interfacing 3.3v to 5v using TI PCA9306 level translator??

[amico]

Hello all

can i use TI PCA9306 level translator in order

to interface NOA1302 3.3v light sensor with my microchip 5V PIC16F877 ??

attached relevent data sheets.

thanks,

amico

 

[M!k]

Re: interfacing 3.3v to 5v using TI PCA9306 level translator

No guarantee, but to me that looks OK now.

 

[amico]

Re: interfacing 3.3v to 5v using TI PCA9306 level translator

please see attached file

is this the right way to connect the devices??

amico

 

[wp100]

Re: interfacing 3.3v to 5v using TI PCA9306 level translator

Hi,

Well that translator data sheet says you need pull ups on both sides of the chip and according to the datasheet chart 4.7k is higher than anything they specify.

Have you seen that chip in a similar existing circuit design that you can use for reference ?

Don't know if you have either of those chips yet, but two other things to try - buy a 16LF877a which allows you to run everything direct at 3v3 - 4meg max speed though.

Also go to to Microchips site - they do a couple of good documents on 3 to 5 v translation.

 

[amico]

Re: interfacing 3.3v to 5v using TI PCA9306 level translator

attached more updated JPG.

the resistors values were chosen according to PICDEMO2 PLUS schematics (attached page 15 )

which use 4.7k resistors as pull up between the PIC16F877 and the temp sensor TC74.

ive taken the typical application of the PCA9306

Can someone please tell if it will work? if not, what should I change?

please note that I already bought this components, so please try to help on how to use the existing components.

Thank you for all your present and future input.

amico

 

[wp100]

Re: interfacing 3.3v to 5v using TI PCA9306 level translator

Hi,

Right, see what you are doing better - using the proven picdem design to set up your diy experiments.

I have not used that translator chip so cannot give a definative answer on the pull up resistors - some other members might know.

However I would first prove your circuit / program by just using the TC74 directly connected to the 16f877 with the 4k7 resistors on both clk and data lines.

Once you prove that your whole systems works ok, then try the translator and light chips with 4k7 pulls up on the pic side, but say 1k on the light sensor side - as its datasheet recomends.

If the values are not suitable you will just get garbage in your communications with the pic, so then you can try adjusting the values in line with the translators datasheet.

Even without pulls up there is little chance of any damage to the chips, its just that the level logic will float so giving false values .

As you can see, so many of the modern devices are running at 3 / 3v3 whereas many hobby circuits still use 5v designs so you always get this interface problem.

Thats why using a LF chip that can be run at either voltage is so handy, alternativley some of the newer pics run at 3v3 but they have some digital inputs that can accept 5v signals without further hardware - not much use for you now but something to consider for future projects.