tirsdag den 11. april 2023 kl. 17.01.21 UTC+2 skrev John Larkin:> On Tue, 11 Apr 2023 07:34:25 -0700 (PDT), Lasse Langwadt Christensen > <lang...@fonz.dk> wrote: > > >tirsdag den 11. april 2023 kl. 16.27.42 UTC+2 skrev John Larkin: > >> On Tue, 11 Apr 2023 14:30:47 +0100, Clive Arthur > >> <cl...@nowaytoday.co.uk> wrote: > >> > >> >On 11/04/2023 12:18, Clive Arthur 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? > >> >>> > >> >> > >> >> Series diode or two, pull down resistor. > >> >> > >> > > >> >Or single 1.8V series zener, if your 0V doesn't mind being ~0.7V or so. > >> What's the zener drop? > >> > >> What's the zener current? > >> > >> Where can I buy a 1.8v zener? > > > >https://www.mouser.dk/ProductDetail/Nexperia/BZX8850S-C1V8-QYL?qs=7D1LtPJG0i3BPC7qWB9brw%3D%3D > What will the zener voltage drop be in the proposed circuit?does it matter? if a simple resistor is somehow not good enough there's no point in not using a 5V tolerant buffer
Minimilist Level Shifting
Started by ●April 8, 2023
Reply by ●April 11, 20232023-04-11
Reply by ●April 11, 20232023-04-11
In article <gfra3idpgu69fmb7rfbv6et3dp9jphu5cm@4ax.com>, jjlarkin@highlandtechnology.com says...> > >Or single 1.8V series zener, if your 0V doesn't mind being ~0.7V or so. > > What's the zener drop? > > What's the zener current? > > Where can I buy a 1.8v zener? > > >Depending on the current some LEDs are in that range. You get a zener and a light to boot.
Reply by ●April 11, 20232023-04-11
tirsdag den 11. april 2023 kl. 17.38.41 UTC+2 skrev Ralph Mowery:> In article <gfra3idpgu69fmb7r...@4ax.com>, > jjla...@highlandtechnology.com says... > > > > >Or single 1.8V series zener, if your 0V doesn't mind being ~0.7V or so. > > > > What's the zener drop? > > > > What's the zener current? > > > > Where can I buy a 1.8v zener? > > > > > > > Depending on the current some LEDs are in that range. You get a zener > and a light to boot.an LED is missing the diode in the other direction
Reply by ●April 11, 20232023-04-11
On Tuesday, April 11, 2023 at 11:16:03 AM UTC-4, Lasse Langwadt Christensen wrote:> tirsdag den 11. april 2023 kl. 17.01.21 UTC+2 skrev John Larkin: > > On Tue, 11 Apr 2023 07:34:25 -0700 (PDT), Lasse Langwadt Christensen > > <lang...@fonz.dk> wrote: > > > > >tirsdag den 11. april 2023 kl. 16.27.42 UTC+2 skrev John Larkin: > > >> On Tue, 11 Apr 2023 14:30:47 +0100, Clive Arthur > > >> <cl...@nowaytoday.co.uk> wrote: > > >> > > >> >On 11/04/2023 12:18, Clive Arthur 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? > > >> >>> > > >> >> > > >> >> Series diode or two, pull down resistor. > > >> >> > > >> > > > >> >Or single 1.8V series zener, if your 0V doesn't mind being ~0.7V or so. > > >> What's the zener drop? > > >> > > >> What's the zener current? > > >> > > >> Where can I buy a 1.8v zener? > > > > > >https://www.mouser.dk/ProductDetail/Nexperia/BZX8850S-C1V8-QYL?qs=7D1LtPJG0i3BPC7qWB9brw%3D%3D > > What will the zener voltage drop be in the proposed circuit? > does it matter? if a simple resistor is somehow not good enough there's no point in not using a 5V tolerant bufferIf it makes anyone feel better, I did find the spec on the part involved. They allow 10 mA into the protection diodes for a pin and 120 mA total for a bank. But, since they have no app note or any further info in the data sheet, there is no specific exception given to the max Vin on the I/Os, beyond Vcc + 0.3V. There's also the power consumption issue. A resistor of any given value would have a power drain amount that varies 3 to 1 or more. The two resistor approach has better potential. The ratio of resistors would be something like 3:1, drawing limited current when high, and a low impedance for speed. But even a pair of 0402 parts is as large as the dual inverter. At this point, I'm good with the dual inverter with specified 5V tolerant I/Os. I'm not interested in exploring the analog properties of a large digital device. -- Rick C. -+-- Get 1,000 miles of free Supercharging -+-- Tesla referral code - https://ts.la/richard11209
Reply by ●April 11, 20232023-04-11
tirsdag den 11. april 2023 kl. 19.59.12 UTC+2 skrev Ricky:> On Tuesday, April 11, 2023 at 11:16:03 AM UTC-4, Lasse Langwadt Christensen wrote: > > tirsdag den 11. april 2023 kl. 17.01.21 UTC+2 skrev John Larkin: > > > On Tue, 11 Apr 2023 07:34:25 -0700 (PDT), Lasse Langwadt Christensen > > > <lang...@fonz.dk> wrote: > > > > > > >tirsdag den 11. april 2023 kl. 16.27.42 UTC+2 skrev John Larkin: > > > >> On Tue, 11 Apr 2023 14:30:47 +0100, Clive Arthur > > > >> <cl...@nowaytoday.co.uk> wrote: > > > >> > > > >> >On 11/04/2023 12:18, Clive Arthur 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? > > > >> >>> > > > >> >> > > > >> >> Series diode or two, pull down resistor. > > > >> >> > > > >> > > > > >> >Or single 1.8V series zener, if your 0V doesn't mind being ~0.7V or so. > > > >> What's the zener drop? > > > >> > > > >> What's the zener current? > > > >> > > > >> Where can I buy a 1.8v zener? > > > > > > > >https://www.mouser.dk/ProductDetail/Nexperia/BZX8850S-C1V8-QYL?qs=7D1LtPJG0i3BPC7qWB9brw%3D%3D > > > What will the zener voltage drop be in the proposed circuit? > > does it matter? if a simple resistor is somehow not good enough there's no point in not using a 5V tolerant buffer > If it makes anyone feel better, I did find the spec on the part involved. They allow 10 mA into the protection diodes for a pin and 120 mA total for a bank. But, since they have no app note or any further info in the data sheet, there is no specific exception given to the max Vin on the I/Os, beyond Vcc + 0.3V. There's also the power consumption issue. A resistor of any given value would have a power drain amount that varies 3 to 1 or more. >with the series resistor the current taken from the 5V ends up in the 3.3V so if 3.3V is made with a linear regulator from 5V it is not wasted
