## Maximum Pin Voltage that an AVR can withstand?

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Let us assume that the device is in off state(No VCC) on the PCB.

How much voltage can be applied on the devices' pin?

ATMEL--Heart Beat
Nothing Impossible

That info is in the data sheet

Tom Pappano
Tulsa, Oklahoma

It says "You should never go below -0,5 volts and never above Vcc+o.5v on any I/Oport"

But this is when the device is ON. But i am asking when the device is in OFF state.

ATMEL--Heart Beat
Nothing Impossible

To be clear, when the Vcc is 5V the tolerance is 10% so that -0.5 or +0.5 with respect to VCC it can vary.

If VCC=0 can I apply 5V on the pins? won't is damage the clamping diode of each pins?

ATMEL--Heart Beat
Nothing Impossible

If the device isn't powered, Vcc = 0, so the maximum voltage is 0.5V. That makes sense, given that the inputs are protected with diodes.

Leon Heller G1HSM

So this means that before removing the VCC I must have some protection to ALL I/O pins from external circuitry which might run under Uninterrupted Power Supplies.

This will be very difficult, is there any easy solution than putting a UPS for my AVR? :)

ATMEL--Heart Beat
Nothing Impossible

In the IBIS file it is mentioned that

Quote:

Model_type I/O
Polarity Non-Inverting
Enable Active-High
Vinl = 0.60V
Vinh = 1.40V
Vmeas = 1.00V
Cref = 50.00pF
C_comp 4.21pF 4.21pF 4.61pF
|
|
[Temperature Range] 27.00 0.12k -55.00
[Voltage Range] 2.00V 1.80V 2.20V
[Pulldown]

Can I take that when the device is in OFF state the Voltage range that could be applied is 0.6-1.4 V on any I/O pins?

ATMEL--Heart Beat
Nothing Impossible

To summaries:
1) What is the easiest way to protect my AVR from various external circuits that may give 5V on IO pins when there is no VCC.

2) Can I take this value of 0.6V and 1.40V as the maximum range or should I take -0.5 to +0.5 V?

ATMEL--Heart Beat
Nothing Impossible

Those are logic thresholds, nothing to do with maximum input voltages.

Leon Heller G1HSM

1) What is the easiest way to protect my AVR from various external circuits that may give 5V on IO pins when there is no VCC.

ATMEL--Heart Beat
Nothing Impossible

Apply Schottky diodes from each externally connected pin to Vcc. This will take the burden from the internal diodes, and keep the part from being damaged. This situation is why open collector drivers are used on logic lines connecting separate systems. Obviously, external 5v signals are going to attempt to power up your Avr when it should be "off", and this can even be a safety issue.

Tom Pappano
Tulsa, Oklahoma

Limit the current, power the AVR or isolate the AVR pins (e.g. with FETs). But strange that a self-proclaimed AVR guru needs to ask this.

Stealing Proteus doesn't make you an engineer.

Yeah, a Guru is like, supposed to know a lot of "stuff" 8-)

Tom Pappano
Tulsa, Oklahoma

Perhaps he's really a guru for something else, as shown by his avatar. I think that's a Hindi word, as well; it means an incarnation.

Leon Heller G1HSM

If your input are higher than ~0.5V then the chip will start to run off the power fed by the inputs. It is likely to run like a drunk person but it will.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

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