Diode Burnout
Any Schottky junction, be it an RF diode or the gate of a
MESFET, is relatively delicate and can be burned out with
excessive RF power. Many crystal video receivers used
in RFID (tag) applications find themselves in poorly con‑
trolled environments where high power sources may
be present. Examples are the areas around airport and
FAA radars, nearby ham radio operators, the vicinity of a
broadcast band transmitter, etc. In such environments,
the Schottky diodes of the receiver can be protected by a
device known as a limiter diode.
[5]
Formerly available only
in radar warning receivers and other high cost electronic
warfare applications, these diodes have been adapted to
commercial and consumer circuits.
Avago offers a complete line of surface mountable PIN
limiter diodes. Most notably, our HSMP‑4820 (SOT‑23) can
act as a very fast (nanosecond) power‑sensitive switch
when placed between the antenna and the Schottky di‑
ode, shorting out the RF circuit temporarily and reflecting
the excessive RF energy back out the antenna.
[5] Avago Application Note 1050, “Low Cost, Surface Mount Power
Limiters.”
Assembly Instructions
SOT-3x3 PCB Footprint
Recommended PCB pad layouts for the miniature SOT‑
3x3 (SC‑70) packages are shown in Figures 26 and 27 (di‑
mensions are in inches). These layouts provide ample al‑
lowance for package placement by automated assembly
equipment without adding parasitics that could impair
the performance.
0.026
0.079
0.039
0.022
Dimensions in inches
Figure 26. Recommended PCB Pad Layout for Avago’s SC70 3L/SOT-323 Products.
0.026
0.079
0.039
0.018
Dimensions in inches
Figure 27. Recommended PCB Pad Layout for Avago's SC70 6L/SOT-363 Products.
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AVAGO [ AVAGO TECHNOLOGIES LIMITED ]
