Funny specification for CMOS input for microcontroller, unused inputs and slow transitions

Sorry, it's page 114

Horrible data sheet!

Sounds like standard CMOS inputs, no schmitts. There is no explicit suggestion of SCR latchup or high shoot-thru currents overheating the chip; the poorly-worded cautions seem to be about noise, although overheating is another hazard. The warnings are pretty much standard CMOS practice.

The data sheet doesn't mention allowable input pin current, which sometimes suggests a latchup hazard.

Schmitt, or not, CMOS inputs should not be floated (unless they have built-in pull-ups or pull-downs) because they are high impedance and can wander anywhere due to board leakage. ...Jim Thompson

rx130.pdf

alfunction (device malfunction)

hey can have excessive current in the input stage due to cross conduction

ices)

Instead of current, they list the voltage:

Qoute (page 41)

Do not input signals or an I/O pull-up power supply to ports other than 5-V tolerant ports while the device is not powered. The current injection that results from input of such a signal or I/O pull- up may cause malfunction and the abnormal current that passes in the device at this time may cause degradation of internal element s. Even if ?0.3 to +6.5 V is input to 5-V tolerant ports, it will not cause problems such as damage to the MCU.

Unqoute

So, 0.3V over whatever diode they have in the input

Cheers

Klaus

Sure, but it should not cause a malfunction. Some discrete schmitt triggers has a defined max cross conduction current, so in some cases it should be possible to leave it open, although it is not good engineering practice

Cheers

Klaus

The question is, how much current can you force into an ESD diode of a powered chip, before it latches up and fries? Some parts specify that; be cautious if they don't.

o malfunction (device malfunction)

o they can have excessive current in the input stage due to cross conductio n

devices)

ll-up may cause malfunction and the abnormal current that

ents.

ot cause problems such as damage to the MCU.

It's just another way to put it. 0.3V across the diode translates to a curr ent. I would rarther have the current specified, but the voltage is ok also , granted that the latchup state current really is temperature correlated

Cheers

Klaus

o malfunction (device malfunction)

o they can have excessive current in the input stage due to cross conductio n

devices)

ll-up may cause malfunction and the abnormal current that

ents.

ot cause problems such as damage to the MCU.

see for example the LM2901, page 6, note 3:

I love that comparator, cheap as s**** :-)

Cheers

Klaus

Nasty part. If any input pin goes much more than -0.3, all four comparators can go crazy.

j0100_rx130.pdf

on

t to malfunction (device malfunction)

, so they can have excessive current in the input stage due to cross conduc tion

er devices)

he

an 5-V tolerant ports while the device is not powered.

pull-up may cause malfunction and the abnormal current that

lements.

l not cause problems such as damage to the MCU.

Well, that's not a rare case. Almost all chips has SCR latchup in similar f ashion

Cheers

Klaus

Lately I like MCP6567, dual CMOS comparator in MSOP8. RRI, open drain out, fast. It allows up to +-2 mA on inputs without weirdness.

Sort of a modern 5V version of the LM319.

Cheers

Phil Hobbs

te:

ction

cuit to malfunction (device malfunction)

put, so they can have excessive current in the input stage due to cross con duction

other devices)

cit

g the

dard

than 5-V tolerant ports while the device is not powered.

I/O pull-up may cause malfunction and the abnormal current that

l elements.

will not cause problems such as damage to the MCU.

f a

at;

r fashion

Check this out:

Page 2 defines:

Qoute

Input Current (VIN

j0100_rx130.pdf

on

t to malfunction (device malfunction)

, so they can have excessive current in the input stage due to cross conduc tion

er devices)

he

an 5-V tolerant ports while the device is not powered.

pull-up may cause malfunction and the abnormal current that

lements.

l not cause problems such as damage to the MCU.

The LM139? (LM339 in dip?) That's always given me 'fits' with power on. I think I had to beef up the positive rail. (?) or RC delayed one rail?? A better behaved comparator would be nice.

George H.

e:

tion

uit to malfunction (device malfunction)

ut, so they can have excessive current in the input stage due to cross cond uction

ther devices)

it

the

ard

than 5-V tolerant ports while the device is not powered.

/O pull-up may cause malfunction and the abnormal current that

elements.

ill not cause problems such as damage to the MCU.

t;

BITD National used LM1xx/2xx/3xx to refer to the same chip in military, ind ustrial/automotive, and commercial temperature grades, respectively.

So the LM139 was the cerdip/metal can version of the 339, with the 239 in t he middle. So we have the LM111/211/311 comparator, LM109/209/309 regulato r, and so on.

A nice Schottky rectifier from each supply to ground fixes a lot of those s orts of ills.

For a somewhat faster cheap OC comparator, I use a certain number of LM319s and 311s, but I generally don't use a lot of comparators these days.

Cheers

Phil Hobbs

ote:

nction

rcuit to malfunction (device malfunction)

nput, so they can have excessive current in the input stage due to cross co nduction

other devices)

icit

ng the

gh

ndard

ch

r than 5-V tolerant ports while the device is not powered.

I/O pull-up may cause malfunction and the abnormal current that

al elements.

will not cause problems such as damage to the MCU.

of a

hat;

ndustrial/automotive, and commercial temperature grades, respectively.

the middle. So we have the LM111/211/311 comparator, LM109/209/309 regula tor, and so on.

sorts of ills.

I'll try a Schottky, (is a 1N5711 nice? or too small?) (I've often hung a cap on the output of the '399 to slow it down. Speed-wise.)

George H.

Well, consider something that's not 40 years old.