MSP430G2553, VeREF+ drops voltage after several minutes..

Hi,

I have the chip in my board all works fine exept the VeREF+ issue. I have 3V3 on my board to supply the most peripheral and the MCU and 5V0 to supply one sensor. I use VeREF+(P1.4) made from the 5V0 devided by two (simple resistor devider 10K/10K). And signal from the sensor devided by two too (another simple resistor devider 10k/10k). All goes fine several minutes, but after i measure VeREF+ from the devider and got values from 1V to 0.5V or even 0.3V, as the 5V0 is stable.

Below is full code with ADC init, measurement and CPU frequency init, I feel that i do something wrong during initialisation, please help:

#include "msp430g2553.h"
//////////////////////////////////////////////////////////////////////
// Definitions
//////////////////////////////////////////////////////////////////////

//
// Constants
//
static const int Nmax = 800; // RH = 100%
static const int Nmin = 164; // RH = 0%

// Define P1 pins
// P1.4 Vcc of RH sensor from devider (use as Vref for ADC)
// P1.3 V from RH sensor from devider
#define rhVccPin       (BIT4)
#define rhSencePin     (BIT3)

// functions
void clockInit(void);        // system clock(s) init
void gpioInit(void);         // initialize ports
void ADC10_Init(void);
unsigned  int    RHMeasurement(void); // max - 1023 (Vcc),
                                        // min - 0 (Vss)
void sleep_msec(unsigned int);//delay
//////////////////////////////////////////////////////////////////////
//      Main
//////////////////////////////////////////////////////////////////////

unsigned  int rhN;
unsigned int RH;
float calc_;
int main( void )
{
  // Stop watchdog timer to prevent time out reset
  WDTCTL = WDTPW + WDTHOLD;
  // Inits
  gpioInit();
  clockInit();
  ADC10_Init();

    // Main forever loop

  for(;;){




    // 1. measure
    rhN = RHMeasurement(); // max - 1023 (Vcc), min - 0 (Vss)

    // 2. calculate
    if (rhN>=Nmax){
      // 100%
      RH = 100;
    }else if(rhN<=Nmin){
      // 0%
      RH = 0;
    }else{
      // 0%..100%
      calc_ = (rhN/6.35)-25;

      RH = (rhN/6.35)-25;
    }


    // 3. sleep
    sleep_msec(20);



  }


  return 0;
}
//////////////////////////////////////////////////////////////////////
//      Functions
//////////////////////////////////////////////////////////////////////
void sleep_msec(unsigned int t){
  TACCR1 = t*2000;                           // ms  when 2MHz sub frequency
  TACCTL1 = CCIE;                           // Compare mode, interrupt
  TACTL = TASSEL_2 + TACLR + ID_0 + MC_2;   // SMCLK, TA clear, continuous mode
  __bis_SR_register(LPM0_bits + GIE);       // Enter LPM0, wait for CCR1 int
}

void gpioInit(void){
    // Initialize I/O pins. First clear all and make them output
    // P1.x
  P1OUT = 0x00;
  P1DIR = 0xFF;
  P1DIR &= ~rhSencePin ;
  P1DIR &= ~rhVccPin;
    // P2.x
  P2OUT = 0x00;
  P2DIR = 0xFF ;

}

void clockInit(void){



    BCSCTL2 = SELM_0 | DIVM_0 | DIVS_3;

    if (CALBC1_16MHZ != 0xFF) {
        /* Adjust this accordingly to your VCC rise time */
        __delay_cycles(100000);

        /* Follow recommended flow. First, clear all DCOx and MODx bits. Then
         * apply new RSELx values. Finally, apply new DCOx and MODx bit values.
         */
        DCOCTL = 0x00;
        BCSCTL1 = CALBC1_16MHZ;     /* Set DCO to 16MHz */
        DCOCTL = CALDCO_16MHZ;
    }

    /*
     * Basic Clock System Control 1
     *
     * XT2OFF -- Disable XT2CLK
     * ~XTS -- Low Frequency
     * DIVA_0 -- Divide by 1
     *
     * Note: ~XTS indicates that XTS has value zero
     */
    BCSCTL1 |= XT2OFF | DIVA_0;

    /*
     * Basic Clock System Control 3
     *
     * XT2S_0 -- 0.4 - 1 MHz
     * LFXT1S_0 -- If XTS = 0, XT1 = 32768kHz Crystal ; If XTS = 1, XT1 = 0.4 - 1-MHz crystal or resonator
     * XCAP_1 -- ~6 pF
     */
    BCSCTL3 = XT2S_0 | LFXT1S_0 | XCAP_1;

}

// Measure count value for light: max - 1023 (Vcc), min - 0 (Vss)
unsigned  int  RHMeasurement(void)
{
  unsigned int result;

  ADC10CTL0 |= ENC + ADC10SC;             // Sampling and conversion start
  __bis_SR_register(LPM0_bits + GIE);        // LPM0, ADC10_ISR will force exit


  result = ADC10MEM;
  return(result);
 }


void ADC10_Init(void)
{
   ADC10CTL0 &= ~ENC;

    /*
     * Control Register 0
     *
     * ~ADC10SC -- No conversion
     * ~ENC -- Disable ADC
     * ~ADC10IFG -- Clear ADC interrupt flag
     * ADC10IE -- Enable ADC interrupt
     * ADC10ON -- Switch On ADC10
     * ~REFON -- Disable ADC reference generator
     * ~REF2_5V -- Set reference voltage generator = 1.5V
     * ~MSC -- Disable multiple sample and conversion
     * ~REFBURST -- Reference buffer on continuously
     * ~REFOUT -- Reference output off
     * ADC10SR -- Reference buffer supports up to ~50 ksps
     * ADC10SHT_0 -- 4 x ADC10CLKs
     * SREF_3 -- VR+ = Buffered VeREF+ and VR- = VSS
     *
     * Note: ~<BIT> indicates that <BIT> has value zero
     */
    ADC10CTL0 = ADC10IE | ADC10ON | ADC10SHT_0 | SREF_3;

    /*
     * Control Register 1
     *
     * ~ADC10BUSY -- No operation is active
     * CONSEQ_0 -- Single channel single conversion
     * ADC10SSEL_3 -- SMCLK
     * ADC10DIV_7 -- Divide by 8
     * ~ISSH -- Input signal not inverted
     * ~ADC10DF -- ADC10 Data Format as binary
     * SHS_0 -- ADC10SC
     * INCH_3 -- ADC Channel 3
     *
     * Note: ~<BIT> indicates that <BIT> has value zero
     */
    ADC10CTL1 = CONSEQ_0 | ADC10SSEL_3 | ADC10DIV_7 | SHS_0 | INCH_3;

    /* Analog (Input) Enable Control Register 0 */
    ADC10AE0 = 0x18;


    /* enable ADC10 */
    ADC10CTL0 |= ENC;
}

// Timer A1 interrupt service routine
#pragma vector=TIMER0_A1_VECTOR
__interrupt void TIMER0_A1_ISR_HOOK(void)
{
  __bic_SR_register_on_exit(LPM0_bits + GIE);

  CCTL1 &= ~CCIFG;



}

#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR_HOOK(void)
{
     __bic_SR_register_on_exit(LPM0_bits + GIE);        // Clear CPUOFF bit from 0(SR)
}