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JanVrkoslav's avatar
JanVrkoslav
Icon for New Contributor rankNew Contributor
4 years ago

Cyclone 10 LP JTAG galvanic isolation

Hello,

Cyclone 10 design guideline says:

JTAG pins in the Intel Cyclone 10 LP device are powered up by VCCIO. However, you
may need to use VCCA in some cases.
• For devices using VCCIO of 2.5, 3.0, and 3.3 V, all I/O inputs must maintain a
maximum AC voltage of 4.1 V because JTAG pins do not have the internal PCI
clamping diodes to prevent voltage overshoot. You must power up the VCC of the
download cable with a 2.5-V supply from VCCA.

I have to ensure that voltage on the JTAG pins is not above 4,1V. My VCCIO is 3,3V.

In my case is implemented galvanic isolation on the board. (FPGA -> Isolator -> USB blaster).

Iam sure that 3,3V power rail on my board will not exceed 3,5V.

And the question is: Do I have to use voltage level shifter between FPGA and ISOLATOR for TDO, TCK and TMS pins from 3,3V to 2,5V?

Thanks!

3 Replies

  • FvM's avatar
    FvM
    Icon for Super Contributor rankSuper Contributor
    4 years ago

    Your JTAG interface signals are sourced on board, thus it's quite simple to avoid overshoot that might violate input voltage range. I would add source side series termination with trace impedance (e.g. 50 to 70 ohm, including driver impedance).

    Frank

  • JanVrkoslav's avatar
    JanVrkoslav
    Icon for New Contributor rankNew Contributor
    4 years ago

    Hi,

    thanks for reply. In GPIO handbook is written that Dedicated configuration pins and JTAG pins do not support impedance matching or
    series termination.

    But I was asking why I MUST power up the device with 2,5V if Iam sure that my power rail will not exceed 4,1V. Thats possible issue of the USB blaster? Can I proceed with 3,3V levels or not?

    Thanks

    Jan

  • YuanLi_S_Intel's avatar
    YuanLi_S_Intel
    Icon for Regular Contributor rankRegular Contributor
    4 years ago

    Hi Jan


    It is recommended value from the datasheet. You can try with the other voltage with level shifter. However, user need to take the risk from using that.