Functional Description
Protection Circuit for Transmitter
20-40 Ω
SX1
1.8 V
VDD
S0 Bus
GND
20-40 Ω
SX2
ITS05641
Figure 47
External Circuitry for Transmitters
Figure 47 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 VDD + 0.4 V.
Via the two resistors (typ. 33 Ω) the transmitted pulse amplitude is adjusted to comply with the
requirements. Two mutually reversed diode paths protect the device against positive or
negative overvoltages on both lines.
In figure 47 the pin voltage range is increased from – 1.4 V to VDD + 2.5 V. The resulting
forward voltage of 2.5 V will prevent the protection circuit to become active if the 96 kHz test
signal is applied while no supply voltage is present. Alternatively to the 1.8 V Zener diode in
the V path two to three standard diodes connected in series achieve the same effect.
DD
Semiconductor Group
86
INFINEON [ Infineon ]
