psf2115 ETC-unknow, psf2115 Datasheet - Page 85

• Manufacturer Part Number: psf2115
• Description: Isdn Adapter Circuit Ipac
• Manufacturer: ETC-unknow

voltage will prevent the protection circuit to become active if the 96 kHz test signal is
applied while no supply voltage is present. In TE / LT-T modes the 5.6 V zener diode is
provided to be completely on the safe side, however, system tests may reveal that it can
be omitted.
The following recommendations aim at achieving the highest possible device protection
against overvoltages while still fulfilling the 96 kHz impedance tests.
If the device is not used in TE or LT-T applications, the four diodes could be bridged and
the 5.4 V Zener diode could be omitted.
Protection Circuit for Transmitter
Figure 27
Figure 27 illustrates the secondary protection circuit recommended for the transmitter.
An ideal protection circuit should limit the voltage at the SX pins from – 0.4 V to V
+ 0.4 V.
Via the two resistors (typ. 20 ... 40 ) the transmitted pulse amplitude is adjusted to
comply with the requirements. Two mutually reversed diode paths (low capacitive diodes
are recommended, e.g. 1N4151) protect the device against positive or negative
overvoltages on both lines.
The pin voltage range is increased from – 0.7 V to V
Semiconductor Group
LT-S mode:
TE and LT-T modes:
External Circuitry for Transmitters
SX2
SX2
SX1
SX1
GND
GND
20-40
20-40
20-40
20-40
85
5.6 V
DD
+ 3.5 V. The resulting forward
V
DD
Functional Description
2 : 1
ITS10289
V
DD
S Bus
2 : 1
ITS09632
PSB 2115
PSF 2115
S Bus
11.97
DD