Hello,
The customer would like to know input impedance when ADS8688A power off. There is I-V curve on Figure 70 in datasheet. Input current seems to limit by internal 1Mohm resister. Does this mean ADS8688A input impedance is approximately 1Mohm?
Do not needed to consider to make the path below? I think typically ESD protection is pin-to-VCC or GND-to-pin diode.
Input voltage source -> input pin -> ESD protection
Best regards,
Toshihiro Watanabe
Hello Toshihiro,
The input impedance of ADS8688A is constant and resistive, 1Mohm on each channel. The Electrical Characteristics in page 6 of ADS8688A datasheet and the input circuit below have shown it.
The ESD protection on this ADC is a SCR-Based protection structure. The structure to use a simple ESD diode between AVDD and GND for protection as you mentioned is impossible to be used for ADS8688A because the input range on ADS8688A is larger than the power supply, this is the key benefit to use SCR-based protection structure. The TI Precision Labs ADC - Electrical Overstress on Data Converters has covered this kind of information. Also, the training materials and videos explain how to interoperate the absolute maximum specifications and provide circuit design techniques that protect against EOS damage and have minimal impact on system performance.
Thanks®ards,
Dale
