I have a few questions with regard to the ADAS3022 device.
1. I would like to add over-voltage protection resistor to each multiplexer input. In order to determine the resistor power dissipation can you provide the
maximum continuous current the multiplexer can tolerate ?
2. If I use the ADAS3022 device at a lower throughput of 100ksps, is it possible to modify the 8Mhz bandwidth of the device for different anti-alias
response and possibly improved noise performance ? Can a single anti-alias filter be added to the AUX input pins to achieve this ?
3. If the AUX pins are not used should they be left floating ?
4. Can this device settle a full-scale step input to 16-bit accuracy within a single conversion for each of the input voltage ranges ?
We are looking into this. I'll get back to you as soon as possible.
I moved this post to the precision ADC community, someone here should be able to help.
Let me address your questions.
1. The maximum continuous current the multiplexer can tolerate is approximately less than 10mA. Note that the violation of absolute maximum ratings (table 4) beyond the datasheet specified limits for a continuous time would also affect the reliability and may cause permanent damage to the device.
2. It’s not possible to modify the 8MHz input bandwidth of the ADAS3022. By adding a single anti-alias filter on the AUX input pins, you cannot improve the noise performance of the other inputs of the device.
3. The ADAS3022 unused AUX input pins should be connected to AGND. Leaving them floating is NOT recommended. They are not sampled unless explicitly called for in the configuration word.
4. This device can settle a full-scale step input to 16-bit accuracy within a single conversion for each of the input voltage ranges except for PGIA gain of 3.2 and 6.4.
Thanks for the feedback.
Can you also provide the input capacitance specification for the analog inputs.
The input capacitance for the ADAS3022 is in the range of 5 pF. Due to the high input impedance amplifiers in front of the SAR ADC, the user will not observe the additional input capacitance of the SAR capacitive DAC used in the conversion process.
I also noticed an inaccuracy in an earlier response. The transient response time specification for the ADAS3022 covers all gain ranges. The ADAS3022 can settle a full-scale step in any gain range within one conversion period. The transient response time specification is 520 nSec as seen on page 4 of the data sheet. This means that once a full-scale step is applied, it will take a maximum of 520 nSec for the device to settle this change in potential.