• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 16 subscribers
  • Views 1868 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

SN74CBT3251: leakage current ?

Thomas LE BIVIC
Intellectual 510 points
Part Number: SN74CBT3251

Hi, 

I'd like to test several resistive sensors versus temperature. Outside of the climatic chamber I'll have a board (Arduino driven) that will switch the precision ampermeter to each sensor.

The only issue I see is the leakage current of the chosen multiplexer: SN74CBT3251. The only figure related I found in datasheet is Ii=+/-1µA max. I'm not sure of what it means.

In my setup I'll have:

- on common pin: a voltage generator of 1V

- on each output of the multiplexer: a sensor of about 1Mohm.

Actually, the setup is differential, so it's the same on the other side of the sensor exept the common pin is connected to the return of the voltage generator.

 What should I expect as measurement error in this setup? If there is 1µA on each "off" output and 1µA (1V/1Mohm) on my "on" input it does'nt sounds good :/

But there is still a chance to keep this setup as my only concern is relative measurement so if the leakage is independant of the output load it should be ok. Is it?

Last question: How variable is the leakage current from one output to the other? Maybe I can, measure with a precision 1Mohm and then juste calibrate the error?

Any suggestion is welcome,

Thanks for your help,

Thomas

  • 0
    TI__Expert 3180 points

    Hello Thomas,

    To answer the first question, leakage is independent of the current which can be caused by your load. With that being said, the spec that we have on there is that leakage can be as high as 1uA. It can also be much lower.

    There are two types of leakage currents, leakage when the switch is on or leakage when the switch is off.

    Based on the description of your set up, it looks like you are concerned about the effects that on leakage will have on your system with a 1MOhm load while that switch is on, is this correct?

    Please see below for additional information about how leakage current works/behaves:

    Thank you,

    Louie

  • 0 in reply to Louie
    Intellectual 510 points
    Hello Louie,

    Thank you for your answer (didn't get notified sorry for the delay),

    The goal is to measure sensors resistance so, to me, off leakage will be as anoying as on leakage (because when one is on seven are off ^^). But as I'm only concerned about relative evolution when thermal stress is applied, I think it's not an issue here.

    What can I expect from input to input and from chip to chip varation for leakage currents ?

    Have a good day,

    Thomas
  • 0 in reply to Thomas LE BIVIC
    TI__Expert 3180 points

    Hello Thomas,

    I apologize that this took so long for us to get back to you. 

    Please see below of a quick ON leakage measurement I took across a small sample of SN74CBT3251PWR devices (Please keep in mind that TI can not guarantee these values for all devices, this was just what I saw in my small sample from one lot of devices)

    Thank you for your patience,

    Louie