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REF70: total integrated noise value

Matteo Ricci
Prodigy 210 points
Part Number: REF70
Other Parts Discussed in Thread: REF6225, , DAC81404, , OPA196, REF54, REF50E

Tool/software:

Hi team,

i'm evaluating the precision reference voltage REF7025 and REF6225 to generate a reference voltage of +2.5V for the DAC81404.

In the datasheet of the REF7025 there are:

  • low frequency noise (1/f noise) of 0.23 ppm in (0.1-10) Hz
  • output voltage noise of 0.35 ppm_rms in (10 Hz - 1 kHz).

So, if the reference output voltage is +2.5V, 0.23 ppm and 0.35 ppm correspond to 0.575 uVpp and 0.875 uVrms respectively. Is it correct?

In the datasheet of the REF6225 there is the total integrated noise of 5 uVrms, but this parameter is not present in the datasheet of the REF7025. So, what is the value of this parameter for the REF7025?

The REF62xx family of voltage references have an integrated low output impedance buffer; therefore, there is no need for an external buffer while driving the REF pin of an high voltage reference DAC. So, i expect the total noise of the REF6225 is higher than the REF7025. Is it correct?

Finally, which of the 2 devices recommended to drive the DAC81404?

Thank you in advance.

Best Regards,

Matteo Ricci

  • 0
    TI__Expert 7910 points

    Hi Matteo,

    Thanks for reaching out with your questions.

    Matteo Ricci said:
    So, if the reference output voltage is +2.5V, 0.23 ppm and 0.35 ppm correspond to 0.575 uVpp and 0.875 uVrms respectively. Is it correct?

    This is correct.

    Matteo Ricci said:
    In the datasheet of the REF6225 there is the total integrated noise of 5 uVrms, but this parameter is not present in the datasheet of the REF7025. So, what is the value of this parameter for the REF7025?

    For noise above 1kHz you can refer to figure 7-20 in the REF70 datasheet. The corresponding figure in the REF6225 datasheet is Figure 13.

    Matteo Ricci said:

    The REF62xx family of voltage references have an integrated low output impedance buffer; therefore, there is no need for an external buffer while driving the REF pin of an high voltage reference DAC. So, i expect the total noise of the REF6225 is higher than the REF7025. Is it correct?

    Finally, which of the 2 devices recommended to drive the DAC81404?

    I would recommend REF70. REF70 has much better noise from 0.1Hz to 1kHz when compared to REF6225. It is extremely difficult to filter out noise from 0.1Hz to 10Hz. It is much easier to filter out higher frequency noise, if needed. For this reason, I would recommend REF7025QFKHT or REF7025QDGKR. If a buffer is desired, I would recommend a device like OPA196.

    Please let me know if there are any other questions.

    Thanks,

    Jackson

  • 0 in reply to Jackson Wightman
    Prodigy 210 points

    Hi Jackson,

    thank you for the answer.

    So the REF7025 is recommended to use with DAC81404. But, about the the buffer like OPA196, is it necessary to use it?

    I noticed another very interesting component: the REF54250. It has a low frequency noise of 0.11 ppm with a capacitor C_NR=100 uF (see page 6 anf Figure 7-9 of the datasheet).

    Do you think it can be used instead of the REF7025? Is it necessary to use an external buffer?

    Thank you in advance.

    Best Regards,

    Matteo Ricci

  • 0 in reply to Matteo Ricci
    TI__Expert 7910 points

    Hi Matteo,

    A buffer is likely not necessary because DAC81404 has an internal reference buffer seen here:

    Both REF54 and REF70 are great options to use with DAC81404. Another option is REF50E, which also has the C_NR feature. Here is a quick comparison between the devices:

    1. REF54250CDR (plastic SOIC package) https://www.ti.com/product/REF54 

    • 0.8 ppm/°C temperature drift from 0°C to 70°C
    • 0.45 ppm p-p noise, 0.11 ppm p-p noise with C_NR = 100µF. Please keep in mind that using C_NR increases the startup time.
    • 25 ppm long-term drift for the first 1000 hours

    2. REF7025QDGKR (plastic VSSOP package) https://www.ti.com/product/REF70 

    • 2 ppm/°C temperature drift from -40°C to 125°C
    • 0.23 ppm p-p noise
    • 75 ppm long-term drift for first 1000 hours
    • Ceramic package also available for improved long-term drift of 35 ppm for the first 1000 hours

    3. REF5025EIDR (plastic SOIC package) https://www.ti.com/product/REF5025/part-details/PREF5025EIDR 

    • 2.5 ppm/°C temperature drift from -40°C to 125°C
    • 0.5 ppm p-p noise. Also has C_NR feature
    • 25 ppm long-term drift for first 1000 hours

    Please let me know if there are any other questions.

    Thanks,

    Jackson

  • 0 in reply to Jackson Wightman
    Prodigy 210 points

    Hi Jackson,

    thank you thanks for the detailed answer.

    I will use the REF5425.

    Best Regards,

    Matteo Ricci