need a bidirectional level shifter

[craig239955_st]

Posted on May 05, 2007 at 05:09

need a bidirectional level shifter

[craig239955_st]

Posted on May 17, 2011 at 09:42

Hi,

I want to use a STR912 in combination with TTL IC's. I need a bidirectional level shifter (3.3V <-> 5V) for my GPIO's.

Any idea where I can find such a device.

Luc Vercruysse

[roger_lynx]

Posted on May 17, 2011 at 09:42

....I need a bidirectional level shifter (3.3V <-> 5V) for my GPIO's.

 

Any idea where I can find such a device...

Why?

STR91x's I/O is 5V tolerant (5.5V max), from datasheet first page:

5 V tolerant, 16 have high sink current (8 mA)

and section:

6.4 DC electrical characteristics.

In case I am missing something, check:

ti.com

[craig239955_st]

Posted on May 17, 2011 at 09:42

I agree, but I need a voltage shifter from 3.3V => 5V to drive my CMOS inputs...

Luc

[roger_lynx]

Posted on May 17, 2011 at 09:42

I want to use a STR912 in combination with TTL IC's....

 

I need a voltage shifter from 3.3V => 5V to drive my CMOS inputs

...and now I am confused like a baby in a topless bar!

:o

[craig239955_st]

Posted on May 17, 2011 at 09:42

OK TTL is not correct.(English is not my native...)

I mean that I want to use the STR912 to access 5V devices (all technologies, 74LS, 74HCT, CMOS ...)

I think CMOS is the worst case concerning input levels (input voltage seen as ''high'' is above 3.3V). For that reason I need voltage shift.

Luc

[richardmauruschat9]

Posted on May 17, 2011 at 09:42

look at 74LVC4245 :)

[k_arthur]

Posted on May 17, 2011 at 09:42

maybe 74LCX244 will help you

[akaiser9]

Posted on May 17, 2011 at 09:42

Unless the system is battery powered, pullup resistors should do the job as well.

[roger_lynx]

Posted on May 17, 2011 at 09:42

...worst case concerning input levels (input voltage seen as ''high'' is above 3.3V)

True. You may want to look at this:

http://focus.ti.com/lit/an/scea021a/scea021a.pdf

http://focus.ti.com/lit/an/scea021a/scea021a.pdf

>

but, it looks like you got some hints what to use already....

[craig239955_st]

Posted on May 17, 2011 at 09:42

Thanks for response and link !

All voltage level translation devices, I know, have a direction pin.

In my design, I have a small universal module PCB with the STR912 and some pheripheral devices around it (CAN buffer, RS485, RS232). This PCB will be plugged into different other ''motherboards'' (something alike you can find here

http://www.mikroe.com/en/tools/unids3/

)

The function of GPIO pins will be different from board to board.

So I want to keep the bidirectional pins without having to drive a DIR pin.

Pull up will not help the problem when I want to use the GPIO in push-pull mode.

Regards

Luc V