3.3V-5V level shifters

Joerg · Sep 25, 2008

qrk wrote:

On Wed, 24 Sep 2008 17:26:32 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

What's the jelly-bean level shifter du jour, the most popular?

Need to shift three sigs 3.3V to 5V and another three 5V to 3.3V. Stuff
us analog dudes normally don't do. The TXB0104 looks ok, so does the
74LVC4245. But the specs for both are horrible, incomplete at best. Not
much in drive levels mentioned, or just for one direction.

The topper is a comment in the TXB spec, "OE should be tied to GND
through a pulldown resistor; the minimum value of the resistor is
determined by the current-sourcing capability of the driver" That driver
is obviously on the chip. Duh! Of course they also forgot what to do if
not needed. Pull up? Leave open? Who knows. Well, maybe they had a
kegger the night before ...

Here's what seems to qualify as a datasheet these days:
http://focus.ti.com/lit/ds/symlink/txb0104.pdf

VOH and VOL at 20uA. Microamperes! Couldn't believe it.

Going from 5v to 3.3v is easy with Fairchild 74LCX541 and other parts
in the family. I've found that Fairchild seems to have more
interesting parts in jellybean digital, power FETs, and analog
switches.

AFAIK those are only 5V-tolerant but can't really drive 5V logic with
gusto on the other side.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Eeyore · Sep 25, 2008

John Larkin wrote:

Eeyore wrote:
Martin Riddle wrote:
"Joerg" <notthisjoergsch@removethispacbell.net> wrote

What's the jelly-bean level shifter du jour, the most popular?

Need to shift three sigs 3.3V to 5V and another three 5V to 3.3V.
Stuff us analog dudes normally don't do. The TXB0104 looks ok, so does
the 74LVC4245. But the specs for both are horrible, incomplete at
best. Not much in drive levels mentioned, or just for one direction.

The topper is a comment in the TXB spec, "OE should be tied to GND
through a pulldown resistor; the minimum value of the resistor is
determined by the current-sourcing capability of the driver" That
driver is obviously on the chip. Duh! Of course they also forgot what
to do if not needed. Pull up? Leave open? Who knows. Well, maybe they
had a kegger the night before ...

Here's what seems to qualify as a datasheet these days:
http://focus.ti.com/lit/ds/symlink/txb0104.pdf

VOH and VOL at 20uA. Microamperes! Couldn't believe it.

--
Regards, Joerg

I third the LV parts, should be fine either direction.
I vaguely remember something about Fairchild's tiny logic too.

Single gates on a chip you mean ? Have you seen the prices they charge for
them !

My inventory report is showing parts from 12 cents to 44 cents each,
depending on quantity purchased and function. There are plenty of
times when being to plop down 1 or 2 gates somewhere is real handy.

NL37WZ16 is a remarkable part for 27 cents. It's a fierce, sub-ns edge
rate triple buffer/driver in a US8 package. It easily violates US
export restrictions for fast pulse generators.

Maybe I should have said "have you seen the prices Farnell charge for them ?".
It may have improved since I last looked though.

Graham

Joerg · Sep 25, 2008

langwadt@fonz.dk wrote:

On 25 Sep., 21:08, Joerg <notthisjoerg...@removethispacbell.net
wrote:
qrk wrote:
On Wed, 24 Sep 2008 17:26:32 -0700, Joerg
notthisjoerg...@removethispacbell.net> wrote:
What's the jelly-bean level shifter du jour, the most popular?
Need to shift three sigs 3.3V to 5V and another three 5V to 3.3V. Stuff
us analog dudes normally don't do. The TXB0104 looks ok, so does the
74LVC4245. But the specs for both are horrible, incomplete at best. Not
much in drive levels mentioned, or just for one direction.
The topper is a comment in the TXB spec, "OE should be tied to GND
through a pulldown resistor; the minimum value of the resistor is
determined by the current-sourcing capability of the driver" That driver
is obviously on the chip. Duh! Of course they also forgot what to do if
not needed. Pull up? Leave open? Who knows. Well, maybe they had a
kegger the night before ...
Here's what seems to qualify as a datasheet these days:
http://focus.ti.com/lit/ds/symlink/txb0104.pdf
VOH and VOL at 20uA. Microamperes! Couldn't believe it.
Going from 5v to 3.3v is easy with Fairchild 74LCX541 and other parts
in the family. I've found that Fairchild seems to have more
interesting parts in jellybean digital, power FETs, and analog
switches.
AFAIK those are only 5V-tolerant but can't really drive 5V logic with
gusto on the other side.

