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ADS8664: An unclear description in datasheet

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Replies: 3

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Part Number: ADS8664

Hi,

In ADS8664 datasheet chapter 7.1, there is an unclear  description as below. please kindly explain what is this 30kΩ stand for? thanks.

  • Hi Yue Tang,

    This has to do with over voltage protection. In the ADS8664 datasheet (www.ti.com/.../ads8664) beginning on page 24, section 8.3.3, there is more detail which should help clear things up for you.

     

    Regards,

    Tom

  • In reply to Tom Hendrick:

    Tom,
    Thanks for the reply. But I still don't get it:
    1. what is "Offers a low Impedance of < 30 kΩ"
    2.Why is 30kΩ,not other value?
  • In reply to Yue TANG:

    Hi Yue Tang,

    The condition 2) states the maximum input rating when AVDD(+5V) is available and the condition 3) states that the maximum input rating when AVDD is not present to the ADC.Since AVDD is applied to internal diodes for over-voltage protection(Figure 68), also the internal PGA provides a attenuation to input signal with RFB and 1Mohm input impedance. The absence of AVDD is similar as a high impedance status and an available AVDD shows a low impedance, the impedance on this node will have an influence on input attenuation. 30kohm is a simulation result as the conditions.

    I hope this is helpful to you.

    Thanks, Tom.

    Best regards,

    Dale

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