3.3V-5V level shifters

J

Joerg

Guest
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

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Joerg wrote:
What's the jelly-bean level shifter du jour, the most popular?
Click to expand...
74LVC07

BTW, I thought you are from Germany, not from India.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
 
Joerg 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.
Click to expand...
In the rare occasions in the past I've looked at it, LVCs looked a good bet.
There are some other LV parts too IIRC.

What's wrong with the specs ?

Graham
 
Vladimir Vassilevsky wrote:
Joerg wrote:
What's the jelly-bean level shifter du jour, the most popular?

74LVC07
Click to expand...
That would be open drain ...


BTW, I thought you are from Germany, not from India.
Click to expand...
Well, yeah, why? I am just not a digital guy. Just wanted to know what's
popular with the others.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Eeyore wrote:
Joerg 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.

In the rare occasions in the past I've looked at it, LVCs looked a good bet.
There are some other LV parts too IIRC.
Click to expand...
Thanks.


What's wrong with the specs ?
Click to expand...
Well, for example the example I posted. It's horrible or as you guys
say, horrid.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
On Thu, 25 Sep 2008 00:49:23 GMT, "Martin Riddle"
<martin_rid@verizon.net> 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.

--
Regards, Joerg

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

Cheers
Click to expand...
The Fairchild and OnSemi Tiny parts are mostly high-voltage tolerant
on their inputs (as in well over Vcc) so work fine in the 5-to-3.3
direction.

Going the other way, they'll work but get warm, unless you use the
Schmitt version, and then the levels might get iffy.

John
 
John Larkin wrote:


The Fairchild and OnSemi Tiny parts are mostly high-voltage tolerant
on their inputs (as in well over Vcc) so work fine in the 5-to-3.3
direction.

Going the other way, they'll work but get warm, unless you use the
Schmitt version, and then the levels might get iffy.
Click to expand...
We had that argument before. Driving the 5V HCT inputs from 3.3V levels
is the standard practice; the input gate cross conduction is about 1ma.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
 
Joerg 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.
Click to expand...
The 74LVC1T45 could be a good idea, too. I'm using this chip and I know
another company who uses it without problems. It converts a single signal,
only, but if you'll buy three of it, it might be less expensive than one
74LVC4245, and maybe easier for routing because it is smaller than a
24-TSSOP, if you need just three of it for one direction. But placement
costs might be higher.

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de
 
On Wed, 24 Sep 2008 20:17:08 -0500, Vladimir Vassilevsky
<antispam_bogus@hotmail.com> wrote:

John Larkin wrote:


The Fairchild and OnSemi Tiny parts are mostly high-voltage tolerant
on their inputs (as in well over Vcc) so work fine in the 5-to-3.3
direction.

Going the other way, they'll work but get warm, unless you use the
Schmitt version, and then the levels might get iffy.

We had that argument before. Driving the 5V HCT inputs from 3.3V levels
is the standard practice; the input gate cross conduction is about 1ma.
Click to expand...
I have some thermal images around here somewhere that are
interesting... a cute little row of hot spots. Some of the faster
parts can get downright toasty at 3.3 in, Vcc=5. The lower
power/slower ones are usually fine.

I don't want to argue; I just want to warn people to be careful about
this.

John
 
Martin Riddle 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.

--
Regards, Joerg

I third the LV parts, should be fine either direction.
I vaguely remember something about Fairchild's tiny logic too.
Click to expand...
Single gates on a chip you mean ? Have you seen the prices they charge for
them !

Graham
 
John Larkin wrote:
On Wed, 24 Sep 2008 20:17:08 -0500, Vladimir Vassilevsky
antispam_bogus@hotmail.com> wrote:


John Larkin wrote:


The Fairchild and OnSemi Tiny parts are mostly high-voltage tolerant
on their inputs (as in well over Vcc) so work fine in the 5-to-3.3
direction.

Going the other way, they'll work but get warm, unless you use the
Schmitt version, and then the levels might get iffy.
We had that argument before. Driving the 5V HCT inputs from 3.3V levels
is the standard practice; the input gate cross conduction is about 1ma.



I have some thermal images around here somewhere that are
interesting... a cute little row of hot spots. Some of the faster
parts can get downright toasty at 3.3 in, Vcc=5. The lower
power/slower ones are usually fine.

