Ricky <gnuarm.deletethisbit@gmail.com> wrote:> I'm tired of digging around looking for an optimal chip to level shift a > pair of signals from 5V TTL (an RS-422 transceiver) to 3.3V CMOS. There > are too many devices, and no small number of them are impacted by the > semiconductor shortage. But resistors are pretty available, as are Zener > diodes. > > So, I could use a pair of resistors to simply divide the TTL output > voltage to something safe for CMOS. But there's not much wiggle room, > given that the TTL output is not well specified. If the current through > the divider is minimized, this slows the signal edges. So a mA or two > needs to be flowing when the output is high, but not much more, because of > the power budget. > > Another option is to use a Zener diode. Most Zeners are specified at 5 to > 20 mA of current. Running at 1 mA is into the knee as best I can tell, not > desirable, resulting in poor regulation. > > I'm thinking with the variation in output voltage from the TTL output, the > Zener might not do much better than resistors. > > Any thoughts?I have 2 full unopened reels (2,500 pcs each) of SN74CBTD3384CDBQR parts that I have no use for if somebody needs those :) And yet another partial reel of 2,000 on top of those. That is 7K parts total. They are dirt chip, probably even cheaper than single 74LVC1G parts... And they are fast enough for PCI bus and beyond... --- ****************************************************************** * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * ******************************************************************
Minimilist Level Shifting
Started by ●April 8, 2023
Reply by ●April 9, 20232023-04-09
Reply by ●April 9, 20232023-04-09
On 2023-04-08 22:22, bitrex wrote:> On 4/8/2023 9:22 PM, Ricky wrote: >> I'm tired of digging around looking for an optimal chip to level shift >> a pair of signals from 5V TTL (an RS-422 transceiver) to 3.3V CMOS. >> There are too many devices, and no small number of them are impacted >> by the semiconductor shortage. But resistors are pretty available, as >> are Zener diodes. >> >> So, I could use a pair of resistors to simply divide the TTL output >> voltage to something safe for CMOS. But there's not much wiggle room, >> given that the TTL output is not well specified. If the current >> through the divider is minimized, this slows the signal edges. So a >> mA or two needs to be flowing when the output is high, but not much >> more, because of the power budget. >> >> Another option is to use a Zener diode. Most Zeners are specified at >> 5 to 20 mA of current. Running at 1 mA is into the knee as best I can >> tell, not desirable, resulting in poor regulation. >> >> I'm thinking with the variation in output voltage from the TTL output, >> the Zener might not do much better than resistors. >> >> Any thoughts? >> > > The common base shifter seems a good compromise between cost and > speed/power consumption: > > <https://next-hack.com/wp-content/uploads/2017/09/A5I9.png> > > And there's Jim Thompson's variant on it if the naked topology edges are > too slow: > > <https://electrooptical.net/static/oldsite/www.analog-innovations.com/SED/LogicLevelTranslator74HC14-RevA.pdf> >(mirror host takes bow) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●April 9, 20232023-04-09
On Sunday, April 9, 2023 at 4:44:14 PM UTC-4, Sergey Kubushyn wrote:> Ricky <gnuarm.del...@gmail.com> wrote: > > I'm tired of digging around looking for an optimal chip to level shift a > > pair of signals from 5V TTL (an RS-422 transceiver) to 3.3V CMOS. There > > are too many devices, and no small number of them are impacted by the > > semiconductor shortage. But resistors are pretty available, as are Zener > > diodes. > > > > So, I could use a pair of resistors to simply divide the TTL output > > voltage to something safe for CMOS. But there's not much wiggle room, > > given that the TTL output is not well specified. If the current through > > the divider is minimized, this slows the signal edges. So a mA or two > > needs to be flowing when the output is high, but not much more, because of > > the power budget. > > > > Another option is to use a Zener diode. Most Zeners are specified at 5 to > > 20 mA of current. Running at 1 mA is into the knee as best I can tell, not > > desirable, resulting in poor regulation. > > > > I'm thinking with the variation in output voltage from the TTL output, the > > Zener might not do much better than resistors. > > > > Any thoughts? > I have 2 full unopened reels (2,500 pcs each) of SN74CBTD3384CDBQR parts > that I have no use for if somebody needs those :) And yet another partial > reel of 2,000 on top of those. That is 7K parts total. > > They are dirt chip, probably even cheaper than single 74LVC1G parts... And > they are fast enough for PCI bus and beyond...That's what I used for the previous revision on the interface to the main board. But that's 3.3V now, so no more need. But I was running these to signals through that, which is why I'm looking for a 2 bit version. -- Rick C. ++- Get 1,000 miles of free Supercharging ++- Tesla referral code - https://ts.la/richard11209
Reply by ●April 10, 20232023-04-10
