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ADS58B18: ADS58B18

Part Number: ADS58B18

Hi,

In the document "ads58b18.pdf" (SBAS487D - NOVEMBER 2009-REVISED JANUARY 2011):

In the section "ABSOLUTE MAXIMUM RATINGS" on page 2 it says:
"Voltage applied to input pin / INP, INT / MAX / minimum (1.9, AVDD + 0.3)V"
With AVDD = 1.8V, the maximum voltage applied to the input pin equals 1.9V ?

The "ANALOG INPUT" section on page 44 says:
"For a full-scale differential input, each input pin (INP, INM) must swing symmetrically
between VCM + 0.375V and VCM – 0.375V"
With VCM = 1.7V - the voltage applied to the input in the range of 1.325-2.075V.

This does not correspond to the information from "ABSOLUTE MAXIMUM RATINGS".

Help me understand where I'm wrong.

Thank you,
Alpatov Sergey.

  • Hi Alpatov,

    The absolute maximum rating of INM and INP considers some of the worst case scenario when AVDD power is not applied.

    If AVDD power is not applied, then absolute maximum of INM and INP are limited to 1.9V

    As AVDD starts to ramp up, you may apply more input power to the INM and INP pin (i.e. AVDD + 0.3V being maximum). With AVDD being settled at 1.8V, the absolute maximum becomes 1.8 + 0.3V = 2.1V.

    Keep in mind always consider the minimum of the two options.

    -Kang
  • Thank you.
    Ok, I understand your answer.
    Please tell me something else on the topic:
    The operating voltage at theINP and INM inputs is up to 2.075V (see my first question), and the maximum allowable voltage is 2.1V. Such a close location is very very very very very strange.
    In the world there are no protection devices that pass 2.075V and limit above 2.100V.
    There may be a typo in the document: not the "AVDD" but the "AVDD_BUF" ? (which equals 3.3V)
    With respect, Sergey.
  • Sergey,

    I will have to double check with the team and get back to you.

    -Kang

  • Hi Sergey,

    Design team responded back and agrees with your concern. The absolute max should be

    Min(AVDD_BUF+0.3, 3.0)

    Someone on the team will follow up on the datasheet change.

    -Kang

  • Thank you.
    If you plan to edit this document:
    On page 25, the third line above "0000 = 0dB gain (default after reset)" is not valid.
    Experimentally verified: 0101 = 0dB gain.
    But what default after resets - I unfortunately do not remember.
    I wish you every success in your work.
    Best regards, Sergei.