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LM95235 use with single ended diode

EngH060
Intellectual 365 points
Other Parts Discussed in Thread: LM95235, TMP411, TMP431, TMP432

Looking to use the LM95235 with a processor with an internal thermal diode.  With this processor however the diode cathode is connected to GND as opposed to how internal thermal diodes are often connected.

Can you confirm if the LM95235 is suitable for use with a remote diode connected in this fashion?  If not, can you recommend a more suitable part?

  • 0
    TI__Guru 71526 points

    Page 25 in the datasheet, relating to Eq (4) states that the processor diode/xstr can be connected to GND, with a result of "non-ideality spread".  Fig 18 does not actually show the collector connected to GND, but the text describes it.  >  When this “diode” equation is applied to an integrated diode such as a processor transistor with its collector tied to GND as shown in Figure 18 it will yield a wide non-ideality spread.

    If you need SMBus interface, you could use something like the TMP411, which does show the processor sensor connection to GND (page 1) and page 6 FIg 11.  www.ti.com/product/tmp411 .

    -Leonard

    ACAT Dallas

  • 0
    TI__Guru 71526 points

    Here is a previous E2E post that shows how to connect the sensor when D- is connected to GND: http://e2e.ti.com/support/other_analog/temperature_sensors/f/243/p/146976/534047.aspx#534047 .

  • 0 in reply to LeonardEllis
    TI__Mastermind 32290 points

    Hi Leonard,

    I would like to clarify that there aren’t devices supported the D- pin connected to GND in SVA-ISC product line. Most of the digital temperature sensors sense the temperature of a remote diode integrated in another IC such as processor, ASIC, or FPGA. It’s usually a PNP transistor with its collector tied to GND. That’s what we wrote in the datasheet.

    In addition, it can sense the diode-model using the MMBT3904 transistor as shown in figure 18 of the LM95235 datasheet. The LM95235 has a TruTherm BJT/Transistor beta-compensation where it can be programmed to select the diode-model between a typical Intel processor or MMBT3904 transistor.

    The digital temperature sensors require monitoring the voltage across the diode via D+ and D- pins; therefore, the above diagram will not suitable for LM95235.

    Please let me know if you have further question.

    Aaron

  • 0 in reply to Aaron Heng
    TI__Guru 71526 points

    Thanks Aaron,

      Just to clarify, you're saying the configuration shown in the initial post on this query, there are no temp sensors in our product portfolio, LMxxx or TMPxxx, that can support this type of configuration?

    Eng - please provide the processor type so we can research a recommended usage for the temp diode.

    -Leonard

     

  • 0 in reply to LeonardEllis
    TI__Mastermind 32290 points

    Hi Leonard,

    I am spoken for the LMxxx. You need to confirm with Abhi in AIP for the TMPxxx. It seems that your previous posted that linked to Ian William's response. That's might be doable, but I think you should confirm with him. In the past, I have tried with a diode, and I didn't get a good result.

    Aaron

  • 0 in reply to LeonardEllis
    Intellectual 365 points

    Further application details and the processor specifics:  The chip in this application is the Vitesse VSC7432.  The cathode side is internally connected to VSS in the device.  Looking  for an I2C interface,   -40 – +85C operation at 3.3V  perferred.

    Any suitable recommendations would be appreciated.

     

  • 0 in reply to EngH060
    TI__Expert 7945 points

    Hello,

    You can use any of our TMP4XX devices (TMP431,TMP411,TMP432 etc) with remote channel configuration and have it working by using the above configuration. Measuring internal IC temperature by using one if its internal diodes is a pretty common practice although it may not be very accurate when ompared to using a BJT as diode configuration because of n-factor correction like in this post here:

    http://e2e.ti.com/support/other_analog/temperature_sensors/f/243/p/146976/534047.aspx#5340474

    Hope I answered your question.

    Best Regards,

    Abhi