something like this then http://www.fairchildsemi.com/ds/74/74LVX4245.pdf
?

it has dual supply, one for each side

Yep, or the LVC4245 I wanted to use.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

langwadt@fonz.dk · Sep 25, 2008

On 25 Sep., 21:08, Joerg <notthisjoerg...@removethispacbell.net>
wrote:

qrk wrote:
On Wed, 24 Sep 2008 17:26:32 -0700, Joerg
notthisjoerg...@removethispacbell.net> wrote:

What's the jelly-bean level shifter du jour, the most popular?

Need to shift three sigs 3.3V to 5V and another three 5V to 3.3V. Stuff
us analog dudes normally don't do. The TXB0104 looks ok, so does the
74LVC4245. But the specs for both are horrible, incomplete at best. Not
much in drive levels mentioned, or just for one direction.

The topper is a comment in the TXB spec, "OE should be tied to GND
through a pulldown resistor; the minimum value of the resistor is
determined by the current-sourcing capability of the driver" That driver
is obviously on the chip. Duh! Of course they also forgot what to do if
not needed. Pull up? Leave open? Who knows. Well, maybe they had a
kegger the night before ...

Here's what seems to qualify as a datasheet these days:
http://focus.ti.com/lit/ds/symlink/txb0104.pdf

VOH and VOL at 20uA. Microamperes! Couldn't believe it.

Going from 5v to 3.3v is easy with Fairchild 74LCX541 and other parts
in the family. I've found that Fairchild seems to have more
interesting parts in jellybean digital, power FETs, and analog
switches.

AFAIK those are only 5V-tolerant but can't really drive 5V logic with
gusto on the other side.

something like this then http://www.fairchildsemi.com/ds/74/74LVX4245.pdf
?

it has dual supply, one for each side

-Lasse

Joerg · Sep 26, 2008

kevin93 wrote:

On Sep 24, 5:26 pm, Joerg <notthisjoerg...@removethispacbell.net
wrote:
What's the jelly-bean level shifter du jour, the most popular?

...
The topper is a comment in the TXB spec, "OE should be tied to GND
through a pulldown resistor; the minimum value of the resistor is
determined by the current-sourcing capability of the driver" That driver
is obviously on the chip. Duh! Of course they also forgot what to do if
not needed. Pull up? Leave open? Who knows. Well, maybe they had a
kegger the night before ...
...

I think they are trying to explain that if you are driving the enable
from another device (not necessarily a 74LVC4245) you need to put a
pull-down on the enable to guarantee that it remains low (and thus the
74LVC4245 remains in high-z) during power transitions. It is not
related to any characteristic of the 74LVC4245 itself.

It wasn't the LVC spec, that one is not stellar either but ok. Sometimes
I wonder if anyone proof-reads these things. But I am not surprised.
Right after getting my degree I met an alumni somewhere at an airport or
railways station . He had received his masters about the same time but
had never done any hobby projects, IOW his knowledge base was all from
books and professors. "Hey, what are you doing these days?" ... "Hire on
at a big semiconductor manufacturer" ... "What are you doing there?" ...
"Writing application notes". I almost froze.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Joerg · Sep 26, 2008

Jon Slaughter wrote:

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:hVACk.1362$Ws1.1079@nlpi064.nbdc.sbc.com...
What's the jelly-bean level shifter du jour, the most popular?

Need to shift three sigs 3.3V to 5V and another three 5V to 3.3V. Stuff us
analog dudes normally don't do. The TXB0104 looks ok, so does the
74LVC4245. But the specs for both are horrible, incomplete at best. Not
much in drive levels mentioned, or just for one direction.

The topper is a comment in the TXB spec, "OE should be tied to GND through
a pulldown resistor; the minimum value of the resistor is determined by
the current-sourcing capability of the driver" That driver is obviously on
the chip. Duh! Of course they also forgot what to do if not needed. Pull
up? Leave open? Who knows. Well, maybe they had a kegger the night before
...

