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DAC5682 SPI levels clamped at 1.8V

Valentin Popa
Intellectual 680 points

We drive the DAC5682 SPI bus from an FPGA 3.3V bank. We see the "1" SPI signal levels at around 3V before a 22 ohm series termination resistor, but after the termination resistor at the DAC5682 pin the "1" level is only at 1.8V.

The DAC5682 supply voltages as measured at the power pins are: Vdvdd = 1.8V, Viovdd=3.3V, Vavdd=3.3V

What could be the issue? Is the DAC5682 somehow clamping the levels at 1.8V?

Thank you,

Valentin

  • 0
    TI__Genius 17290 points

    Hi Valentin,

    There is no reason to think that the DAC would be causing this unless the DAC was damaged. Are there any other components on the SPI line after the 22 ohm resistor? Have you made sure that the absolute max ratings are not being exceeded? Are multiple boards showing this issue or just one? If you remove the 22 ohm resistor, what impedance is measured at the DAC SPI pins?

    Regards,
    Matt Guibord

  • 0 in reply to Matt Guibord
    Intellectual 680 points

    Hi Matt,

    The issue was a solder bridge underneath the DAC5682 - the SPI levels are at normal 3.3V level now.

    Thanks,

    Valentin