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REF3220 sometimes outputs a stable voltage of 2.080V to 2.100V instead of 2.048V

BrianBrianBrian
Expert 1085 points
Other Parts Discussed in Thread: REF3220, DAC7718

Hi

I'm using a REF3220 to provide the reference voltage to a DAC7718 with OUT_F and OUT_S tied together since the trace length is only about 2cm. The ENABLE pin is pulled down to GND and is raised to +5V by a microcontroller to adhere to the DAC7718 power cycle requirements. Usually everything works just fine. However, sometimes (about 1 out of 5) times when I apply power to my board, after the microcontroller enables the REF3220, the voltage at the REF3220 output will be between 2.080V and 2.100V albeit stable. The REF3220 will continue to output this voltage even if I power cycle repeatedly and appears to be stuck here. I'm making measurements with an Agilent 34410A.

Do you have any suggestions of possible causes for this behavior?

Schematic: 

IN - bypassed with 1uF ceramic cap then through a ferrite bead then to the +5V output of a LDO regulator

ENABLE - tied to GND via a 47k resistor and connected to output pin of microcontroller with +5V logic levels

OUT_F + OUT_S - tied together and connected in series with a ferrite bead and then the DAC7718 VREF pins

GND_F+GND_S - tied together and connected to GND

Thank you!

  • 0
    Expert 1085 points

    Also, I should add the the microcontroller pulls the REF3220's enable pin up to +5V about 200ms after it starts up.

  • 0 in reply to BrianBrianBrian
    Expert 1085 points

    Just bumping this thread in the hope that I will get an answer.

    Cheers!

  • 0 in reply to BrianBrianBrian
    TI__Guru** 113705 points

    Hi Justin,

    This is one of those 'no man's land' type questions.  You have the REF3220 connected to a DAC7718.  The DAC7718 is supported by this forum, but the REF3220 is supported in the Precision Linear forum.  You might want to post the question there as well.

    A couple of things that I think could cause an issue is poor grounding and another is current starvation.  Poor grounding could be something simple like a cold solder joint, or more complicated with respect to PCB layout.  Current starvation can be a result of using ferrites on the supply input to ICs.  Often times a power up sequence can have short duration, fast rise time, high current demands that an inductance (ferrite) can choke.  This can sometimes cause startup issues.

    For troubleshooting, I would disconnect the load from the REF3220 to see if it is a loading issue that is causing the problem.  If you still have the problem, then I would look further at bypassing the ferrite, checking solder connections and analyzing PCB layout.

    Best regards,

    Bob B