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ADC working in TMS570LS20216 USB KIT

Bindu Tanguturi
Expert 1180 points

Hi All,

We are using TMS570 processor in aerospace application. We need to perform thermal test on the processor. We are planning to perform thermal test on the TMS570 USB kit as it is having temperature sensor. I need to write small application which sends the most significant 8 bits of the on-board thermocouple input connected to ADSIN8 on the SPI. I have gone through the demo code that is provided with the USB kit. I am using the same ADC code that is available in the USB kit with few updates (removing SCI part).  My understanding is that adc_data structure in the Temp_Sensor_demo() function holds the 8bit value.  Is that correct ?

And also I would like to know the temperature calculation.  Like for say ..25deg Outside temperature - > what is Equivalent Voltage - > what is Equivalent 12 bit value given by ADC.

Please let me know.

Thanks in advance.

  • 0
    TI__Expert 7650 points

    Hello Bindu,

    One thing to consider is that the USB stick design is configured to handle a reduced max current of 500mA as per the USB power spec.  In our demo code for the stick we limit the CPU clock to 100 MHz in order to stay within the supply capability.  A 100MHz configuration clearly would not give you a maximum active power situation.  I'm not clear on your configuration and use-case but thought you should be aware of this if you weren't already.  The HDK (or MDK if 'LS20x device) is designed and supports the max 570 CPU clock of 180 (or 160, respectively).

    Regards,

    Brian

  • 0 in reply to Brian Fortman
    Expert 1180 points

    Thanks for the information.

    I am interested to know about the other questions i asked.

    1) My understanding is that adc_data structure in the Temp_Sensor_demo() function holds the 8bit value.  Is that correct ?

    2)  And also I would like to know the temperature calculation.  Like for say 25deg Outside temperature - > what is Equivalent Voltage - > what is Equivalent 12 bit value given by ADC.

    Thanks in advance.

  • 0 in reply to Bindu Tanguturi
    TI__Expert 7650 points

    Hi Bindu,

    Have you had a chance to look at the MCU demo source code that comes with the kit?

  • 0 in reply to Brian Fortman
    Expert 1180 points

    Yes. I have gone through that code only. My questions are related to that code only. Please provide me the information.

  • 0 in reply to Bindu Tanguturi
    TI__Genius 13810 points

    Bindu Tanguturi said:

    Thanks for the information.

    I am interested to know about the other questions i asked.

    1) My understanding is that adc_data structure in the Temp_Sensor_demo() function holds the 8bit value.  Is that correct ?

    HW: adc_data structure holds both the channel ID (field id) and the 12bit value (field value).

    2)  And also I would like to know the temperature calculation.  Like for say 25deg Outside temperature - > what is Equivalent Voltage - > what is Equivalent 12 bit value given by ADC.

    HW: Suppose the ADC gives you a value as '8c4', type: 1/(log((100*4096/hex2dec('8c4')-100)/100)/4330+1/298)-273 in matlab or type =1/(LOG((100*4096/HEX2DEC("8c4")-100)/100, 2.7182818)/4330+1/298)-273 in microsoft excel will get the temperature value in degrees Celsius.

    Thanks in advance.

  • 0 in reply to Haixiao Weng
    TI__Genius 13810 points

    I forgot to mention one thing:

    Because the temperature resisor is smt soldered on board, it actually measures the board temperature. Therefore, you will observe the temperature goes higher and higher after you power up the USB stick. Example: Room temp 25 c, the USB stick might report 25c at startup and 32c after 30 mininute running (the board get hotter when running application).

    Regards,

    Haixiao

  • 0 in reply to Haixiao Weng
    Expert 1180 points

    Thanks for the information.