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AD5781 - not working

shlomib
on Aug 13, 2015

Hi

I'm using the AD5781 for the first time, programming is done by ATE (something like FPGA, but more flexible).

I'm not getting any vout, it's set to 0 constantly.

Below is my schematics, and the signals driven to the chip.

signals from top to bottom :

LDAC

SDIN

SYNC

SCLK

In addition - RESET is toggled from 0 to 1, and remains high, after which the sync goes low.

There are 24 clock when SYNC is low, first 3 bits are '001' for write operation to DAC register,
then 18 bits of data that were calculated to produce 3.3v output, and 2 bits '0' LSB.

  • 0
    •  Analog Employees 
    on Aug 16, 2015 7:18 PM over 5 years ago

    Hi,

    Have you tried reading back the SDO signal? Reading the same code that was written after one command is an indication of a good part. Could you get a scope shot of the RESET pin together with the SYNC and LDAC? Also, I would like to verify if your clock speed is at 1MHz?

    Regards,

    Mark

  • 0
    •  Analog Employees 
    on Aug 18, 2015 9:50 AM over 5 years ago

    Hello Shlomi Bakish,

    before writing to the DAC Register, did you write to the Control Register and set OPGND and DACTRI to enable the DAC?  Without doing this, VOUT will be set to GND exactly as you describe.

    Regards,

    Roddy

  • 0 on Aug 20, 2015 1:25 PM over 5 years ago

    Hi Mark and Roddy

    Thanks for your help, initially I didn't write the control register, so I added this write also.

    I'm writing 0x200032 - can you confirm it's ok ?

    The next write I'm doing the DAC register write, which is in my case 0x1D74AC.

    During this write I'm capturing the SDO and I get the 0x32, which is the control register I wrote before.
    I also tried other values and got correct output on SDO.

    Next I'm doing NOP, SDIN is constant 0, and 24 clock are pulsed with SYNC low, I get back the
    24 bits I wrote to DAC register - 0x1D74AC. Is this expected ? the 3 bits of the register address are
    also there (D22:D20).

    SCLK is 1MHz as you can see in the scope screenshot. Also RESET is held low after power up,
    and goes high before the first SYNC goes low.

    So the device seems to be responsive but VOUT is still not changing... hope you have some more debug ideas for me.

    Thanks !

    Shlomi

  • 0 on Sep 24, 2015 3:48 PM over 5 years ago

    Hi shlomib,

    @

    I have the same problem with you. DAC can not work, and SDO outputs following the SDI signal.

    Do you resolve this problem? and how to resolve it?

    Thanks very much.

    @

  • 0
    •  Analog Employees 
    on Sep 28, 2015 12:20 AM over 5 years ago

    Hi Candy,

    Have you tried what Roddy() have suggested? Check your Control Register specially the DACTRI and the OPGND registers. They should be cleared for the DAC to operate in normal mode.

    Regards,

    Mark