MSP430I2021: Integrated temperature sensor value calculation

Hello Nicolas,

You can find a C code example in MSP430Ware that uses the integrated temp sensor in the i20xx devices. The project name is "msp430i20xx_sd24_06". Be sure to follow the notes about capacitor between Vref and AVss and also ensuring the 'low_level_init.c' file is included with the project when building/running the example.

With regards to which equation to use, I think you'll find the comments at the top of the code example mentioned above to be very helpful. Using these equations, you could assume an offset of zero initially and then characterize the performance of the internal temperature sensor over the desired temperature range. Then, based on this performance (observed versus actual), you can then introduce an offset. If this offset varies for certain ranges within your overall temp range, you could use offsets specific to those ranges.

msp430i20xx_sd24_06.c

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//******************************************************************************
//  MSP430i20xx Demo - SD24, Using the Integrated Temperature Sensor
//
//  Description: This program uses the SD24 module to perform a single
//  conversion on a single channel which is internally connected to the SD24's
//  temperature sensor. Once the conversion is completed, the result is stored in
//  a variable then converted into Celsius and Fahrenheit values.
//
//  Test by setting a breakpoint at the indicated line. Upon reaching the breakpoint
//  the conversion result will be stored in the results array. The result will
//  then be taken and converted into degrees K, C, and F and be saved in the same
//  array.
//
//  ACLK = 32kHz, MCLK = SMCLK = Calibrated DCO = 16.384MHz, SD_CLK = 1.024MHz
//  * Ensure low_level_init.c is included when building/running this example *
//
//  Notes: For minimum Vcc required for SD24 module - see datasheet
//         100nF cap btw Vref and AVss is recommended when using 1.2V ref
//
//  Sensor's temperature coefficient is 2.158mV/K (from datasheet)
//  Sensor's offset voltage ranges from -100mv to 100mV (assume 0)
//  Vsensor = 1.32mV * DegK + Vsensor_offset (assuming 0mv for offset)
//  Vsensor = (SD24MEM0)/32767 * Vref(mV)
//  DegK = (SD24MEM0 * 1200)/32767/2.158 = (SD24MEM0 * 1200)/70711
//  DegC =  DegK - 273
//  DegF = (DegC * 9/5) + 32
//
//
//               MSP430i20xx
//             -----------------
//         /|\|                |
//          | |                |
//          --|RST             |
//            |                |        (A0.6+/- connected internally)
//            |A0.6+      VREF |---+    (to SD24's temperature sensor)
//            |A0.6-           |   |
//            |                |  -+- 100nF
//            |                |  -+-
//            |                |   |
//            |           AVss |---+
//
//  T. Witt
//  Texas Instruments, Inc
//  September 2013
//  Built with Code Composer Studio v5.5
//******************************************************************************
#include "msp430.h"

unsigned int  results[4];                       // SD24 Conversion and Temp Results
                                                // results[0] = raw SD24 results
                                                // results[1] = temp in K
                                                // results[2] = temp in C
                                                // results[3] = temp in F

void main(void) {
    WDTCTL = WDTPW | WDTHOLD;                   // Stop WDT

    SD24CTL = SD24REFS;                         // Internal ref
    SD24CCTL0  |= SD24SNGL | SD24DF | SD24IE;   // Enable interrupt
    SD24INCTL0 |= SD24INCH_6;                   // Internal temp sensor

    __delay_cycles(3200);                       // Delay ~200us for 1.2V ref to settle

    while(1) {
        SD24CCTL0 |= SD24SC;                    // Set bit to start conversion
        __bis_SR_register(LPM0_bits | GIE);     // Enter LPM0 w/ interrupts
        __no_operation();                       // For debugger

        // Calculate Temperatures in different scales
        results[1] = ((unsigned long)results[0] * 1200)/70711;
        results[2] = results[1] - 273;
        results[3] = (results[2] * 9/5) + 32;

        __no_operation();                       // SET BREAKPOINT HERE
    }
}

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=SD24_VECTOR
__interrupt void SD24_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(SD24_VECTOR))) SD24_ISR (void)
#else
#error Compiler not supported!
#endif
{
    switch (__even_in_range(SD24IV,SD24IV_SD24MEM3)) {
        case SD24IV_NONE: break;
        case SD24IV_SD24OVIFG: break;
        case SD24IV_SD24MEM0:
                   results[0] = SD24MEM0;       // Save CH0 results (clears IFG)
                   break;
        case SD24IV_SD24MEM1: break;
        case SD24IV_SD24MEM2: break;
        case SD24IV_SD24MEM3: break;
        default: break;
    }
    __bic_SR_register_on_exit(LPM0_bits);       // Wake up from LPM0
}

Regards,

James

MSP Customer Applications