mandag den 10. april 2023 kl. 01.39.08 UTC+2 skrev Ricky:> On Sunday, April 9, 2023 at 4:44:14 PM UTC-4, Sergey Kubushyn wrote: > > Ricky <gnuarm.del...@gmail.com> wrote: > > > I'm tired of digging around looking for an optimal chip to level shift a > > > pair of signals from 5V TTL (an RS-422 transceiver) to 3.3V CMOS. There > > > are too many devices, and no small number of them are impacted by the > > > semiconductor shortage. But resistors are pretty available, as are Zener > > > diodes. > > > > > > So, I could use a pair of resistors to simply divide the TTL output > > > voltage to something safe for CMOS. But there's not much wiggle room, > > > given that the TTL output is not well specified. If the current through > > > the divider is minimized, this slows the signal edges. So a mA or two > > > needs to be flowing when the output is high, but not much more, because of > > > the power budget. > > > > > > Another option is to use a Zener diode. Most Zeners are specified at 5 to > > > 20 mA of current. Running at 1 mA is into the knee as best I can tell, not > > > desirable, resulting in poor regulation. > > > > > > I'm thinking with the variation in output voltage from the TTL output, the > > > Zener might not do much better than resistors. > > > > > > Any thoughts? > > I have 2 full unopened reels (2,500 pcs each) of SN74CBTD3384CDBQR parts > > that I have no use for if somebody needs those :) And yet another partial > > reel of 2,000 on top of those. That is 7K parts total. > > > > They are dirt chip, probably even cheaper than single 74LVC1G parts... And > > they are fast enough for PCI bus and beyond... > That's what I used for the previous revision on the interface to the main board. But that's 3.3V now, so no more need. But I was running these to signals through that, which is why I'm looking for a 2 bit version. >https://www.digikey.dk/da/products/detail/nexperia-usa-inc/74LVC2G34GM-115/1231594
Reply by ●April 10, 20232023-04-10
On 09/04/2023 15:44, John Larkin wrote:> On Sun, 9 Apr 2023 08:43:20 +0100, piglet <erichpwagner@hotmail.com> > wrote: > >> On 09/04/2023 02:22, Ricky wrote: >>> I'm tired of digging around looking for an optimal chip to level shift a pair of signals from 5V TTL (an RS-422 transceiver) to 3.3V CMOS. There are too many devices, and no small number of them are impacted by the semiconductor shortage. But resistors are pretty available, as are Zener diodes. >>> >>> So, I could use a pair of resistors to simply divide the TTL output voltage to something safe for CMOS. But there's not much wiggle room, given that the TTL output is not well specified. If the current through the divider is minimized, this slows the signal edges. So a mA or two needs to be flowing when the output is high, but not much more, because of the power budget. >>> >>> Another option is to use a Zener diode. Most Zeners are specified at 5 to 20 mA of current. Running at 1 mA is into the knee as best I can tell, not desirable, resulting in poor regulation. >>> >>> I'm thinking with the variation in output voltage from the TTL output, the Zener might not do much better than resistors. >>> >>> Any thoughts? >>> >> >> If the 3.3V input has a 5V tolerant ESD structure then of course no >> level shift is needed. If the 3.3V supply rail is stiff enough to accept >> a few mA injection then a series resistor might be all you need. For >> example 200 ohms would limit ESD diode current to 5mA and assuming 10pF >> input capacity would only slowdown 2ns, >> >> piglet >> >> > > 200 ohms was my suggestion! >Great minds think alike! :) piglet
Reply by ●April 10, 20232023-04-10
On Mon, 10 Apr 2023 13:03:46 +0100, piglet <erichpwagner@hotmail.com> wrote:>On 09/04/2023 15:44, John Larkin wrote: >> On Sun, 9 Apr 2023 08:43:20 +0100, piglet <erichpwagner@hotmail.com> >> wrote: >> >>> On 09/04/2023 02:22, Ricky wrote: >>>> I'm tired of digging around looking for an optimal chip to level shift a pair of signals from 5V TTL (an RS-422 transceiver) to 3.3V CMOS. There are too many devices, and no small number of them are impacted by the semiconductor shortage. But resistors are pretty available, as are Zener diodes. >>>> >>>> So, I could use a pair of resistors to simply divide the TTL output voltage to something safe for CMOS. But there's not much wiggle room, given that the TTL output is not well specified. If the current through the divider is minimized, this slows the signal edges. So a mA or two needs to be flowing when the output is high, but not much more, because of the power budget. >>>> >>>> Another option is to use a Zener diode. Most Zeners are specified at 5 to 20 mA of current. Running at 1 mA is into the knee as best I can tell, not desirable, resulting in poor regulation. >>>> >>>> I'm thinking with the variation in output voltage from the TTL output, the Zener might not do much better than resistors. >>>> >>>> Any thoughts? >>>> >>> >>> If the 3.3V input has a 5V tolerant ESD structure then of course no >>> level shift is needed. If the 3.3V supply rail is stiff enough to accept >>> a few mA injection then a series resistor might be all you need. For >>> example 200 ohms would limit ESD diode current to 5mA and assuming 10pF >>> input capacity would only slowdown 2ns, >>> >>> piglet >>> >>> >> >> 200 ohms was my suggestion! >> > >Great minds think alike! :) > >pigletAnd do things the easy way.
