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