And8350.rev0

Prepared by: Alan Ball
ON Semiconductor
http://onsemi.com
APPLICATION NOTE
Introduction
the high side or an n-channel FET can be added in the low Semiconductor’s eFuses offer low cost, low impedance solutions for bus protection and offer much N-channel FETs are more cost effective and are normally faster protection than many fuse solutions. They are an preferred if it is acceptable to break the ground line. If the effective replacement for a polyfuse and TVS clamping load has other connections to circuits that may be energized under a reverse polarity input condition, the ground should One area in which they differ in performance is reverse polarity protection. While a TVS device and polyfuse will If it is required to break the high side, a p-channel FET protect against reverse voltages, the nature of an integrated should be used. The two circuit configurations are shown in semiconductor device does not inherently allow for this type The reverse protection circuit includes a zener protection This simple circuit allows the device to protect against diode to protect against excessive gate to source voltage that reverse voltage situations by simply blocking the reverse could damage the FET. For FETs with 12 V or lower gates, voltage. This is equivalent of the action of a poly fuse only this is recommended. For FETs with 20 V gates, the zener with less leakage. In comparison to a mechanical fuse, this and resistor can be eliminated and the gate tied directly to the is a far superior solution since the mechanical fuse will not other rail as long as the maximum system transient spec is reset and this circuit will automatically reset when the A table of suggested FETs is included. The voltage and Circuit Description
DS(on) are only suggestions. The system voltage specifications should be taken into account to determine the In order to protect against reverse voltages an external maximum FET voltage and the losses due to the R switch is required. There are two basic topologies that can the FET. Please see the ON Semiconductor website accomplish this function. A p-channel FET can be added in (www.onsemi.com) for more options for FET choices.
Figure 1. High-side Protection Circuit.
Semiconductor Components Industries, LLC, 2008 November, 2008 − Rev. 0
AND8350/D
Figure 2. Low-side Protection Circuit.
Table 1. SUGGESTED FETS FOR REVERSE PROTECTION CIRCUITS
Recommended
N-Channel FETs
Recommended
P-Channel FETs
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AND8350/D

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