Failing AD5372 DACs

I designed low noise 32-channel DAC modules for ion-trap applications.

And we observe that on some of the boards the DAC consumes much higher current on negative rail than specified.

I measure 60mA, this current heats the chip significantly and gets increased with every degree. At certain moment, the DAC and LDO gets hot and the LDO enters thermal shutdown. When I switch on cooling, the current gets back to 60mA and DAC works again.

When I cool the board intensively with fan, the current is stable but still roughly 60mA.

We compared the eval board with our board and so far found that on eval board the pin 13 (NC) is grounded which is floating on my board.

There are several boards that work perfectly OK with current consumption within specification.

The supply is generated from +/- 15V using two low noise LDOs which also supply the output amplifiers and filters.

Reference is also supplied from same +12V rail.

The voltages wake up in following sequence: 3.3V, +12V, -12V.

Here is full documentation including schematics and production files.

Releases · sinara-hw/Zotino · GitHub 

  • 0
    •  Analog Employees 
    on May 24, 2018 10:15 AM over 2 years ago

    Hi gkasprow,

    Can you answer the following questions for us to better understand the issue:

    • is the 60mA current measured at the trace going into the VSS pin?
    • when does the 60mA current occur? is it immediately after power-up?

    Best regards,

    Rainier

  • Yes, I measure it at the VSS pin. There is an LDO  and I made sure the current flows to the DAC.

    Yes, 60mA is immediately after power up. Then the DAC heats and the current increases until the LDO enters over-temperature protection. This particular DAC chip was working correctly for some time, with low power consumption but at certain moment started consuming high current.

  • 0
    •  Analog Employees 
    on Jun 18, 2018 10:15 AM over 2 years ago

    Hi gkasprow,

    If you are certain that the DAC is consuming the large current (60mA) at the VSS pin, you might want to check  if any of the bypass capacitors is shorted to ground, or if one of the 32 outputs of the DACs is shorted to ground.

    You can easily do this by performing diode checks on these pins while the devise is not powered.

    Best regards,

    Rainier

  • I observe this behaviour on a few boards.

    I'm sure the bypass capacitor is not shorted because the AD chip is heating, not capacitor.

    All outputs are driving high impedance loads - there are just active lowpass filters based on opamps.

    The board is working perfectly fine, all outputs produce correct voltage, but the chip heats a lot. An the only way to keep the power consumption within 60mA is to cool it with fan.

  • 0
    •  Analog Employees 
    on Jul 9, 2018 6:24 AM over 2 years ago

    Hi gkasprow,

    Apologies for the very late response.

    I just noticed that the EPAD on your schematic is connected to ground. The recommended connection for the EP is going to VSS. This may be the reason why you are getting a very large current on the negative rail.

    Best regards,

    Rainier