• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 46 subscribers
  • Views 272 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DAC8564: How to use the 3rd pin

Mizuki Yoshida
Prodigy 10 points
Part Number: DAC8564


Tool/software:

I am having trouble with my DAC8564, which is generating heat of just under 100 degrees Celsius.
I suspect that the cause is the 3rd pin.
Currently, I have four DAC8564s on a PCB set on a raspberry pi 5, controlling pneumatic valves.
Since the pneumatic valve operates at 0-5V, I have designed the PCB so that the 5V from the raspberry pi 5 is connected to the 3rd pin of the DAC8564 as an external reference.
However, the datasheet of DAC8564 says “If you want to use the external reference, send the command to disable the internal reference to DAC8564 before connecting the external reference”.
Since my PCB have the conncection of the 5V of the raspberry pi5 and the 3rd pin of the DAC8564, this means that I have connected the external reference before sending the command to disable the internal reference to the DAC8564.
I wonder if the collision between the output of the internal reference from the DAC8564 and the input of the external reference is leading to the high heat generation.
Please tell me what behavior DAC8564 does when an external reference is input to pin 3 without sending a command to disable the internal reference.
AVDD is correctly connected to 5V.

  • +1
    TI__Mastermind 42273 points

    Hi Yoshida-san, 

    The 5V reference will sink current into the 2.5V reference. Depending on this current the device could heat up.

    Can you share the rest of your schematic? Are you able to send the command to disable the internal reference? 

    Best,

    Katlynne Jone

  • 0 in reply to Katlynne Jones
    Prodigy 10 points

    Hello Jone

    Thank you for the reply.

    The pdf includes the rest of the schematic.As I already mentioned, the 4 DAC 8564s work to drive the 16 pnuematic valves with raspberry pi 5.

    The 3rd pins of the DACs are connected to the 5V of raspi and the GND via the 10UF and 0.1UF condensers.

    The DAC8564 generates heat even when the PCB is connected to the raspberry pi5 without running any code.


    On the other hand, other chips such as the ADC MAC11632s and the level shifter 74AHC541 do not generate heat in standby mode.

    What do you think is the cause of the heat?

    Sincerely,

    Mizuki Yoshida

    6862.control_board.pdf

  • 0 in reply to Mizuki Yoshida
    TI__Mastermind 42273 points

    Hi Yoshida-san, 

    Are you able to send a command to disable the internal reference to check if the heat goes away once the two reference sources are no longer fighting each other? Or are you not able to communicate with the device? 

    The short circuit current of the reference is 100mA. So if the 5v raspberry pi supply will source 100mA (per DAC, and you have 4), then the DACs will sink that much current. Try to disable the internal reference. If this current is too high on startup then you'll need an external current limiting resistor to limit this current, or you can use the internal reference. 

    Best,

    Katlynne Jones

     

  • 0 in reply to Katlynne Jones
    Prodigy 10 points

    Hi Jones,

    I sent a signal to disable the internal reference, but the heat generation remained unchanged in all four units.
    I compared the circuit diagram (6862.control_board.pdf) with the data sheet, but there seems to be no problem with the wiring.

    Sincerely,

    Mizuki Yoshida

  • 0 in reply to Mizuki Yoshida
    TI__Mastermind 42273 points

    Hi Yoshida-san, 

    Have you confirmed that your write command is successful? Have you been able to set the DACs to an output other than 0V? 

    If so then the reference is not the cause of the issue. 

    I also verified that the pinout is correct based on the schematic you shared. 

    Are the DAC outputs connected to a load?

    Best,

    Katlynne Jones