Reply by ●April 10, 20232023-04-10
On Monday, April 10, 2023 at 8:03:54 AM UTC-4, piglet wrote:> On 09/04/2023 15:44, John Larkin wrote: > > On Sun, 9 Apr 2023 08:43:20 +0100, piglet <erichp...@hotmail.com> > > wrote: > > > >> On 09/04/2023 02:22, Ricky wrote: > >>> I'm tired of digging around looking for an optimal chip to level shift a pair of signals from 5V TTL (an RS-422 transceiver) to 3.3V CMOS. There are too many devices, and no small number of them are impacted by the semiconductor shortage. But resistors are pretty available, as are Zener diodes. > >>> > >>> So, I could use a pair of resistors to simply divide the TTL output voltage to something safe for CMOS. But there's not much wiggle room, given that the TTL output is not well specified. If the current through the divider is minimized, this slows the signal edges. So a mA or two needs to be flowing when the output is high, but not much more, because of the power budget. > >>> > >>> Another option is to use a Zener diode. Most Zeners are specified at 5 to 20 mA of current. Running at 1 mA is into the knee as best I can tell, not desirable, resulting in poor regulation. > >>> > >>> I'm thinking with the variation in output voltage from the TTL output, the Zener might not do much better than resistors. > >>> > >>> Any thoughts? > >>> > >> > >> If the 3.3V input has a 5V tolerant ESD structure then of course no > >> level shift is needed. If the 3.3V supply rail is stiff enough to accept > >> a few mA injection then a series resistor might be all you need. For > >> example 200 ohms would limit ESD diode current to 5mA and assuming 10pF > >> input capacity would only slowdown 2ns, > >> > >> piglet > >> > >> > > > > 200 ohms was my suggestion! > > > Great minds think alike! :)Too bad they come up with the wrong answer. What will be the current when the TTL output is high? Does anyone consider the requirements? Parameter TEST CONDITIONS MIN TYP(1) MAX UNIT VOH High-level output voltage VID = 200 mV, IOH = –6 mA 3.8 4.2 V We'll see if that makes it through the usenet filter. Likely not. -- Rick C. +++ Get 1,000 miles of free Supercharging +++ Tesla referral code - https://ts.la/richard11209
Reply by ●April 10, 20232023-04-10
On 10/04/2023 3:32 pm, Ricky wrote:> On Monday, April 10, 2023 at 8:03:54 AM UTC-4, piglet wrote: >> On 09/04/2023 15:44, John Larkin wrote: >>> On Sun, 9 Apr 2023 08:43:20 +0100, piglet <erichp...@hotmail.com> >>> wrote: >>> >>>> On 09/04/2023 02:22, Ricky wrote: >>>>> I'm tired of digging around looking for an optimal chip to level shift a pair of signals from 5V TTL (an RS-422 transceiver) to 3.3V CMOS. There are too many devices, and no small number of them are impacted by the semiconductor shortage. But resistors are pretty available, as are Zener diodes. >>>>> >>>>> So, I could use a pair of resistors to simply divide the TTL output voltage to something safe for CMOS. But there's not much wiggle room, given that the TTL output is not well specified. If the current through the divider is minimized, this slows the signal edges. So a mA or two needs to be flowing when the output is high, but not much more, because of the power budget. >>>>> >>>>> Another option is to use a Zener diode. Most Zeners are specified at 5 to 20 mA of current. Running at 1 mA is into the knee as best I can tell, not desirable, resulting in poor regulation. >>>>> >>>>> I'm thinking with the variation in output voltage from the TTL output, the Zener might not do much better than resistors. >>>>> >>>>> Any thoughts? >>>>> >>>> >>>> If the 3.3V input has a 5V tolerant ESD structure then of course no >>>> level shift is needed. If the 3.3V supply rail is stiff enough to accept >>>> a few mA injection then a series resistor might be all you need. For >>>> example 200 ohms would limit ESD diode current to 5mA and assuming 10pF >>>> input capacity would only slowdown 2ns, >>>> >>>> piglet >>>> >>>> >>> >>> 200 ohms was my suggestion! >>> >> Great minds think alike! :) > > Too bad they come up with the wrong answer. What will be the current when the TTL output is high? Does anyone consider the requirements? > > Parameter TEST CONDITIONS MIN TYP(1) MAX UNIT > VOH High-level output voltage VID = 200 mV, IOH = –6 mA 3.8 4.2 V > > We'll see if that makes it through the usenet filter. Likely not. >I don't get your point? If the TTL Voh is 4.2V then the current in 200R would be 1mA (assuming 0.7V drop for the input clamp diode to 3.3Vdd) If even 1mA is too much then one could increase the resistor until RC delay becomes significant. piglet
