US 6,586,984 B1Granted

Method for preventing damage to IO devices due to over voltage at pin

AssigneeLSI Logic Corporation

InventorRussell E. Radke

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Abstract

A circuit which provides that a source voltage and a pad voltage are band-limited and source-followed down in order to get them into the input range of a comparator, the output of which signals an over-voltage condition on the pad. The circuit provides the ability to provide the relationship between the source voltage and pad voltage to a comparator with a very small, tightly-controlled offset. This translates to the ability to detect very small over-voltage conditions on an IO. The circuit consumes little power, is highly accurate, and requires no special, expensive process options. The circuit can be used anywhere there is a desire to compare (with a small, accurate offset) two signals that are close to a source voltage, such as VDD. The circuit can also be used to compare signals close to VSS.

Claims8

Dependent claims

A circuit configured to receive a source voltage and a pad voltage, said circuit comprising:

a first input for receiving the source voltage;
a second input for receiving the pad voltage;
at least one band-limiting resistor connected to the first input and having a resistance which provides that said at least one band-limiting resistor band-limits the source voltage;
at least one band-limiting resistor connected to the second input and having a resistance which provides that said at least one band-limiting resistor band-limits the pad voltage;
at least one source-follower transistor connected to the first input to source-follow down the source voltage;
at least one source-follower transistor connected to the second input to source-follow down the pad voltage;
a comparator which receives said source voltage and said pad voltage and compares the two to determine when an over-voltage condition exists;
and at least one resistor connected to the source-follower transistor which is connected to the second input and having a resistance which provides that an offset is introduced to said pad voltage before said pad voltage is provided to said comparator.

5 more elements

Dependencies are inferred from the claim text.