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DAC81416-08EVM: ALMOUT LED on - cannot write values using GUI

Gowtham Mahendran
Prodigy 10 points
Part Number: DAC81416-08EVM
Other Parts Discussed in Thread: DAC81416

Tool/software:

Im new to DAC81416-08EVM module and was using GUI. It was working fine but now I got the ALMOUT LED on and I'm no longer getting output. The input signals are given externally as per the datasheet and I have verified with the test points. Vio = 3.3V, Vdd = 5V, Vcc = +12V, Vss = -12V and GND to common ground. Here are the jumpers I removed - J6, J7 and J8.The problem appeared after I switched from internal USB supply to external supply.

Here is what I set in GUI. The Green Dot appears and the DAC is connected. I enabled the bits for the device and all the individual channels  to max (FFFF). I set the range to +-10V to all the DAC. The GUI is set to write the output immediately. But no output is observed. How can I bring back to normal operation. Kindly help.

  • 0
    TI__Expert 5080 points

    Hi Gowtham,

    Can you please help with few things here before we can debug the board/device - 
    1. is SPI read operation is working for you?
    2. If yes, can you power up the device and bring up the internal reference on TP6?

    Thanks,
    Sanjay

  • 0 in reply to Sanjay
    Prodigy 10 points

    Dear Sanjay,

    1. is SPI read operation is working for you? No it is not working. The FTDI gets instanteously hot just after connecting the supply. I also verified that the external DC supply is stable. If i try with USB 1.8V for Vio, then ALMOUT LED is off.

    2.  If yes, can you power up the device and bring up the internal reference on TP6? - After powering up, the TP6 remains at zero and no change is observed.

    Right now, U5 got burnt while powering it with USB supply. The connections are made perfect but I have no reason why it burnt out. I will replace this shortly and come back here.

  • 0 in reply to Gowtham Mahendran
    TI__Expert 5080 points

    Hi Gowtham,

    U5 getting burnt might have happened due to incorrect power up of the EVM - VIO might have been powered on via both the LDO and external power supply.

    Regarding the FTDI, please confirm few things - 
    1. is FTDI driver installed ? 
    2. if yes, please check if it's getting detected in the device manager of the laptop/PC.
    3. if yes, let's schedule a debug session.

    Thanks,
    Sanjay 

  • 0 in reply to Sanjay
    Prodigy 10 points

    Dear Sanjay,

    I fixed the voltage regulator. The FTDI driver is installed and it is getting detected in the device manager. With the USB supply, VIO=1.8V, VDD=4V (If I measure at J6, it is 4.6V without jumper connector. Is there any issue here? To test this i gave external 5v after disconnecting the jumper J6, the source is changing to current control mode.. I dont know where it is getting shorted).

    could you help me fixing this?

    (Edited) - I found some resistors also burnt out. I will fix this and update here very soon.

    Best Regards,

    Gowtham

  • 0 in reply to Gowtham Mahendran
    TI__Expert 5080 points

    Hi Gowtham,

    Just to clarify - you are observing voltage drop with J6 jumper shorted and external VIO is hitting current limit on the power supply, right ? If it's correct then DAC81416 VIO power pin is damaged and shorted to GND. You have to change DAC81416 device. 

    Thanks,
    Sanjay

  • 0 in reply to Sanjay
    Prodigy 10 points

    Hi Sanjay,

    Thank you for your feedback. I would like to clarify my observations:
    • With the J6 jumper shorted, I do not see the external VIO supply hitting its current limit. VIO remains in voltage control mode during the test.
    • Instead, when I connect VDD, the VDD supply is the one that reaches the current limit, while VIO remains stable.
    Based on this behavior, it seems the issue may not be related to VIO being shorted, but rather something affecting the VDD rail. Could you please confirm if this interpretation is consistent with a possible device fault, or if you recommend additional checks?

    I checked and found that resistors R21, R32 and R39 lost. Does replacing this will have any effect? I am waiting for the resistor to arrive. Is it worth the wait or move forward to a new one.

                           

    Best Regards,

    Gowtham

  • 0 in reply to Gowtham Mahendran
    TI__Expert 5080 points

    Hi Gowtham,

    Can you please use the only the external power ports to power the EVM board and check the current for each power pins. Compare the power supply current with the data sheet numbers and numbers are off by significant amount. That will indicate if there is any fault with the device.

    From the new details that you shared in previous reply, VDD might be faulty here.

    When it comes to the R21, R32 and R39; these should be not affect anything. Having very low value of these will lead to digital IO levels drop in voltage.

    Thanks,
    Sanjay