Echelon FT 3150 Smart Transceiver - Manual (Page 143)

FT 3120 / FT 3150 Smart Transceiver Data Book 137
Power Distribution and Decoupling Capacitors
• Use diodes, transient voltage suppressors (ex: MOSorbs, transorbs, ...) for high-speed clamping.
• Use capacitors to protect critical inputs.
• Use good power distribution.
• Use a separate, low-impedance ESD ground path to divert energy from electronics (ex: “star” ground strat-
egy).
NOTE: The impedance of a wire at 300MHz is approximately 20 Ω/cm. Use a conductor with less than or equal to
3:1 length:width ratio.
Recommended Reading
Total Control of the Static in Your Business
Available by writing to:
Static Control Systems Div.
Box ELB-3, 225-4S
3M Center
St. Paul, MN 55144
Or by calling:
1-800-328-1368
1-612-733-9420 (in Minnesota)
Power Distribution and Decoupling Capacitors
Inductance in the power distribution creates noise during switching transients.
Figure C.8 Inductance Creates Noise
For example, a 200nH inductor with 25mA and 5ns surge characteristic can generate 1 V in noise:
Vnoise = L dI/dt
L = 200nH, dI = 25mA, dt = 5ns
Vnoise = 200 nH * 25mA / 5ns = 1V