psb2120 Infineon Technologies Corporation, psb2120 Datasheet - Page 8

• Manufacturer Part Number: psb2120
• Description: Isdn Remote Power Controller
• Manufacturer: Infineon Technologies Corporation

Polarity Detection
Emergency conditions are signaled to the TE by the reversed polarity of the line feeding voltage.
When polarity reversal is detected via pin POL of the PSB 2120, emergency conditions are signaled
to the microprocessor via pin EME, which should shut down all activity except simple telephony
functions to minimize power dissipation.
The polarity detection circuit can also be used for other detection or protection-functions, e.g.
programmable primary undervoltage detection.
Power Housekeeping
An integrated 6 V linear voltage regulator supplies the internal circuits during the start-up phase.
Power dissipation of this regulator can be reduced, if an auxiliary winding of the transformer or an
external supply is used for that purpose by connecting it to
6.2 V the internal linear voltage regulator turns off and the internal circuits are fed from this external
voltage. In this case the input current at
Note: An internal 7.5 V Zener-diode protects the
Interface to Microprocessor
The PSB 2120 offers two TTL-compatible signals: EME and CO. The EME (Emergency-output)
becomes active, if polarity reversal is detected. CO is the output of a universal usable comparator;
e.g.: to generate a microprocessor-reset signal.
Semiconductor Group
Zener-current is 2 mA! If the external supply isn’t stabilized, the input current must be limited
(e.g. by a resistor)!
V
EXT
is approx. 0.5 mA.
8
V
EXT
input against overvoltages. The maximum
V
EXT
. If the input voltage at
PSB 2120
V
EXT
reaches