Consider low Rds switches/muxes from AD, TI or Maxim. Sub 1-Ohm Rds is available; break-before-make operation guaranteed.
Vladimir Vassilevsky DSP and Mixed Signal Consultant
sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 18oh m RDS on.
be ok to parallel to get lower resistance. Also, it must not have to much crossover shoot-through (so probably schmitt trigger type) and must have lo w dissipation at high operational frequency (1-10MHz)
(from John Devereux, earlier this year)
Break-before-make.
DigiKey had competing parts, too.
-- Cheers, James Arthur
and sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 18ohm RDS on.
to be ok to parallel to get lower resistance. Also, it must not have to much crossover shoot-through (so probably schmitt trigger type) and must have low dissipation at high operational frequency (1-10MHz)
direction? :-)
I have E-mailed you a full copy of my chip design. Observe rules noted to descend/ascend hierarchy.
You can observe games I played to get 500mA full-H without crowbar.
Do not share... some here are intellectual thieves and pretenders to being "designers" ;-)
I did this whole thing on my Lenovo X61s. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
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| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
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I love to cook with wine. Sometimes I even put it in the food.
If a CMOS gate's input is roughly midway between Vcc and ground, both p-channel and n-channel fets can be partially turned on in the front end. Current "shots through" the fets from Vcc to ground. That can draw a lot of supply current and potentially heat up the chip. It always happens briefly when a normal, fast input transitions, but it can get much worse if an input transitions slowly, or parks at an intermediate voltage. Schmitt-trigger gates are designed for slow inputs, so generally have moderate peak shoot-through currents.
Paralleling Schmitts is interesting. At some input voltage, some of the gates will see a "1" and some may see a "0", so their paralleled outputs will fight one another and pull a *lot* of supply current. Running the signal through one Schmitt section, and then driving a bunch more sections in parallel, is safer.
We almost fried some Tiny Logic gates, powering them from +5 but driving them from 3.3 volt logic from an FPGA. They got really hot.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 18ohm RDS on.
ok to parallel to get lower resistance. Also, it must not have to much crossover shoot-through (so probably schmitt trigger type) and must have low dissipation at high operational frequency (1-10MHz)
(Power dissipation capacitance, but no information on the unit. Icc = Cpd * V * f.
As Fred notes, CPD is equivalent picofarads. But it only applies for fast input transitions. I'm not sure if you are concerned about slow input edges.
Wimpier logic families (slower, weaker current drive) tend to have lower equivalent CPDs. The WZ parts are fierce.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 18ohm RDS on.
ok to parallel to get lower resistance. Also, it must not have to much crossover shoot-through (so probably schmitt trigger type) and must have low dissipation at high operational frequency (1-10MHz)
Abs max Vcc is 6.5. What's your problem?
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 18ohm RDS on.
ok to parallel to get lower resistance. Also, it must not have to much crossover shoot-through (so probably schmitt trigger type) and must have low dissipation at high operational frequency (1-10MHz)
But look at the capacitances! There's no free lunch.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 18ohm RDS on.
ok to parallel to get lower resistance. Also, it must not have to much crossover shoot-through (so probably schmitt trigger type) and must have low dissipation at high operational frequency (1-10MHz)
Talking about Digikey, they getting any better at stocking more of what they advertise? I have been leaning towards the other parts suppliers lately..
Jamie
This problem is greatly overstated. While ago I tested static cross conduction of HCT04 gate powered at +5V. The worst case was about 4mA, at 0.9V at the input.
Vladimir Vassilevsky DSP and Mixed Signal Consultant
sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 18ohm RDS on.
ok to parallel to get lower resistance. Also, it must not have to much crossover shoot-through (so probably schmitt trigger type) and must have low dissipation at high operational frequency (1-10MHz)
Worse. Some searches get below 10% in-stock. Many times a search will bring up parts that simply can't be had, ever. Why do they do that?
Another weirdness: expensive parts are available, and reasonably-priced parts aren't.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
that was my first thought, something like fan3111, but..
datasheet doesn't say what the dropout is, it maybe a bit slow for
10MHz and who knows how much power it will usemaybe a buffer/linedriver
-Lasse
...Jim Thompson
HC or HCT ?
TI
NL37WZ16. All three sections in parallel. The US8 package doesn't get rid of heat very well.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
sink.
so any powerloss is critical. Shoot through if a FET pair can easily go up to several amps, which won't be noticed if you are not looking.
A dual MOSFET (P-channel/N-channel pair) like Rohm EM6M2 can easily handle the task. If you add a couple of 2 ohm drain resistors, it limits the shoot-through to well under one amp, but the output resistance only gets two ohms drop (still well below your 5 ohm goal for 3.3V power supplies). Note the PFET has rather high capacitance, that's required to get the low on-resistance.
For best shoot-through limit, it gets complicated (you need something more than a logic drive, it takes turn-on delayed but turn-off prompt).
and sink.
so any powerloss is critical. Shoot through if a FET pair can easily go up to several amps, which won't be noticed if you are not looking.
the task.
well under one
5 ohmthat's
..Snip..
The EM6M2 has 1nC of gate charge. Running that at 5V and 200kHz will consume
1mW. I was trying to reduce the gate charge losses by using a logic ICOn that subject, anyone know the value of the gate charge for a run-of-the-mill gate inside a chip?
Regards
Klaus
and sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 1
8ohm RDS on.to be ok to parallel to get lower resistance. Also, it must not have to mu ch crossover shoot-through (so probably schmitt trigger type) and must have low dissipation at high operational frequency (1-10MHz)
For sure there are higher Rds(on) parts with lower capacitances, right? I was just throwing out an extreme example, since I'm an extremist :-).
I suspect the make-before-break convenience, integration, and capacitances in other switches will be attractive.
I didn't have time to screen parts--I mostly have to post and run these days.
James
ge
I've destroyed 74AC parts that way. Smoked 'em.
-- Cheers, James Arthur
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. ;-)
sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates to 18ohm RDS on.
be ok to parallel to get lower resistance. Also, it must not have to much crossover shoot-through (so probably schmitt trigger type) and must have low dissipation at high operational frequency (1-10MHz)
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.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
ce and sink. The tiny logic NL27WZ14 has 600mV drop at 32mA which equates t o 18ohm RDS on.
eed to be ok to parallel to get lower resistance. Also, it must not have to much crossover shoot-through (so probably schmitt trigger type) and must h ave low dissipation at high operational frequency (1-10MHz)
...
The lunch doesn't have to be free. If it's smaller, cheaper, and all wrapped up in a nicer box, that counts too.
-- Cheers, James Arthur
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