7406 vs MUN5235DW - Page 1
Forum section: electronics / beginners

author: josip
author_rank: Regular Contributor
timestamp: February 27, 2024, 01:05:51 pm
content: Hi,On old digital (0V/5V) bus interface with two or more devices for output is used 7406 (out is pulled high by 1kohm). I need 4 signals, not 6. For 7406 (variation) minimum size AFAIK is SOIC. I prefer to use 2 MUN5235DW (Dual NPN BRT) instead. Is there anything (that I don't see) why 7406 is much better part (than MUN5235DW) for this?Regards,Josip

author: David Hess
author_rank: Super Contributor
timestamp: February 27, 2024, 03:18:36 pm
content: The 7406 and 74LS06 are faster. There is a reason On Semiconductor does not specify switching speed of the MUN5235DW.

author: josip
author_rank: Regular Contributor
timestamp: February 27, 2024, 06:20:07 pm
content: Quote from: David Hess on February 27, 2024, 03:18:36 pmOK, I can check switching speed with scope for both with identical setup.

author: MrAl
author_rank: Super Contributor
timestamp: February 27, 2024, 06:39:04 pm
content: Quote from: josip on February 27, 2024, 01:05:51 pmHello,The 7406 input is made to interface with TTL and the logic levels associated with those kinds of outputs. You'd have to check if the transistor package can work with that kind of input reliably over the expected temperature range.The output of the 7406 is fairly fast, with fast rise and fall times. The propagation time is very low also, and this would beat the bipolar solution by a long shot when the input goes low because bipolars can have a nasty storage time which can stretch the time out into the microseconds rather than the nanoseconds unless you use an anti-saturation clamp diode(s), which can, unfortunately, increase the logic low output.What this means then is it depends on what the 7406 is being driven by and what it has to drive. The levels and the timing have to match if any of those specs are important to the application. Without knowing the application it's not possible to say for sure so you'd have to check that.What all that means is that the transistor can replace the 7406 in some applications and not others so you'd have to do some careful testing. If this is for a large production run I'd be very, very, careful.

author: josip
author_rank: Regular Contributor
timestamp: February 27, 2024, 07:54:23 pm
content: Quote from: MrAl on February 27, 2024, 06:39:04 pmLogic signal for input (7406 or transistor base) is from 3.3V micro controller pin (few milliamps). 7406 or transistor are "shorting" to ground, signal pulled high (5V) by 1k resistor. I found that in similar setup as mine, was used bsv52 (in datasheet there is 10-20 ns turn-on-off time and this is fast enough). So I guess that I should take 74ls06. Digital is my area, not analog, probably is better to not make simple things more complicated.

author: David Hess
author_rank: Super Contributor
timestamp: February 28, 2024, 03:56:27 am
content: Quote from: josip on February 27, 2024, 07:54:23 pmThe BSV52 is a gold doped fast saturated switching transistor so one of the few parts that can compete with the speed of a 7406. TTL chips get their speed by also being gold doped. LS TTL forgoes gold doping and instead uses Baker clamping with Schottky diodes across the base-emitter junction of the transistors to keep them out of saturation.

author: MrAl
author_rank: Super Contributor
timestamp: February 28, 2024, 01:16:12 pm
content: Quote from: josip on February 27, 2024, 07:54:23 pmHi,Well, that's interesting. A 3.3 volt logic system driving a 5 volt logic system directly? That sounds like there will be some violation of logic levels without a level translator. I would think you should check the logic levels for the TTL versus the output of the 3.3 volt microcontroller, especially for the 'high' logic level. If the 3.3v system cannot always meet the spec of the TTL input, there could be problems that start up as temperature levels shift a little. However, I think there are TTL logic families that can work with a 3.3v system as input. You could check to make sure that is the case here.I do not think the rise and fall times are too much of an issue, but I guess they could be depending on how the bipolar is driven because the logic does not want to see an input that rises or falls too slowly unless it has a Schmitt Trigger input. The worst part is the storage time though which can increase the propagation time by a lot when the transistor is to be turned off. If the application is sensitive to that it could be a big problem.

author: Zero999
author_rank: Super Contributor
timestamp: February 28, 2024, 02:36:43 pm
content: What's wrong with the 74LS06?If non-inverting isn't an issue, then how about a J-FET in common gate configuration? You'll need something which can pass 5mA and cut-off at -3V, so perhaps the PN4391 will do?https://www.mouser.com/datasheet/2/68/pn4391-93-541430.pdfHere's a circuit I designed awhile ago.Level shift bi-direc J-FET 3V3 5V.aschttps://www.eevblog.com/forum/projects/using-a-mosfet-(2n7000)-as-a-logic-level-converter/msg4431652/#msg4431652

author: David Hess
author_rank: Super Contributor
timestamp: February 28, 2024, 11:56:06 pm
content: Quote from: MrAl on February 28, 2024, 01:16:12 pmThere is some variation between TTL logic families, but TTL logic inputs are compatible with 3.3 volt CMOS outputs and may be connected directly. TTL outputs should also be compatible with 3.3 volt CMOS inputs.

author: MrAl
author_rank: Super Contributor
timestamp: February 29, 2024, 06:30:47 pm
content: Quote from: David Hess on February 28, 2024, 11:56:06 pmHi,From what I have read over some time, 3.3v CMOS to 5v TTL is a case of "almost always works". For me that would not be a statement of enough reliability, although for some hobby work it could possibly be enough, and I have used that philosophy for some of my own hobby work just not for professional stuff. For my use I would use some interface device, but I don't have time at this very moment to look up the chips.It gets kind of complicated really, especially with temperature variations and connection line length. You can look into this more if you like I won't be able to until later or tomorrow. If I remember right, there are really, really good solutions that have no doubt attached to them.

