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DS125DF111: DS125DF111 with SigCon Architect resp. I2C issue

Julian E
Prodigy 200 points

Part Number: DS125DF111
Other Parts Discussed in Thread: USB2ANY,

Hello, 

we are using the DS125DF111 on a custom SFP board in conjunction with a FPGA as the source and sink of datastream. We interfaced the DS125DF111 with the USB2ANY and SigCon Architect. Reading the default values of some registers (i.e. addr 0x01 shows 0x61) works fine. So we assume the physical I2C connection should not be an issue. When we turn on the signal from the FPGA a LED connected at the LOS pin of DS125DF111 illuminates, why we think there is a valid signal detected on DS125DF111. A second channel from the FPGA (configured identically) is looped back on our custom board and showes a valid link without errors in our IDE, which is why we also assume the signal from the first link is present at DS125DF111 input.

Nevertheless, the SigCon Architect software does not show that a signal is present at the input of our DS125DF111, which is in contrast to the LED. Also when we adjust some settings of DS125DF111 in SigCon Architect and read the concerning registers back, we only read the default values of the registers, not holding our settings any more. Why this?

  • 0
    TI__Mastermind 42138 points

    Hi Julian,

    Can you share your schematic?

    Thanks,

    Drew

  • 0
    Prodigy 200 points

    Hello Drew, 

    attached you can find the schematic.

    Best regards, 
    Julian

    Schematic_Prints.PDF

  • 0
    Prodigy 200 points

    Does anyone have an idea? Maybe the DS125F111 is broken, but to some registers I receive valid data...

  • 0 in reply to Julian E
    TI__Mastermind 42138 points

    Hi Julian,

    Apologies for the delay.  There are a few things in your schematic that stood out:

    • Can you confirm you have external 3.3V supply and are relying on internal 2.5V regulator, similar to diagram below.
    • ENSMB should be tied to VIN with 1kOhm to select SMBus slave mode
    • 1 kOhm pullup on SDA/SCL is stronger than usual, but probably is not the issue here.  Typical pullup is 2 kOhm-5 kOhm.
    • We would typically recommend connecting READ_EN to GND via 1kOhm

    In terms of most likely issue, I'd double check 2.5V and 3.3V supply voltages, then see if you can adjust ENSMB pin strap.

    Thanks,

    Drew

  • 0
    Prodigy 200 points

    Hello Drew,

    thanks for your suggestions. I can confirm, that the Vin voltage is 3.3V and on the Vdd pins I can measure the 2.5V. I will now try to implement your other two ideas regarding ENSMB and READ_EN to connect them via 1k and not directly to Vdd resp. GND. The I2C signals look good on the oscilloscope, as you noticed this should not be the problem.

    Best regards,
    Julian

  • +1 in reply to Julian E
    TI__Mastermind 42138 points

    Hi Julian,

    Thanks for the update.

    Please note that for ENSMB, it should be tied to VIN and not VDD.  The 4-level input voltage thresholds are relative to VIN.

    Looking forward to your update on this.

    Thanks,

    Drew

  • 0
    Prodigy 200 points

    Hello again, 

    I prepared a new PCB with the pullups to now 3.3V (Vin) and pulldown to GND. And it seems to work! At least the SigCon shows a signal detected. I think it was my fault to tie the IOs to 2.5V rather to 3.3V...

    Now I need to setup the PLL to lock to the signal.

    Thanks for your help!

    Best regards,
    Julian