Low RDSon Logic CMOS Gate

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Even a break-before-make CMOS analog switch has several CMOS gate
driver sections, each of which will have shoot-through. Then the final
switch capacitance behaves just like a Cpd effect, wasting energy on
every transition. No free lunch.

The lunch doesn't have to be free. If it's smaller, cheaper, and all
wrapped up in a nicer box, that counts too.

 

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HCT stuff isn't tuned for speed so has little crossover current (none,
ideally).  AC logic is a whole different kettle.  Better decouple AC gates
well.   ;-)

I was experimenting using one as a VHF amplifier. That works well,
until the smoke comes out. Another guy put a resistor in the supply
line with some success.

I switched to 'HC. Cool as a cucumber, and it just worked.

 

[Klaus Kragelund]

I was experimenting using one as a VHF amplifier. That works well,

until the smoke comes out. Another guy put a resistor in the supply

line with some success.



I switched to 'HC. Cool as a cucumber, and it just worked.

Some measurements of supply current:

For NC7SZ14:

100kHz, 3 gates in parallel, one gate feeding the 3 gates for fast switching of inputs, no output load:

3.3V, 366uA
5V, 1400uA

1MHz:

3V3,1280uA
5V, 3100uA

Cheers

Klaus

 

[Jon Kirwan]

Some measurements of supply current:

For NC7SZ14:

100kHz, 3 gates in parallel, one gate feeding the 3 gates
for fast switching of inputs, no output load:

3.3V, 366uA
5V, 1400uA

1MHz:

3V3,1280uA
5V, 3100uA

Linear assumption, then:

3.3V: I = 265uA + 1.02uA*f (in kHz)
5.0V: I = 1210uA + 1.89uA*f (in kHz)

Jon

 

[Fred Bartoli]

Jon Kirwan a écrit :

Linear assumption, then:

3.3V: I = 265uA + 1.02uA*f (in kHz)
5.0V: I = 1210uA + 1.89uA*f (in kHz)

Jon

Which seems a lot...
Also, the "static" (1210uA) current is way too big.

1.89uA/kHz -> 1.89nC/switch event and a *big* 380pF Cpd under 5V

380pF/4 gates, mean 95pF/gate which is 3 time the Fairchild figure...

 

[Klaus Kragelund]

Jon Kirwan a écrit :





Which seems a lot...

Also, the "static" (1210uA) current is way too big.



1.89uA/kHz -> 1.89nC/switch event and a *big* 380pF Cpd under 5V



380pF/4 gates, mean 95pF/gate which is 3 time the Fairchild figure...

The static consumption is unmeaserable (or at least below 1uA)

Regarding the high consumption, they are in parallel, so might be cross conduction from device to device if propagation times are no equal

I'll dig further and post back here

Cheers

Klaus

 

[[email protected]]

I was experimenting using one as a VHF amplifier. That works well,
until the smoke comes out. Another guy put a resistor in the supply
line with some success.

Right. AC has a significant and intentional crossover current for speed.

I switched to 'HC. Cool as a cucumber, and it just worked.

HC does not.

 

[Fred Bartoli]

Klaus Kragelund a écrit :

The static consumption is unmeaserable (or at least below 1uA)

Of course the static current is that small. That's why I did put quotes.
I meant the Jon_fitted_current_at_frequency_zero ...

Regarding the high consumption, they are in parallel, so might be cross conduction from device to device if propagation times are no equal

My thought too.

I'll dig further and post back here

If you have time, more than 2 frequency points will be interesting
because of the big "F=0 current" ...

 

[Fred Bartoli]

John Larkin a écrit :

Abs max Vcc is 6.5. What's your problem?

I was using that one:

http://www.nxp.com/products/logic/schmitt_triggers/74LVC14ABQ.html

You're right, for the Abs max, but its normal operation range is stated
as up to 3.6V