Reply by ●April 10, 20232023-04-10
On Mon, 10 Apr 2023 17:30:33 +0100, piglet <erichpwagner@hotmail.com> wrote:>On 10/04/2023 3:32 pm, Ricky wrote: >> On Monday, April 10, 2023 at 8:03:54?AM UTC-4, piglet wrote: >>> On 09/04/2023 15:44, John Larkin wrote: >>>> On Sun, 9 Apr 2023 08:43:20 +0100, piglet <erichp...@hotmail.com> >>>> wrote: >>>> >>>>> On 09/04/2023 02:22, Ricky wrote: >>>>>> I'm tired of digging around looking for an optimal chip to level shift a pair of signals from 5V TTL (an RS-422 transceiver) to 3.3V CMOS. There are too many devices, and no small number of them are impacted by the semiconductor shortage. But resistors are pretty available, as are Zener diodes. >>>>>> >>>>>> So, I could use a pair of resistors to simply divide the TTL output voltage to something safe for CMOS. But there's not much wiggle room, given that the TTL output is not well specified. If the current through the divider is minimized, this slows the signal edges. So a mA or two needs to be flowing when the output is high, but not much more, because of the power budget. >>>>>> >>>>>> Another option is to use a Zener diode. Most Zeners are specified at 5 to 20 mA of current. Running at 1 mA is into the knee as best I can tell, not desirable, resulting in poor regulation. >>>>>> >>>>>> I'm thinking with the variation in output voltage from the TTL output, the Zener might not do much better than resistors. >>>>>> >>>>>> Any thoughts? >>>>>> >>>>> >>>>> If the 3.3V input has a 5V tolerant ESD structure then of course no >>>>> level shift is needed. If the 3.3V supply rail is stiff enough to accept >>>>> a few mA injection then a series resistor might be all you need. For >>>>> example 200 ohms would limit ESD diode current to 5mA and assuming 10pF >>>>> input capacity would only slowdown 2ns, >>>>> >>>>> piglet >>>>> >>>>> >>>> >>>> 200 ohms was my suggestion! >>>> >>> Great minds think alike! :) >> >> Too bad they come up with the wrong answer. What will be the current when the TTL output is high? Does anyone consider the requirements? >> >> Parameter TEST CONDITIONS MIN TYP(1) MAX UNIT >> VOH High-level output voltage VID = 200 mV, IOH = �6 mA 3.8 4.2 V >> >> We'll see if that makes it through the usenet filter. Likely not. >> > >I don't get your point? If the TTL Voh is 4.2V then the current in 200R >would be 1mA (assuming 0.7V drop for the input clamp diode to 3.3Vdd) > >If even 1mA is too much then one could increase the resistor until RC >delay becomes significant. > >pigletReal 74xx style TTL doesn't pull up hard. Modern CMOS will tolerate 50 mA into its ESD diodes and not latch up. A direct connection would work fine. Yes, add 200 ohms for the faint of heart (or the math impaired.)
Reply by ●April 10, 20232023-04-10
Ricky <gnuarm.deletethisbit@gmail.com> Wrote in message:r> I'm tired of digging around looking for an optimal chip to level shift a pair of signals from 5V TTL (an RS-422 transceiver) to 3.3V CMOS. There are too many devices, and no small number of them are impacted by the semiconductor shortage. But resistors are pretty available, as are Zener diodes. So, I could use a pair of resistors to simply divide the TTL output voltage to something safe for CMOS. But there's not much wiggle room, given that the TTL output is not well specified. If the current through the divider is minimized, this slows the signal edges. So a mA or two needs to be flowing when the output is high, but not much more, because of the power budget. Another option is to use a Zener diode. Most Zeners are specified at 5 to 20 mA of current. Running at 1 mA is into the knee as best I can tell, not desirable, resulting in poor regulation. I'm thinking with the variation in output voltage from the TTL output, the Zener might not do much better than resistors. Any thoughts? -- Rick C. - Get 1,000 miles of free Supercharging - Tesla referral code - https://ts.la/richard11209I use the M74VHC1GT50 an there's plenty in stock. Cheers -- ----Android NewsGroup Reader---- https://piaohong.s3-us-west-2.amazonaws.com/usenet/index.html
