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Why does TI LM57 analog temp sensor(connected to MSP430 ADC) have slow ramp up ???

Vern Yip
Intellectual 810 points
Other Parts Discussed in Thread: LM57, MSP430F5310

Hi Everyone


I have a strange issue with using the TI MSP430F5310 ADC and the TI LM57 temp sensor.  the Rsense values are at 46.4k and 499.9k for Rsense1/Rsense2. 


The issue is that, when my device(board) is first powered on, the LM57 reports a very low reading.  Then while my debug-board is doing nothing, eventually, the LM57 will hit steady state maybe 2-3 minutes and report atleast 7 degrees (C) higher. 


Does anyone know if this is typical characteristics of the LM57 temperature sensor having to ramp up when power is applied? 


My debug board is also using two other sensors: CAT34TS02 but they are digital (no resistors) and use I2C for commuication.  These temp sensors don't seem to have any ramp up issues.

Once the steady state has been reached with LM57 and CAT34TS02, they seem to respond correctly because the starting temperature and ending temperature (after some processing), shows that they are still 5-6 degrees difference apart from start to finish.

Thanks

  • 0
    TI__Expert 7220 points

    Hi Vern,

    Can you please provide a schematic and layout of your board?

    -Michael Wong

  • 0 in reply to Michael Wong
    Intellectual 810 points

    Hi There


    Unfortunately, I cannot post any schematic or describe in any more detail as this is a company proprietary device.  Just wanted to see if this issue is a known issue. 


    I have since confirmed that it is not an my ADC math calculation problem.  In fact, the register ADC10MEM0 data that I read back from the ADC does decrease (10-bit value of 430 down to 410) when the sensor ramps up.  So it is definitely coming from the sensor or ADC.

    I have also tried multiple devices and it is the same thing.

  • 0 in reply to Vern Yip
    TI__Expert 7220 points

    Hi Vern,

    You do not have to give me the full schematic, just part of the schematic with the LM57 would be fine.

    But if you cannot give that out then help me answer these questions so I can try to debug this problem:

    1. How is the LM57 connected to the MSP430F5310? Is there anything connected between the two parts?

    2. How is the LM57 connected to power and ground? Is there a power and ground plane involved?

    -Michael Wong