• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 893 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADC128S102: Differences in 5962-07227 and ADC128S102 input impedance

Carolyn Sleeper
Intellectual 280 points
Part Number: ADC128S102

I need to understand the difference in the 5962-07227 and ADC128S102 input impedance.

We are currently using both parts in a similar application. We have noticed a difference between them.

Thanks,


Carolyn Sleeper

  • 0
    TI__Guru**** 180961 points
    Hi Carolyn,

    It is quite possible that the rad hardened version of the ADC128S102 might have some additional filtering for SEL conditions, give us a few days to try and find the detail for you. In the meantime, can you describe what you see on your end?
  • 0 in reply to Tom Hendrick
    Intellectual 280 points
    We measure different impedances DGND and AGND between the commercial part and the space grade part. So we wonder how these grounds are connected internally. Also, since we are using multiple converters in several locations we did not feel that we could connect these grounds together at each converter and instead used a single ground. We have had a part damaged in this configuration and we wonder if this could be a consequence of not tying each set of ground pins together. The damage resulted in a short from VD to both ground pins.
  • 0 in reply to Carolyn Sleeper
    TI__Guru**** 180961 points

    Hi Carolyn,

    I'm sorry for the delay here. I can't find any physical difference between the regular ADC128S102 and the ADC128S102QML-SP besides the ceramic packaging and the additional testing that is done on these RAD Hardened devices. Part of that testing includes an annealing process which could account for the differences you see in the impedance between the AGND and DGND pins. In general though both versions start from the same silicon. The typical application for these parts does tie AGND and DGND together at the chip. If the difference in AGND and DGND potentials exceeds 300mV, you can run the risk of damaging the devices.

  • 0 in reply to Tom Hendrick
    Intellectual 280 points

    Tom,

    Are the grounds tied directly or is there a device between them? Are they a copper short or is there something else between them that ties them together?

    If so , could you describe what is there?

    Thanks,


    Carolyn

  • 0 in reply to Carolyn Sleeper
    TI__Guru**** 180961 points
    Hi Carolyn,

    On the PCB, they are usually tied directly or through a zero ohm resistor. It really depends on how your PCB software and design database are setup. If you define AGND and DGND as two separate nets, the easiest thing to do is add a zero ohm resistor between the two and use seperate analog and digital ground planes. If you defined AGND and DGND as a single net, you can still route the analog and digital signals away from each other and then use a single ground plane that basically isolates the AGND and DGND sides from each other.