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Question regarding using LTC2997 to measure temperature on SoC with remote PNP diode


Is I1 and I2 for LTC2997 variable or fixed? This part appears to be designed to interface with a 3904 diode. When the remote diode is a built into and SoC/FPGA, it may not be able to handle large I1 and I2 because of the size of the diode. Additionally, having higher currents can move the force the diode in be in region where the ideality factor is not 1. Is the Ideality Factor correction intended to be done as a 'post processing' step?



  • Hi,

    Apologies for missing this. LTC2997 is perfectly suited to measure temperature of an FPGA or microprocessor.  The LTC2997 sends measurement currents to the temperature monitoring diode of the FPGA or microprocessor and generates a voltage proportional to the temperature of the diode on its VPTAT output. 

    The LTC2997 is factory calibrated for an ideality factor of 1.004, which is typical of the popular MMBT3904 NPN transistor. Semiconductor purity and wafer-level processing intrinsically limit device-to-device variation, making these devices interchangeable between most manufacturers with a temperature error of typically less than 0.5°C. 

    We do not recommend to use a remote sensing devices with ideality factors higher than 1.004 which in most cases a discrete two terminal diodes. 



  • Hi Mae,

    Thanks for responding back. So in the context of using this to measure the temperature of FPGA or microprocessor,

    1. What are the values of the I1 and I1, the currents forces into the the remote diode located on the FPGA or Microprocessor?

    2. If the Ideality Factor of the remote diode is determined to be different than 1.004 through SPICE simulations, does LTC2997 provide a built-in correction capability?