Here's what seems to qualify as a datasheet these days:
http://focus.ti.com/lit/ds/symlink/txb0104.pdf

VOH and VOL at 20uA. Microamperes! Couldn't believe it.

Look at the I2C spec, they do this using mosfets and is bidir.

Is that why I2C hangs so often ... ?

<duck and run ...>

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

kevin93 · Sep 26, 2008

On Sep 24, 5:26 pm, Joerg <notthisjoerg...@removethispacbell.net>
wrote:

What's the jelly-bean level shifter du jour, the most popular?

....
The topper is a comment in the TXB spec, "OE should be tied to GND
through a pulldown resistor; the minimum value of the resistor is
determined by the current-sourcing capability of the driver" That driver
is obviously on the chip. Duh! Of course they also forgot what to do if
not needed. Pull up? Leave open? Who knows. Well, maybe they had a
kegger the night before ...
....

I think they are trying to explain that if you are driving the enable
from another device (not necessarily a 74LVC4245) you need to put a
pull-down on the enable to guarantee that it remains low (and thus the
74LVC4245 remains in high-z) during power transitions. It is not
related to any characteristic of the 74LVC4245 itself.

kevin

Joerg · Sep 26, 2008

Didi wrote:

On Sep 25, 3:26 am, Joerg <notthisjoerg...@removethispacbell.net
wrote:
What's the jelly-bean level shifter du jour, the most popular?

Don't know that but recently I designed in some 74LVXC3245, yet to
power the first board with them, though. But I am pretty experienced
with that sort of thing and did not smell anything foul (and I hope
saying so now won't come and bite me in 2-3 weeks time when I
have the prototype board here...).

If it's any comfort my design is also a white-knuckle ride. Lots of
rather unorthodox high voltage stuff on there, all kinds of safety
interlocks like HV only to come up when +5V is at least 4.5V but only
when there is a full moon, and that sort of thing. Design -> layout ->
production. No breadboarding at all.

Need to shift three sigs 3.3V to 5V and another three 5V to 3.3V.

Will do - but will take two chips if you need to simultaneously
have both directions actively driven. The two sides are separately
powered which should make sure no thermal issues like those John
mentioned are to be expected.

The topper is a comment in the TXB spec, "OE should be tied to GND
through a pulldown resistor; the minimum value of the resistor is
determined by the current-sourcing capability of the driver" That driver
is obviously on the chip. Duh! Of course they also forgot what to do if
not needed. Pull up? Leave open? Who knows. Well, maybe they had a
kegger the night before ...

You must have overlooked something there. OE should be an input
only - must be held low for the drivers to be open - the drivers on
the 16 data pins, that is. Drive it high and all get tristated.

Not quite. Quote "When the output-enable (OE) input is low, all outputs
are placed in the high-impedance state. To ensure the high-impedance
state during power up or power down, OE should be tied to GND through a
pulldown resistor; the minimum value of the resistor is determined by
the current-sourcing capability of the driver."

Low is tri-state. Then further down, quote: "The TXB0104 is designed so
that the OE input circuit is supplied by VCCA."

Anyhow, that thing is too hokey for me. I kicked it out and replaced
with LVC4245A, two of them. Now I found out that SOT23 LED have all but
vanished. Darn ...

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Didi · Sep 26, 2008

On Sep 25, 3:26 am, Joerg <notthisjoerg...@removethispacbell.net>
wrote:

What's the jelly-bean level shifter du jour, the most popular?

Don't know that but recently I designed in some 74LVXC3245, yet to
power the first board with them, though. But I am pretty experienced
with that sort of thing and did not smell anything foul (and I hope
saying so now won't come and bite me in 2-3 weeks time when I
have the prototype board here...).

Need to shift three sigs 3.3V to 5V and another three 5V to 3.3V.

Will do - but will take two chips if you need to simultaneously
have both directions actively driven. The two sides are separately
powered which should make sure no thermal issues like those John
mentioned are to be expected.

