Short? Open? - Semiconductor Business -Macnica

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DesignFPGA /CPLD/ASIC Altera Corporation

One day. I am writing a training diary.

“Electricity is not something that disappears once it is used, but something that continues to flow.

If you don't connect the device or board to ground, there is no way for the current to escape, so it just keeps flowing through the conductor.

When that happens, the circuit shorts out..."

When I was typing that sentence, I got a bad review from my senior.

Senpai: “That’s because it’s not short. It’s because it’s open.”

Me: "What is Open?"

Senpai ``No electricity. Electricity doesn't flow because it's not connected.

I said, "Ah..."

A brief explanation of these two phenomena is

● Short: A state in which the power supply and ground are directly connected without any intervention.

● Open: State in which the power supply and ground are not connected

Since no current flows in an open circuit, the device or circuit will not work.

But a short circuit is a state in which the power supply and ground are connected without a resistor, so

According to Ohm's law "current = voltage ÷ 0 Ω = ∞", an infinite current is flowing.

In other words, if a large current flows into the transmission line, the power supply source may be damaged or peripheral components may be damaged.

Altera's FPGA/CPLD also has Absolute Maximum Ratings.

In a nutshell, "value that breaks when it exceeds this value".

Absolute maximum rating.

Since the absolute maximum rating value varies depending on the type of power supply, it is necessary to check each one.

These numbers vary by device family, but the table above is for Cyclone® IV.

For example, if the I/O voltage level was 3.3 V,

3.3 V is supplied by connecting VCCINT (power supply for internal core) as VCCIO (power supply for I/O).

Exceeding the absolute maximum ratings can lead to catastrophes such as destruction of the internals of the device.

When I muttered to myself that I learned something else, my senior said a few words.

"Ah, if I break both of the devices I provided for the production training, I'll have to pay for myself next time."

and left.

"...Let's check the soldering and wiring before turning on the power!"

I couldn't help but swear in my heart.

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