• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 16 subscribers
  • Views 267 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.

Original question:

TS3A24159: The accuracy of internal resistance on TS3A24159

TS3A24159: Ron Variation Between Switch Channels

Dakshina Shakya
Prodigy 35 points

Part Number: TS3A24159

Tool/software:

Hello, I have an application where a pair of analog switches (TS3A24159) are used as a multiplexer to connect two individual 3-Wire PT100 RTD probes to a single RTD-to-Digital Converter. These RTDs are standard class A units. I'm switching between the two RTDs once every 500ms and I'm reading a difference of ~1.5-2 °C between the two probes. The difference gets worse when the PCB is heating up.

What could be the cause here? Is it the Ron variation on the switch channels causing the issue? 

  • 0
    TI__Mastermind 35648 points

    Hi Dakshina,

    The RON variation is 0.2ohms max across the full -40 to 85C range and the varation is about the same if you look at figure 6-1 for RON across temp at 1.65V supply (worse case). They would likely both be experiencing the same temperature increase though so that would nearly cancel out the variation between the channels. I'm not convinced that 0.2ohm max would cause a discrepancy. It could be the traces themselves. 
    I'm making assumptions here that we can verify that the probes are supposed to be the exact same temperature. Can you maybe try and even switch the channels the probes are on and see if it follows the probe or the channels? Every component on the board will be affected by temperature including the board itself so it may be a little tricky to narrow down but the mux has a fairly consistent RON (unless of course I'm mistaken and 0.2ohm can translate to 1.5C difference, in which case maybe it is the mux).

    Thanks,
    Rami

  • 0 in reply to Rami Mooti1
    Prodigy 35 points

    Thank you so much for the explanation. I understand the full range of variation is not enough to make the difference that we are observing. Will look into the rest of the circuitry to eliminate any stray conductance.