in order for the functions to work.
11.8 Under Voltage Detection (UVD)
Under Voltage Detection is an important feature of 73M1x66B. It determines if the phone line is not
capable of supplying the current that the 73M1x66B requires from the line for proper operation. If this
function is enabled and if the line is not capable of providing this current, the UVD condition will be
asserted and can become a source of interrupt from the 73M1x66B to its connected host.
11.9 Over Voltage Detection (OVD)
If enabled, Over Voltage Detection is indicated if the device senses that the line voltage exceeds a
defined threshold. The device allows the selection of choice of either 60 Vpk or 70 Vpk (depending upon
the attenuation ratio, typically this is 100:1).
If enabled, the 73M1x66B will automatically go on-hook if over voltage is detected.
11.10 AC Signal Overload Detection
This is the same feature as used for the detection of billing tones (see Section 10.4). In this most generic
sense, this detector provides an indicator that the AC signal on the line exceeds a value of 3.5 Vpk.
11.11 Over Current Detection (OID)
When the line current exceeds the safe operating range of the 73M1x66B or the external transistors, the
device indicates this condition. If enabled, the 73M1x66B will automatically go on-hook if an over current
event is detected.