|
PolyDiodeTM
Electromagnetic Compatibility
Countermeasure for Transient Surge and Static Electricity
DESCRIPTION
Because electronic systems have been migrated to miniature levels in compact
size,
more and more devices require protection against ElectroStatic Discharge (ESD)
and surge, and increasingly become important.
PolyDiodes are bi-directional transient voltage suppressor devices made of
poly- crystalline mixed oxide ceramics, which offer rugged protection and excellent
electrostatic absorption and pulse noise absorption in a small package. These
devices not only require significantly smaller space than silicon TVS diodes,
but also offer greater circuit board layout flexibility for the designer.
Previously, the internal bus lines of mobile equipment and in LCD panels, key
switches, battery terminal, microphone, or headphone terminal were protected
from ESD surge by Zener diodes or silicon TVS diodes. However, unlike a Zener
diode or a TVS diode, a PolyDiode does not require being combined with an EMC
capacitor because in its off state the network acts like an EMI filter. Again,
thanks to PolyDiode possessing excellent response characteristics and ESD absorption
power, its functions are more than that of a MLV or a Zener diode and a Silicon
TVS diode.
ELECTRICAL ADVANTAGES
• Extra low clamping voltage
The PolyDiodes have an excellent clamping voltage capability (Typical ratio
of clamping voltages to breakdown voltages are between 1.25 and 1.60), that
is equal to or better than Zener diodes and Silicon TVS diodes.
The MLV’s clamping voltage is typically higher than comparable PolyDiodes
or Silicon TVS diodes. MLVs are mainly uses for ESD on less sensitive lines
where their higher clamping voltages can be tolerated.
• Low electrostatic capacity
PolyDiode exhibits a very low capacitance which can be used as an EMI/RFI
filter, adequate to support high speed signal line/ data bus use (ESD protection
for USB2.0 interfaces and ICs ), without performance distortion and/or attenuation.
The capacitance of a Zener diode or a TVS diode can be made lower by narrowing
its connection area, but a lowered wattage or a lowered ESD resistance is
unavoidable.
• Excellent ESD Endurance capability
Withstands ESD Durability test severity of IEC 61000-4-2 level 4 (8KV contact
ESD, 20 shots: 10 positive, 10 negative polarities; repetition rate 1 . sec.-1)
without damage or degradation. The electrical performance is Excellent.
• PolyDiode has the fastest response time in the industry < 0.5
ns
Poly Diode has no follow on current and their parasitic inductance is very
low, which results in response times of < 0.5 ns. Zener diode and silicon
TVS diode have a larger parasitic inductance, and the typical values of response
times are between 0.8 and 3 ns.
• Excellent surge suppression capability
PolyDiode keeps symmetrical I-V characteristics even after suppressing extremely
fast voltage transients, including electrostatic absorption and pulse noise
absorption.
The Zener diodes or TVS diodes are not sufficient for a peak surge current.
• Electrical performance in changes of temperature
The electrical characteristics of PolyDiode include operating voltage, surge
current, energy absorption and power dissipation remain unchanged up to temperature
of 85℃ of working condition. On the contrary, the TVS diodes start to deteriorate
at temperature of 25℃.
• Low leakage currents
The leakage currents less than 5 μA for PolyDiode are relatively much lower
than those of less than 100 μA for TVS diodes.
PHYSICAL ADVANTAGES
• Excellent mount reliability
The PolyDiodes electrodes are adopted Nickel/ Tin electroplating achieved
good solderability and solder heat resistance.
• Economical cost in mounting process
Since PolyDiode is bi-directional component, it is easy to mount them onto
the circuit boards. In contrast, the mounting machine must position TVS diode
with correct polarity due to their natures in unidirectional device. This
may cost higher error probability during the mounting process.
• RoHS Compatible
APPLICATIONS
• Pulse noise absorption
• Electrostatic absorption
|
