• State Resolved
  • Locked Locked
  • Replies 10 replies
  • Answers 1 answer
  • Subscribers 31 subscribers
  • Views 1246 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.

LM335A: LM335A

Mark Stern
Intellectual 285 points
Part Number: LM335A
Other Parts Discussed in Thread: LMT01, TMP117, TMP107, TMP112, LM335

What is the maximum load capacitance for the LM335A?

  • 0
    TI__Expert 6475 points

    Stern,

    There isn't a max capacitance load limit in the datasheet. However, I don't think capacitive load is an issue for the device since its output stage is just the zener output + resistor.

    -Kelvin

  • 0 in reply to Kelvin Le THS
    Intellectual 285 points
    Dear Kelvin:

    On page 8, Section 7.2, the Functional Block Diagram shows an active circuit with internal feedback which leads me to believe it may be affected by an external capacitor. Note that none of the application circuits show any capacitive loading.

    Is there a paper on this? I recall seeing this question posed to Bob Pease years ago but have no idea how to locate his response.

    Regards,

    Mark
  • 0 in reply to Mark Stern
    TI__Expert 6475 points
    Mark,

    Let me contact the design team to clarify.

    -Kelvin
  • 0 in reply to Kelvin Le THS
    TI__Expert 6475 points
    Mark,

    What is the maximum capacitive load specification you are targeting for the application?

    -Kelvin
  • 0 in reply to Kelvin Le THS
    Intellectual 285 points

    Dear Kelvin:

    Less than the allowed maximum.

    Perhaps there is a chart of series resistance vs. capacitive load for stability?

    Regards,

    Mark

  • 0 in reply to Mark Stern
    TI__Expert 6475 points
    Mark,

    This is an old National device and thus the design team has trouble accessing the design files. Our designer would like to know what capacitive load you intent to use so he could simulate the behavior based on the schematic shown in the datasheet.

    May I ask what application is this for? What are your system requirements? Accuracy? Form factor?

    Are you open to using a digital temperature sensor? The system accuracy is guaranteed. You don't need to calibrate to get the guaranteed accuracy.


    -Kelvin
  • 0 in reply to Kelvin Le THS
    Intellectual 285 points

    Dear Kelvin:

    I am using the die version of this device, LM335A MDC.

    I will provide filtering into an ADC.

    Is it OK to simply add, for example, a 0.1uF (or other) cap across the output or is a resistor in series with the cap advisable?

    If the unit is at the end of a cable, is this a problem?

    Any guidance concerning stability criteria would be welcome.

    Regards,

    Mark

  • 0 in reply to Mark Stern
    TI__Expert 6475 points

    Mark,

    I will forward the information to our designer.

    For any analog signal chain, you will have to consider noise interference. Especially for a long cable. The solution for these types of problems are not unique to analog temperature sensors. Generally, you want to shield and limit bandwidth by filtering, which can be costly. Thus, that's why I proposed that you should consider our digital sensors like TMP117/TMP112/LMT01/TMP107.
    Are you making a probe?

    -Kelvin

  • 0 in reply to Kelvin Le THS
    TI__Expert 6475 points

    Mark,

    Please refer to pg. 32 for Bob Pease's comment on LM335.  He basically said that 0.1uF+22ohm is fine.  The article also pointed out a way to validate the stability empirically if you're interested in other cap values.

    Bob Pease Lab Notes Part 7.pdf

    Unfortunately, since this is an old part we can't simulate the original design to give you a general recommendation of capacitive load vs isolation resistor requirement.  Your best course of action forward is by empirically testing the stability of the circuit as describe in Bob's article. 

    -Kelvin

  • 0 in reply to Kelvin Le THS
    Intellectual 285 points
    Dear Kelvin:

    Thanks for Bob's article.

    Regards,

    Mark