I don't want to argue; I just want to warn people to be careful about
this.
Click to expand...
That's exactly one reason why I asked here. There is a flurry of devices
out there and for some of them even the specs are iffy. Like one of them
that I almost picked (the TXB0104). It requires a "stiff" drive of 2ma
min. So it need a 1K pull-up when open and since the other guys insist
on series terminators .... meeeep ... out. Whew.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Frank Buss wrote:
Joerg 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 74LVC1T45 could be a good idea, too. I'm using this chip and I know
another company who uses it without problems. It converts a single signal,
only, but if you'll buy three of it, it might be less expensive than one
74LVC4245, and maybe easier for routing because it is smaller than a
24-TSSOP, if you need just three of it for one direction. But placement
costs might be higher.
Click to expand...
Thanks, Frank. But it's >15c, ouch. Maybe ok on this design though but
the LVC4245 is only around 30c. Placement costs are not such an issue
out here.

On this section my layouter is probably just going to hit the autoroute
button and then have a coffee :)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Frank Buss wrote:
Joerg 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 74LVC1T45 could be a good idea, too. I'm using this chip and I know
another company who uses it without problems. It converts a single signal,
only, but if you'll buy three of it, it might be less expensive than one
74LVC4245, and maybe easier for routing because it is smaller than a
24-TSSOP, if you need just three of it for one direction. But placement
costs might be higher.
Click to expand...
Hey, 6:43pm means 3:43am in Germany. When do you guys over there sleep ... ?

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
On Thu, 25 Sep 2008 04:02:49 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

Martin Riddle 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.

--
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 !

Graham
Click to expand...
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.

John
 
Joerg schrieb:

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.
Click to expand...
Any simple 74HCT gate will do the level shifting from 3.3 to 5 V. I have
used 74HCT08 in such cases (noninverting). Really cheap also, plus many
sources.

For converting 5 to 3.3V, just use a 5V tolerant 3.3V logic family -
74LVC is fine for this, for three signals I would again use a single
74LVC08. Or simply add (large enough) series resistors if the 3.3V input
impedance is high and speed is not critical...

However, you can of course also use single transistors for level
shifting (common base circuit). Works fine, but with the additionally
required resistors (and assembly expense) it's not cheaper than using
the ICs mentioned above. However, you'd have more flexibility for
placement and routing.

Tilmann
 
On Wed, 24 Sep 2008 17:26:32 -0700 Joerg
<notthisjoergsch@removethispacbell.net> wrote in Message id:
<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.
Click to expand...
How about the Fairchild 74LVX3245?
http://www.fairchildsemi.com/ds/74%2F74LVX3245.pdf
 
Joerg wrote:

Hey, 6:43pm means 3:43am in Germany. When do you guys over there sleep ... ?
Click to expand...
Currently it is a bit more work. The marketing of one of our clients has
produced some flyers for a product, which will be presented at a tradeshow
next monday and sent it to their end customers. I'm the programmer of the
firmware and I was amazed to see all the nice features. Unfortunately only
a subset was defined in the requirements specification. Now it's getting a
bit more expensive :)

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de
 
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.
Click to expand...
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.

Mark
 
Frank Buss wrote:
Joerg wrote:

Hey, 6:43pm means 3:43am in Germany. When do you guys over there sleep ... ?

Currently it is a bit more work. The marketing of one of our clients has
produced some flyers for a product, which will be presented at a tradeshow
next monday and sent it to their end customers. I'm the programmer of the
firmware and I was amazed to see all the nice features. Unfortunately only
a subset was defined in the requirements specification. ...
Click to expand...

Don't we all know that? "Hey, we need this new thingamagic that we saw
at a competitor and it's going to be easy, I think ..."


... Now it's getting a bit more expensive :)
Click to expand...
Ah, so now you can be found every night for dinner in the Kaeferschaenke :)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
JW wrote:
On Wed, 24 Sep 2008 17:26:32 -0700 Joerg
notthisjoergsch@removethispacbell.net> wrote in Message id:
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.

How about the Fairchild 74LVX3245?
http://www.fairchildsemi.com/ds/74%2F74LVX3245.pdf
Click to expand...

Thanks. Looks like the LVC4245 which is probably what I am going to use.

--
Regards, Joerg

http://www.analogconsultants.com/

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