https://www.fairchildsemi.com/an/AN/AN-9068.pdf?From that:QuoteOne of critical control parameters in gate-drive design is external series gate resistor (Rg). ... As too small Rg results in excessive dv/dt across drain and source of the MOSFET during switching-off, low limit is a value that makes switching dv/dt within the specification in the datasheets.The reference in that document to "critical control parameters" suggests to me that this is not an optional resistor.That datasheet may not necessarily be relevant to the particular MOSFETs we are testing, however I can't help hearing warning bells there when I read it.
One of critical control parameters in gate-drive design is external series gate resistor (Rg). ... As too small Rg results in excessive dv/dt across drain and source of the MOSFET during switching-off, low limit is a value that makes switching dv/dt within the specification in the datasheets.
whatever information you do have is based on what? Speculation? Hearsay?
... some particular chip samples and a whole lot of speculation.
Maybe the "250mA" figure that you so eagerly dismiss was for a chip from an older production process.
Quote from: fungus on Jul 14, 2013, 03:00 pm... some particular chip samples and a whole lot of speculation.Actually doing tests is speculation? Hmmm...
4) How do you deal with parameters that are not in datasheets?
The famous "pin output voltage drop vs. current" graphs only go up to 20mA. Beyond that, it's 100% pure speculation, yes.
Maybe they're left out for a reason, ie. to allow them to change their production processes without breaking the designs of people who follow the datasheet.What you're doing is equivalent to using undocumented APIs in an operating system. Your experimental data may show that the functions work perfectly, but there's a reason they're left undocumented.
PS: Why aren't you experimenting with running it at 9V? That's just as valid, right...?
The datasheet clearly says that pin/chip damage may occur above 40mA (and that 40mA is a stress rating only and not recommended for long term use).
What I want to know and want what the data sheet does not specifically tell us includes, but is not limited to, the following:1) How long 40mA is safe for? (They tell use it's not safe for a long time, but how long is that, specifically. 1s, 10s, 1ms, 1us?. Most device datasheets give this kind of information. It is useful information.)2) They do not tell us what the recommended long term maximum output current is. (Is it 15mA, 20mA, 25mA, 30mA, 35mA)?
1) How long 40mA is safe for?
Most device datasheets give this kind of information.
They do not tell us what the recommended long term maximum output current is.
Rise and fall times of all outputs and under what test conditions
Inherent internal capacitance of each pin under the various possible configurations and under what test conditions.
I note that the specifications in these areas supplied by Microchip are better.
I agree it's important to test things, but even then to be aware of possible errors in your test procedures. That's why I am happy if my tests can be reproduced. And even happier if they are backed up by the theory behind the test.
I will also need to re-do my "short circuit" test.
It is not, the term absolute means absolute. You can read, it says 40mA is a stress rating only.
No they don't. The ones that do are for components designed to take high pulsed currents.
Yes they do, all the ratings are for 20mA.
Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady state conditions (non-transient), the following must be observed:ATmega48A/PA/88A/PA/168A/PA/328/P:1] The sum of all IOL, for ports C0 - C5, ADC7, ADC6 should not exceed 100mA.2] The sum of all IOL, for ports B0 - B5, D5 - D7, XTAL1, XTAL2 should not exceed 100mA.3] The sum of all IOL, for ports D0 - D4, RESET should not exceed 100mA.
Your right they don't say that. Do you understand why?
Please try and live in the real world.
So use their chips and stop beefing.
I think you would need to repeat the above general idea but have a short instead of the MOSFET. Then the scope trace (on the triggered point) should show you the instantaneous current during the "short" cycle.
I don't really want to make predictions, but my guess is that you might find it exceeds 88 mA for some nanoseconds and then drops back to 88 mA.
My guess is based on the fact that we have both measured more like 440 mA into the MOSFET for a short time. So it is reasonable to suppose we would see a similar if not greater amount into a short. How long before that drops back to (around) 88 mA would need to be experimentally verified.
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