The topper is a comment in the TXB spec, "OE should be tied to GND
through a pulldown resistor; the minimum value of the resistor is
determined by the current-sourcing capability of the driver" That driver
is obviously on the chip. Duh! Of course they also forgot what to do if
not needed. Pull up? Leave open? Who knows. Well, maybe they had a
kegger the night before ...

You must have overlooked something there. OE should be an input
only - must be held low for the drivers to be open - the drivers on
the 16 data pins, that is. Drive it high and all get tristated.

Didi

------------------------------------------------------
Dimiter Popoff Transgalactic Instruments

http://www.tgi-sci.com
------------------------------------------------------
http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/

Original message: http://groups.google.com/group/sci.electronics.design/msg/0dacf2ff0fd37552?dmode=source

Jim Thompson · Sep 26, 2008

On Wed, 24 Sep 2008 17:26:32 -0700, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

What's the jelly-bean level shifter du jour, the most popular?

Need to shift three sigs 3.3V to 5V and another three 5V to 3.3V. Stuff
us analog dudes normally don't do. The TXB0104 looks ok, so does the
74LVC4245. But the specs for both are horrible, incomplete at best. Not
much in drive levels mentioned, or just for one direction.

The topper is a comment in the TXB spec, "OE should be tied to GND
through a pulldown resistor; the minimum value of the resistor is
determined by the current-sourcing capability of the driver" That driver
is obviously on the chip. Duh! Of course they also forgot what to do if
not needed. Pull up? Leave open? Who knows. Well, maybe they had a
kegger the night before ...

Here's what seems to qualify as a datasheet these days:
http://focus.ti.com/lit/ds/symlink/txb0104.pdf

VOH and VOL at 20uA. Microamperes! Couldn't believe it.

Joerg · Sep 26, 2008

Jim Thompson wrote:

On Wed, 24 Sep 2008 17:26:32 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

What's the jelly-bean level shifter du jour, the most popular?

Need to shift three sigs 3.3V to 5V and another three 5V to 3.3V. Stuff
us analog dudes normally don't do. The TXB0104 looks ok, so does the
74LVC4245. But the specs for both are horrible, incomplete at best. Not
much in drive levels mentioned, or just for one direction.

The topper is a comment in the TXB spec, "OE should be tied to GND
through a pulldown resistor; the minimum value of the resistor is
determined by the current-sourcing capability of the driver" That driver
is obviously on the chip. Duh! Of course they also forgot what to do if
not needed. Pull up? Leave open? Who knows. Well, maybe they had a
kegger the night before ...

Here's what seems to qualify as a datasheet these days:
http://focus.ti.com/lit/ds/symlink/txb0104.pdf

VOH and VOL at 20uA. Microamperes! Couldn't believe it.

What's not to like about the 74LCX245?

Well, I am using the LVC4245 now. I like the two supplies on those, IOW
a "real" level translator. Got to deal with power sequencing though.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Didi · Sep 26, 2008

On Sep 26, 2:46 am, Joerg <notthisjoerg...@removethispacbell.net>
wrote:

....
.... Design -> layout -
production. No breadboarding at all.

Come to think of it, I have not used any breadboarding for my designs
either last 20 years or so... I had stopped breadboarding for some
time back then when SMT came in and made breadboarding impractical
anyway

.

....
You must have overlooked something there. OE should be an input
only - must be held low for the drivers to be open - the drivers on
the 16 data pins, that is. Drive it high and all get tristated.

Not quite. Quote "When the output-enable (OE) input is low, all outputs
are placed in the high-impedance state. To ensure the high-impedance
state during power up or power down, OE should be tied to GND through a
pulldown resistor; the minimum value of the resistor is determined by
the current-sourcing capability of the driver."

Low is tri-state. Then further down, quote: "The TXB0104 is designed so
that the OE input circuit is supplied by VCCA."

Oh I thought you were referring to the x245, I just don't know that
TXB0104 thing, my mistake.

Didi

------------------------------------------------------
Dimiter Popoff Transgalactic Instruments

http://www.tgi-sci.com
------------------------------------------------------
http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/

Original message: http://groups.google.com/group/sci.electronics.design/msg/4f9c2278d0270a7f?dmode=source

3.3V-5V level shifters

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