Over Voltage Protection - Texas Instruments 2000 Series Reference Manual

For applications where there is a risk that voltage spikes and noise are on the lines to the RFM, additional
protection circuitry and filters must be added. A proposal on how this may be achieved is shown in
Figure G-1, and this circuit may be used as a guideline for protection circuitry. This may not be sufficient
for all applications, however, and must be checked individually when necessary.
1. The supply input has to be protected against voltage spikes. R1 and D1 fulfil this purpose. Zener diode
D1 clamps the voltage spikes to 18 volts so that the maximum allowed transmitter power stage supply
voltage is not appreciably exceeded. For diode D1, type ZY18 is recommended, this type having a 2 W
power dissipation. If a higher current is needed, dump type ZX18 may be used, this diode having a
12.5 W power dissipation.
2. The Common Mode Choke Coil and the capacitors C1 and C2 are used to reduce the conducted noise
coming to the RFM via the supply lines.
3. All input and output signals should be protected with 5.6 V zener diodes. The specified type can dump
1.3 W.
4. The coils L1 to L6 are ferrite beads and should put in series to the line when conducted noise is
observed entering via the interface lines.
5. The varistor V1 protects the antenna circuit against high voltage induced at the antenna coil, for
example by lightning. The type of varistor given is commonly available but may not be sufficient for
protection in all cases.
Note: The zener diodes types given in
suppresser diodes for fast voltage spike suppression. If the application requires it, special
suppresser diodes should be used.
SCBU022 – November 2002
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Over Voltage Protection

Figure G-1 are commonly used types, not special
Appendix G
SCBU022 – November 2002
Over Voltage Protection 47