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DAC8830: Operating at MAX VDD and REF voltages

Part Number: DAC8830

Hi,

I'm using DAC8830ID on my board.

I have connected to 5V to VDD and 5V to the REF pins of the DAC. But with the maximum (65535) set value in the DAC I'm able to get maximum of 4.8V output voltage.

So is there any limitations by the chip for operating with 5V or equal REF and VDD?

Please let me know ASAP.

Also can you please recommend an ADC that can be used with DAC8830 with better accuracy?

Thanks & Regards,

Nanjunda M

  • Hi Nanjunda,

    What is the load on the DAC output? This is an unbuffered voltage DAC with an output impedance of 6.25kΩ. If you are not buffering the output this could explain the voltage drop you are seeing. 

    I created a search of 18 - 20bit, SPI ADCs. There are about 25 results but you can further refine the search by filtering by the sample rate, input type or range you are looking for. The link is here.  

    Best,

    Katlynne Jones

  • Hi Mr Jones,

    Thanks for the response.

    Yes, I know it is unbuffered. We have a buffer at the output stage(AD8531ARTZ-REEL7) for supplying the 250mA. And the current consumption is expected to be about 100mA on average. But we have observed this issue without connecting to the end device as well where the consumption would be less than a few mA(multimeter).

    Thanks for the suggestions on the ADCs. I'll check the same.

    Regards,

    Nanjunda M

  • Hi Nanjunda,

    Thank you for the extra details. Can you let me know the voltages you see at the DAC output as well as the buffer output when the buffer's load is 100mA and when the buffer's load is a few nA? Maybe we can isolate if the problem is coming from the DAC or buffer.

    I also found this plot from the AD8531 datasheet and it looks like the voltage swing from the rail should be a few hundred mVs when the load current gets up to 100mA.

    Best,

    Katlynne Jones

  • Hi Mr. Jones,

    Thanks for the inputs.

    The voltage observed at the DAC as well as the buffer outputs were the same as the maximum voltage set at the DAC input. (4.83V max)

    Regarding AD8531, we are more considerate about the higher voltage. The lower voltage is not a worry for us at this point.

    Thanks & Regards,

    Nanjunda M

  • Hi Nanjunda,

    Can you share your schematic?

  • Hi Paul,

    Sure.

    We tried removing the snubber also (30E & 5nf to ground0.

    The SMA connector is connected to the end device.

    Regards,

    Nanjunda M

  • Hi,

    Did you measure the reference voltage to DAC?

    How DLI_VREF_5V is generated in your board? Is it driven from a low impedance source? Also are you getting correct voltages at other codes, say mid code?

    Regards,

    AK

  • Hi Akhilesh,

    Sorry for the delay.

    The Reference voltage was measured to be 4.98V

    The DII_vref-5V is generated from 6V with LDO( LT3045EDD).

    The voltage till mid-range was fine. Only at higher voltage its getting limited.

    Thanks & Regards,

    Nanjunda M

  • Hi Nanjunda,

    Let's try two experiments:

    1. Confirm the VDD and VREF voltage when the output is correct (maybe 1/4 scale).  Is VDD lower than VREF, even marginally? Can you increase VDD to 5.2V?

    2. Can you confirm if this looks like a headroom issue or a gain error? Please measure the output range in about 1/16 increments.  You might see something like this:

    Thanks,

    Paul