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TS3A27518E: TS3A27518 interfacing with SD card

eli
Guru 13485 points
Part Number: TS3A27518E

See below questions I got:

Application: recording analog video to uSD CARD.

 We are evaluating TS3A27518E in our Lab and we have encountered following problem which needs URGENT attention.

 This is how signals + clk looks like when we bypass MUX:

And as you can see while rising edge of clock, data is Valid.

On the other Hand, when those signals pass through MUX, we got a violation:

You can see clock is moving relative to data and on the rising edge data is NOT VALID.

We can see that data is staying relative to each other in phase but clocking phase is shifting.

 

We would kindly appreciate any feedback regarding…

  • 0
    TI__Mastermind 45575 points
    Eli,

    1) Are you saying there is a ~8ns shift in phase in the top plot vs the bottom plot?

    2) What pins are the clock and data signals passing through the MUX, do you have a schematic? Does this behavior stay consistent if you change the pins that the clock and data go through the MUX?

    3) How many boards have this behavior? Have you tested with different ICs?

    4) The clock on the bottom picture looks distorted compared to the top picture. Your clock signal looks to be about 25MHz and the TS3A27518E bandwidth is 240MHz so I wouldn't expect that much distortion. Are there different layout routings between the top and bottom pictures that could be causing some extra capacitance?

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    Guru 13485 points

    AdadM

    1)      Yes, we saying there is a ~8ns shift in phase in the top plot vs the bottom plot.

    2)      Our schematic:

    As you can see, we need the VDR to be at the NC side as an input to the SD CARD at the COM side (we want to use it as a multiplexer with another Video input).

    We didn’t change the pins that the clock and data go through the MUX, is there is special suggestion to it?

    3)     We didn’t tested with different ICs, it is on bread board so there is no layout routings and to use another board is not relevant.

  • 0 in reply to eli
    Guru 13485 points

    There is no phase shift any more after changing the CLK with the DATA 2 .

    After adding resistors, the Circuit now works.

    I still want the TI Micro SD pins connections suggestion.

  • 0 in reply to eli
    TI__Mastermind 45575 points
    Eli,

    There isn't any thing different between the different signal paths and any signal can pass equally well through any channel. It is odd that swapping the clock and data lines solved the issue. I wonder if it is something to do with the bread board connections. If you change the connection back does the issue return?

    The TS3A27518E is a passive FET switch that can be thought of as a wire so there isn't any termination requirements for the switch. I would use the recommended terminations from either your video driver for the SD connector since it won't matter for the switch.

    Thank you,
    Adam