Exceeding Absolute maximum ratings of an IC

[FreshmanNewbie]

I have an IC, whose input GPIO 's absolute maximum rating is Vcc+0.5V.

In a scenario, I will not be giving power (Vcc) to the IC. But the GPIO will be having 3.3V as the input.
In this case, would the IC or the IC pin will be damaged? Since, Vcc + 0.5V = 0V+0.5V = 0.5V. But the pin is having 3.3V.

Since, 3.3V is greater than 0.5V, my IC pin will get damaged ?

From my understanding, the main objective of giving the absolute maximum rating as Vcc+0.5V, is to not damage the internal ESD clamping diode that is internal to the pin. So, I am thinking like, it doesn't matter if we exceed the absolute maximum rating input of the pin, but we need to make sure that the current into the pin is very small so that the diode isn't damaged. But there's no current limit mentioned for the pin. Am I correct?

So, I am confused.

To summarize my questions:

1. Why is absolute maximum rating given only in terms of voltage and not current?
2.
In a scenario, I will not be giving power (Vcc) to the IC. But the GPIO will be having 3.3V as the input.
In this case, would the IC or the IC pin will be damaged? Since, Vcc + 0.5V = 0V+0.5V = 0.5V. But the pin is having 3.3V.

Since, 3.3V is greater than 0.5V, my IC pin will get damaged ?

 

[KlausST]

Hi,

1) often the current is meantioned, too. We can not validate this in your case, because you hide the type/datasheet in secret.
2) You are correct. IC is likely to get killed.

****
You also hide the circuit as a secret. So we have to guess.
So if the pin is an input, then usually it is very high impedance. So a series resistor of let´s say 10k won´t hurt. Then add a BAT54S (A = GND, K = VCC, AK = pin) and you are safe.

There are many other solutions. Some may work for your application, some may not. We just don´t know your true requirements.

Klaus

 

[betwixt]

adding to Klaus's explanation:

1. the absolute maximum is usually quoted under a normal circuit connection configuration, exceeding it is likely to cause rupture in an insulation barrier inside the device or cause overheating if V*I becomes excessive for some part of the device.

2. Most ICs have some kind of internal ESD clamping between signal/data pins and their VSS/VDD pins. If VDD is removed, the ESD diode will conduct current from the signal/data pin either to ground or VDD. In the scenario you posted, putting 3.3V on a signal/data pin will try to raise the VDD line voltage to about 2.7V (3.3 - ESD diode Vf). What we cannot tell is whether that is safe or not. Most likely the IC itself will try to partially power up and may misbehave but if the VDD pin also connects to other devices it will try to power those up as well and if sufficient current can come from the signal/data pin it will probably destroy the ESD diode. There is also a danger of latch-up if the ESD diode is conducting and normal VDD is reapplied, whether this will happen depends on the type of IC and it's input circuitry.

Brian.

 

[danadakk]

A good discussion of latchup :

https://www.ti.com/lit/wp/scaa124/scaa124.pdf

Regards, Dana.

 

[D.A.(Tony)Stewart]

ESD diodes have small current limits (<1 mA) in order to be small enough to be faster than the FET it is protecting. Thus protection from 4kV may have 10k ohm

imagine that if you pull up the I/O thru the ESD diode, you are also charging up the low-ESR cap on Vdd:Vss.

So understand if you may be burning out your protection diodes or not. there are usually 2 stages of R-D protection so if Vdd is 0V, then ok.

 

[FvM]

As stated, maximum current through ESD diodes is often specified. E.g. STM32 specifies +/- 5 mA "injected current" maximum. Need to provide respective series resistors or similar protection means.

 

[dick_freebird]

The pin current spec is for powered operation, latchup trigger.
Pin voltage is meant to enforce that you never forward-bias
the ESD diodes, so that current should never appear in VDD
(VDD+0.5) or VSS (-0.5V).

Abs Max ratings are only the manufacturer's limitation of
responsibility for field failures. They inform you of nearly
nothing (and IME often are just "reused boilerplate" with no
effort to see what the part and pin can really stand, for how
long). Just try and get your boss to approve you taking two
weeks of lab time to enable customers to more fully abuse
the product (getting right up against whatever they were
violating) at company expense & risk.

You don't get to know "why?" or "how close?". That would
take vendor effort and expose the vendor to the next layer
of the questions-onion which is always picker, trickier and
wider. And then you'll step over -that- line and come whining
for a Mulligan, after they went and shaved the safety margin
already.

 

[KlausST]

The pin current spec is for powered operation, latchup trigger.

Example: ATMEGA328P datasheet specifies:

Injection current at VCC= 0V: ±5.0 mA

A see "VCC = 0V" as not_powered.

Klaus

 

[danadakk]

328p data sheet injection current at VCC = 5V

Regards, Dana.

 

[D.A.(Tony)Stewart]

1st time I've noticed an Absolute Maximum spec with typical values.

I guess not all CMOS use current limiting resistors with the ESD diodes with 2 stages, as I suggested before. But then, I was thinking of inputs only.
I/O ports might be driving inductive wires and thus need Schottky rail clamps to avoid triggering the SCR effects in the substrate.

Figure from an ATtiny datasheet may be typical of all I/O ports with pin capacitance, diodes and internal pull-up options. Diodes also have maximum capacitance at 0V, but not a lot for low current types.

 

[KlausST]

Hi,

328p data sheet injection current at VCC = 5V

Obviously the datasheet specifies both, powered and unpowered.

But since the OP in post#1 asks about unpowered situation I followed his requirement on this and thus referred to the "VCC = 0V" specification.

So in other words: If the OP asks about unpowered situation, then the powered_specification does not relate.


Klaus

 

[D.A.(Tony)Stewart]

Hi,


Obviously the datasheet specifies both, powered and unpowered.

But since the OP in post#1 asks about unpowered situation I followed his requirement on this and thus referred to the "VCC = 0V" specification.

So in other words: If the OP asks about unpowered situation, then the powered_specification does not relate.


Klaus

exception

 

[KlausST]

Hi,

what do you mean? I see no exception.

Klaus