3.3V to 5V connectivity ?

Started by January 30, 2001

Has anybody taken any special precautions when attaching 5V logic devices to
the 3.3V ADSP-2189X devices? (Especially the EZKIT LITE but related to any
ADSP design)

I've got an LCD (see newbie question earlier) which has a 5V interface to a
Toshiba T6963 controller (later I'm going to use a SED1352 I think) and also
other 5V devices. Thus I have a mixture of 5V and 3.3V peripherals.

I think I can get away with the 3.3V logic levels being able to trigger the
logic 0 and 1 thresholds of the 5V system so long as I use the ADSP to drive
into the 5V peripheral.

It's the opposite direction though? 5V -> 3V? Is it best to use a FET
transistor level shifter?

5V_|\|_____|\|___|-----|___
|/| |/| |_____| |
|
|
-------
^ |
| |
5V system--- ------ 3V system

One signal diode and one shottky diode giving a total voltage drop of about
2V?

Does anyone recommend a better method or maybe a level converter chip/driver
that I can buffer the output of the DSP data/address bus with? Thanks

Pete



3.3V -> 5V: works without level shifter
5V -> 3.3V: use 74LVCxx

Best regards!
Ralf Heuser-Lindner
>Has anybody taken any special precautions when attaching 5V logic devices to
>the 3.3V ADSP-2189X devices? (Especially the EZKIT LITE but related to any
>ADSP design)


Hi !
The 74ALVT_ family from Phillis Semiconductors should do the job
The 74ALVT16244 is a high-performance BiCMOS product designed for VCC
operation at 2.5V or 3.3V with I/O compatibility up to 5V.

Regards
sigurdm

email:

> ----------
> From:
> Sent: Tuesday, January 30, 2001 8:51 AM
> To:
> Subject: [adsp] 3.3V to 5V connectivity ? > Has anybody taken any special precautions when attaching 5V logic
> devices to
> the 3.3V ADSP-2189X devices? (Especially the EZKIT LITE but related
> to any
> ADSP design)
>
> I've got an LCD (see newbie question earlier) which has a 5V
> interface to a
> Toshiba T6963 controller (later I'm going to use a SED1352 I think)
> and also
> other 5V devices. Thus I have a mixture of 5V and 3.3V peripherals.
>
> I think I can get away with the 3.3V logic levels being able to
> trigger the
> logic 0 and 1 thresholds of the 5V system so long as I use the ADSP
> to drive
> into the 5V peripheral.
>
> It's the opposite direction though? 5V -> 3V? Is it best to use a
> FET
> transistor level shifter?
>
> 5V_|\|_____|\|___|-----|___
> |/| |/| |_____| |
> |
> |
> -------
> ^ |
> | |
> 5V system--- ------ 3V system
>
> One signal diode and one shottky diode giving a total voltage drop
> of about
> 2V?
>
> Does anyone recommend a better method or maybe a level converter
> chip/driver
> that I can buffer the output of the DSP data/address bus with? > Thanks
>
> Pete > _____________________________________
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> "reply all" if you want your answer to be distributed to the entire
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Here are some replies I've had. I've collated them here on the list
for an aid to others when browsing the archives in the future. I hope
this is O.K.
Thanks to all

Regards
Pete

*** QUOTE from Al Clark **********
Do not drive 5V logic into a 2189m!

The 3.3V output will be fine for driving the display. Often with
LCDs, you don't really need to read. If this is the case, you are
fine.

The bus with maximum wait states will be too fast for a LCD display.

This means you should either use the PF & Flag Lines (I have done
this) or write to a 74xx device.

If you need to support both read and write use 74 logic (powered by
3.3V that is 5V fault tolerant). The 74VHC family (except the
74VHC245) and the LV families will work.

You use the PF lines as outputs. They are the D0-D7 lines.
FL are E, R/W etc.

You can use a 74VHC574 or 74VHC273 for the data bus method. The
advantage of the 273 is that you can tie the G lpin to reset to clear
the FFs.

*** QUOTE from Sigurd ************
The 74ALVT_ family from Phillis Semiconductors should do the job
The 74ALVT16244 is a high-performance BiCMOS product designed for VCC
operation at 2.5V or 3.3V with I/O compatibility up to 5V.

You should also look up the SN74LVCC4245A from Ti.

This 8-bit (octal) noninverting bus transceiver uses two separate
power-supply rails. The A port, VCCA, is dedicated to accept a 5-V
supply level, and the configurable B port, which is designed to track
VCCB, accepts voltages from 3 V to 5 V. This allows for translation
from a 3.3-V to a 5-V environment and vice versa. The SN74LVCC4245A
is designed for asynchronous communication between data buses. The
device transmits data from the A bus to the B bus or from the B bus
to the A bus, depending on the logic level at the direction-control
(DIR) input. The output-enable (OE\) input can be used to disable the
device so the buses are effectively isolated.
The SN74LVCC4245A is characterized for operation from -40C to 85C.


On Tue, 30 Jan 2001 09:51:26 +0200, wrote:

> Has anybody taken any special precautions when attaching 5V logic devices to
> the 3.3V ADSP-2189X devices? (Especially the EZKIT LITE but related to any
> ADSP design)

Since this problem isn't restricted to ADI DSP's, I'd suggest posting
your question on a more general electronics forum, such as the
comp.arch.embedded newsgroup, or one of the sci.electronics.*
newsgroups. I know the problem has come up in the design I work on and
we use 3v-tolerant logic in one direction and level shifters in the
other, but I don't know the details as I mainly deal with the software.
Much of our 5v logic is actually on a separate power supply and we both
optically couple to it and use differential transceivers for SPORT
connections, making the system very noise- and ESD-immune. This is
critical in a factory environment where a customer might accidentally
plug one's product into hostile electrical gear.




>Has anybody taken any special precautions when attaching 5V logic devices
>to
>the 3.3V ADSP-2189X devices? (Especially the EZKIT LITE but related to any
>ADSP design)

We use Fairchild LVX4245 translator devices between an ADSP-2187L and our 5V
sensor.

>
>I've got an LCD (see newbie question earlier) which has a 5V interface to a
>Toshiba T6963 controller (later I'm going to use a SED1352 I think) and
>also
>other 5V devices. Thus I have a mixture of 5V and 3.3V peripherals.
>
>I think I can get away with the 3.3V logic levels being able to trigger the
>logic 0 and 1 thresholds of the 5V system so long as I use the ADSP to
>drive
>into the 5V peripheral.
>
>It's the opposite direction though? 5V -> 3V? Is it best to use a FET
>transistor level shifter?
>
>5V_|\|_____|\|___|-----|___
> |/| |/| |_____| |
> |
> |
> -------
> ^ |
> | |
> 5V system--- ------ 3V system
>
>One signal diode and one shottky diode giving a total voltage drop of about
>2V?

ADI suggest a similar circuit in one of their app. notes. I forget which
one.

Leon --
Leon Heller, G1HSM Tel: (work): +44 1327 357824 (home): +44 1327 359058
Email: My web page:
http://www.geocities.com/leon_heller IRISYS Ltd: http://www.irisys.co.uk
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