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TVS Diode Application Note
PROTECTION PRODUCTS
Transient Protection of MOSFETS
One of the most common causes of failure in MOSFET
devices results from exceeding the maximum drain -
source voltage (V
DS
). Inductive load switching for
example can cause transients which can force V
DS
to
exceed the maximum breakdown voltage of the
MOSFET. If the transient contains enough energy, the
MOSFET will be destroyed if it begins to avalanche.
Drain-Source Protection
One method of protecting the MOSFET is to connect a
TVS diode from drain to source. To choose the correct
TVS diode, use the following guidelines:
l
The working voltage of the TVS diode (Vrwm) must
exceed the worst case supply voltage.
l
l
SI96-13
For switching inductive oads and power supply
applications, a 1500W (tp = 10/1000ms) TVS is
recommended.
Gate-Source Protection
Transient on the input of the MOSFET can puncture
the thin gate oxide of the device and melt the silicon.
Transients at the gate of the device are often due to
electrostatic discharge (ESD). Connecting a TVS diode
from gate to source can protect the MOSFET from
input transients. Choose a suppressor with a working
voltage which exceeds the MOSFET input voltage. For
suppression of ESD, a device rated at 300W (tp = 8/
20ms) will suffice.
A schematic diagram illustrating these protection
techniques is shown in Figure 1.
The TVS diode clamping voltage (Vc) must be less
than the minimum breakdown voltage of the
MOSFET under peak pulse current conditions.
SUPPLY/LOAD
DRAIN
INPUT
GATE
SOURCE
Figure 1 - MOSFET Protection
Revision 9/2000
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