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Renesas India - Knowledgebase

Is there a problem with input voltage of -0.5V using a +5V power supply?

Latest Updated:12/01/2011


I'm using the uPC177 with a +5V single power supply, and during operation I input a pulse of about -0.5 V to the input pins.
The data sheet (Japanese) states that the absolute maximum rating of the input voltage is -0.3V to +36V.
Is there a problem with an input voltage of -0.5V ?


The absolute maximum ratings must not be exceeded, so a rating of -0.5V is not supported.
We recommend adding a protection circuit to the input.

Normally, a parasitic diode is attached to the input pins of an IC.
If a voltage higher (or lower) than the power supply (or GND) is applied to the input pins, a current will flow from the input pins to the power supply (or GND) via the parasitic diode.

The current flowing through the parasitic diode will probably not cause any damage, up to about 5mA.
However, the operation may become unstable, so it is very important that the absolute maximum ratings are not exceeded under any circumstances.

 If it is possible that a negative voltage may be applied to the input, the most common way to protect the input is by using a diode, as shown in the figure on the left.
In this case, we recommend using a Schottky barrier diode with a small forward voltage.
On the other hand, if a voltage exceeding the power supply voltage will be applied, insert a diode between the input and the power supply.

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