author: edavid
author_rank: Super Contributor
timestamp: February 29, 2024, 06:44:44 pm
content: Quote from: David Hess on February 28, 2024, 11:56:06 pmSure, the threshold levels are compatible, but is the 3.3V output going to tolerate having current driven into it from the TTL input? I would like to have a 74HCT buffer stage in between.

author: Zero999
author_rank: Super Contributor
timestamp: February 29, 2024, 07:48:27 pm
content: Does it have to have pull-ups? If not, then why not use the 74HCT04 or if that's too slow the 74ACT04?If you need to keep the pull-ups, then there's the 74HCT05 and the faster 74ACT05.

author: edavid
author_rank: Super Contributor
timestamp: February 29, 2024, 08:34:48 pm
content: Quote from: Zero999 on February 29, 2024, 07:48:27 pmA small problem with the 74HCT05 is that OP said he wants to use 1K pullups, and it's only spec-ed for 4mA output. Of course OP didn't tell us his output load requirements.

author: David Hess
author_rank: Super Contributor
timestamp: March 01, 2024, 03:58:03 am
content: Quote from: MrAl on February 29, 2024, 06:30:47 pmIf it does not work, then something is broken. CMOS has no difficulty producing a rail-to-rail output while meeting the TTL pull down current requirements. The TTL voltage and current levels are easily within the capability of 3.3 volt CMOS. A 3.3 volt pull-up (2.2k for TTL, 10k for TTL LS) *might* help in some cases, but should not be necessary.TTL Input -1.6mA +40uA <0.8V >2.0VTTL LS Input -0.4mA +20uA <0.8V >2.0VTTL Output -16mA +400uA <0.4V >2.4VTTL LS Output -4.0mA +200uA <0.5V >2.7VQuote from: edavid on February 29, 2024, 06:44:44 pmTTL and LS outputs with no loading produce about 3.4 volts, and supply practically no current at that level, so they will not overdrive a 3.3 volt CMOS input.

author: edavid
author_rank: Super Contributor
timestamp: March 01, 2024, 04:06:56 am
content: Quote from: David Hess on March 01, 2024, 03:58:03 amI'm talking about the TTL input, not the output. OP's question involves a 3.3V CMOS output driving a TTL input. Looking at the 7406 schematic, I only see 1 diode drop. I don't think it's a great idea to connect a 3.3V CMOS output to a 4.4V source.https://www.ti.com/lit/ds/symlink/sn7406.pdf

author: MrAl
author_rank: Super Contributor
timestamp: March 01, 2024, 07:13:55 am
content: Quote from: David Hess on March 01, 2024, 03:58:03 amHi,Well as I mentioned, there are a lot of variables. One is the type of CMOS. Since the current is also a factor, the older CMOS may not work as well as the more modern CMOS. That's one example I can think of offhand.The terms 'might' and 'should' spell out the question of reliability which I had been mentioning. You are right it 'should' work, but that's not how I do things except when I do my own personal stuff. It's perfectly fine if you want to do it that way, no problem here.I guess I am coming from a background where I saw things that 'should' work but do not work because they were close to being right but not quite right. Some interesting examples too in the digital world.One I remember was a resistor value that helped to ensure a logic level was correct. The value was just on the edge of meeting the requirement. it took several years to weed this problem out.Another example is a case of using a synchronous counter in a circuit that should have had an asynchronous counter. The designer assume that there would always be noise somewhere in the circuit and that would keep the clock signal going. Well, one day it didn't. Took hours to find the problem. It was in a max power tracker solar project.Those problems did not originate in a design I did, but I can't claim that it was impossible in the past for me to make such a mistake too. In a design for Pfizer Pharmaceuticals, I used a capacitor to provide a pulse to another logic circuit when a button was pressed. It was a kind of quick decision though because the project was getting close to running late. I had everyone in the office try this button, and it worked for every one of them as well as myself. The units shipped, and when the gal who had to use the thing (a precision weight scale for measuring animal organ weights) when SHE pressed the button, she pressed it in a much gentler way which meant it went down slower. The capacitor value was too small so when she pressed it not enough current was able to flow to trigger the digital input it was supposed to work with.That meant a flight from New Jersey to Indiana to modify the design. That also meant carrying a CRT oscilloscope because there were no digital ones back then. Of course that cost the company money.

author: newbrain
author_rank: Super Contributor
timestamp: March 01, 2024, 11:38:03 am
content: Quote from: josip on February 27, 2024, 07:54:23 pmCan you use a 3.3V supply? If so, probably a74LVC06, or a combination of its 1G/2G siblings, could be a good choice: its outputs can be pulled up to 5.5 V (operating conditions, 6.5 V maximum), speed is high, current driving capabilities very good.It can be supplied at 5 V, but in that case the Vih is too high to be driven by 3.3 V CMOS logic.

author: David Hess
author_rank: Super Contributor
timestamp: March 01, 2024, 06:22:46 pm
content: Quote from: MrAl on March 01, 2024, 07:13:55 am3.3 volt CMOS meets the requirements for driving TTL and TTL LS better than TTL does. It is also better than 5 volt CMOS which may cause problems with TTL because of the multiple emitter inputs, but will work fine with TTL LS and the later variations. The multiple emitter inputs driven by 5 volt CMOS would not actually fail, but could draw excessive supply current.5 volt HCMOS running at 3.3 volts will work. The original high voltage CMOS running at 3.3 volts might have trouble meeting the pull-down current requirements.