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TCA9617A: B-side to B-side adaptation stage

Etienne HAMON
Prodigy 30 points

Part Number: TCA9617A
Other Parts Discussed in Thread: ISO1540, TCA9509

Hi every one and thank's in advance the help you might provide, 

I'm working on some hardware where 2 TCA9617A are used in series on 2 separate boards connected together.

Unfortunatly, because of a design mistake, both board expose the B side of the repeater. I understand it does not work because of the static offset.

I'm trying to find a solution to this problem by perhaps placing an other reference of repeater or isolator  or something else in-between. 

I've tried an ISO1540 laying around in the lab, but the VIL and VOL don't match either. 

Any help is appreciated, 

Thanks, 

Etienne

  • 0
    TI__Guru* 79221 points

    Hey Etienne,

    Do you have a block diagram for your I2C bus?

    Are you looking for a pin to pin solution where you don't need to do a board revision?

    What is the max I2C frequency you are trying to support?

    Vcc levels before and after the 9617?

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 30 points

    Hi Bobby, thank you for the support, 

    Here is a block diagram of my setup :

    My I2C Bus is working at 400kHz. 

    It would be best for me to find a solution without doing a new board revision for now. Pin to Pin would be really great, yet i could not find an approriate part so far. That's why i'm looking for a component to place between both boards. 

    My voltage levels are 3.3V all th way. I use the 9617 as bus repeaters. 

    Thank's again for the help, 

    Etienne 

  • 0 in reply to Etienne HAMON
    TI__Guru* 79221 points

    Hey Etienne,

    It doesn't look like your block diagram uploaded.

    From the additional details it seems like the only potential p2p solution may be TCA9509 but This device was spec'd/designed for B side to be 1V larger than A side. If you were to use it at 3.3V on both sides then I think the ViLcA may shift lower. If the master/slaves on A side can drive the line low enough then this solution may work but would technically be outside of the recommended datasheet specs.

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 30 points

    Hey bobby thanks for your help. 

    The component you proposed might suite my need with minor adjustement. 

    I've seen along its datasheet that 2 TCA9509 can be connected B-Side to B-side. as long as the VCCA < VCCB-1 is true. So i belive making an interface allowing level shift from 3.3V (Aside) to 5V (Bside) then back from 5V(Bside) to 3.3V(Aside) will allow me to establish my i2C link.  


    I've attached differently my block diagram as well as the solution i think about. Do you have any thought on this ?

    Thanks again for the help. I did not came across this part during my search,

    Etienne6038.I2C.pptx

  • 0 in reply to Etienne HAMON
    TI__Guru* 79221 points

    Hey Etienne,

    Sorry for the delay in response.

    I took a look at the powerpoint you posted but I see a problem with the TCA9617A being connected to A side of TCA9509. B side of the 9617 has a static voltage offset and A side of the 9509 has an offset as well. This means the two sides cannot interface with each other.

    My suggestion is to depopulate one of the 9617's and repopulate it with a 9509 as they should be pin to pin with each other. If you try to have two seperate 9509s connected to 2 separate 9617s like in slide 2, you will likely run into an issue where VoLB of 9617 will not pass a low from A side of 9509 to B side of 9509.

    -Bobby