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DAC5682Z problem with B_equals_A mode

Jakub Korczyc
Prodigy 35 points
Other Parts Discussed in Thread: DAC5682Z, DAC5681Z, DAC5681

I am trying to make the DAC5682Z to output the same signal on A and B channel. I am using a custom made PCB.

I am providing the DAC with a 900MSPS data and a 900Mhz clock.

Settings:

PLL and DLL are disabled. FIRs are disabled. Single DAC mode set. B_equals_A is enabled. See configuration registers below.

Outputs of the DAC are pulled up to 3.3V using 50 Ohm resistor. I’m measuring them separately with Oscilloscopes (1Mohm input impedance). See picture below. Both channel A and B have the same output circuit.

My problem is:

I see signal on DAC output channel A but I don’t see anything on channel B.

It is not a soldering issue (I have the same issue on two boards).

Do you have an idea what might cause that?

I have also observed (possibly unrelated) unusual behaviour of DAC5682Z.

I am periodically reading the STATUS0 register of DAC5682Z. Sometimes device_ID(2:0) is ‘000’ (binary), as it should be, indicating the DAC5682Z.

But sometimes it is ‘111’ (binary) indicating the DAC5681Z (1 channel version).

Can it be connected to my main issue?

I would appreciate any help.

Settings:

STATUS0 0x03
CONFIG1 0x00
CONFIG2 0x00
CONFIG3 0x54
CONFIG4 0x00
CONFIG5 0x86
CONFIG6 0x0C
CONFIG7 0xFF
CONFIG8 0x00
CONFIG9 0x00
CONFIG10 0x00
CONFIG11 0x00
CONFIG12 0x00
CONFIG13 0x00
CONFIG14 0x00
CONFIG15 0x00

Circuit:

  • 0
    TI__Guru 66104 points
    Hi Jakub,

    I will take a look at your register settings and get back to you.

    -Kang
  • 0
    TI__Guru 66104 points

    Hi Jakub,

    I have checked in the lab with our DAC5682z EVM to see if operating under 1x1 mode (i.e. DAC5681z mode), the B_equals_A mode would work. After verifying on the bench, I have confirmed that the B_equal_A mode does *not* work in single DAC mode. This only works in dual DAC mode.

    I believe the original intention of the single DAC (1x1 mode) is meant for the DAC5682z to work as an DAC5681 or DAC5681z mode, which only has single DAC output on channel A. Therefore, whenever dual_DAC mode is set to 2b'0 for 1x1 mode, the equivalent logics for dual DAC mode will not work. If you look at the DAC5681z datasheet, the datasheet had listed the B_equals_A mode (config3, bit 2) to be fixed to 2b0 only.

    -Kang

  • 0 in reply to Kang Hsia
    Prodigy 35 points
    Thank you for answer.
    By the way my problems with confusing readouts of STATUS0 register were caused by fact that I left VFUSE pin floating (not connected to 1.8V as it should be)