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
controlled 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.
[6]
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)
or HSMP‑482B (SOT‑323) can act as a very fast (nano‑
second) power‑sensitive switch when placed between
the antenna and the Schottky diode, shorting out the
RF circuit temporarily and reflecting the excessive RF
energy back out the antenna.
Assembly Instructions
SOT-323 PCB Footprint
A recommended PCB pad layout for the miniature SOT‑
323 (SC‑70) package is shown in Figure 33 (dimensions
are in inches).
0.026
0.079
0.039
0.022
Dimensions in inches
Figure 33. Recommended PCB Pad Layout for Avago’s SC70 3L/SOT-323
Products.
A recommended PCB pad layout for the miniature
SOT‑363 (SC‑70 6 lead) package is shown in Figure 34
(dimensions are in inches). This layout provides ample
allowance for package placement by automated
assembly equipment without adding parasitics that could
impair the performance.
0.026
0.075
0.035
0.016
Figure 34. Recommended PCB Pad Layout for Avago’s SC70 6L/SOT-363
Products.
[6]
Avago Application Note 1050, Low Cost, Surface Mount Power Limiters.
13
AVAGO [ AVAGO TECHNOLOGIES LIMITED ]
