Reversing VCC and GND

Using Arduino General Electronics
#1

I have a little SIP breakout board with a BMP280 on it. I got tired of checking the datasheet every time I wanted to wire it up in a circuit so I made a little label for it and stuck it on the board.

Unfortunately I mislabeled it, reversing VCC and GND on the label. It obviously didn’t work when I tried it this way. But what surprised me was that it still worked when I corrected my mistake. According to the datasheet I exceed the maximum voltage (max=VCC+0.3V) on several of the pins.

Why didn’t it blow up?

#2

Why didn't it blow up?

Exceeding the recommended voltage, by a small amount, is generally not fatal. It will shorten the life of the component, by some amount.

Does your "little SIP breakout board" have diodes to protect itself?

#3

Oops. Wrong forum. I meant to put this in General Electronics.

#4

I asked that it be moved.

#5

PaulS: Exceeding the recommended voltage, by a small amount, is generally not fatal. It will shorten the life of the component, by some amount.

Does your "little SIP breakout board" have diodes to protect itself?

No, nothing on the board except the chip and two decoupling caps.

With VCC = 0V and CS, SCK and MOSI all driven to 3.3V, wouldn't that be enough to do it? I reversed VCC and GND on an OLED display one time and it was toast.

#6

With VCC = 0V

I really wouldn't even expect the device to wake up and care what voltage was on the other pins. But, it is very difficult to apply the wrong voltage to software, which is my area of expertise.

#7

Normally reversing the power leads results in a higher than normal current. If the power supply can give you enough current you melt things inside the chips. However if the power supply somehow limits the current either through over current protection or just impedance, and you don't have it connected for long then it is not always immediately fatal. Although at times it can be.

#8

There are usually clamping diodes on each input of the chip (up to 4 per input). When you reverse the supply all the diodes are forward biased so they shunt the current and helping the chip to survive. Logic chips are quite immune against reversing, any analog chips usually blow up :)

#9

Thanks, that's good to know. I wish the OLED I ruined had that safeguard.

#10