MSP430FR5969: 1.8V Operation

I plan to use the MSP430FR5969 at 1.8V. I have set up a circuit to start at 2V and drop down to 1.8V as required. What do I need to do programmatically (using driverlib) to make this happen? 

I tried using PMM_disableSVSH() then putting it in lpm2, but that didn't seem to work. The program only works for a couple of seconds and then stops. 

CODE SNIPPET: 

#define P1 GPIO_PORT_P2, GPIO_PIN2
#define P2 GPIO_PORT_P1, GPIO_PIN5

void main (void)
{
WDT_A_hold(WDT_A_BASE);

GPIO_setAsOutputPin(P1);
GPIO_setAsOutputPin(P2);
GPIO_setAsPeripheralModuleFunctionInputPin( GPIO_PORT_PJ,GPIO_PIN4 + GPIO_PIN5, GPIO_PRIMARY_MODULE_FUNCTION );
GPIO_setOutputHighOnPin(P2);

PMM_disableSVSH();
PMM_unlockLPM5();

CS_setExternalClockSource(32768,0);//Set external clock frequency to 32.768 KHz
CS_turnOnLFXT(CS_LFXT_DRIVE_0); //Start XT1 with no time out

CS_initClockSignal(CS_ACLK,CS_LFXTCLK_SELECT,CS_CLOCK_DIVIDER_1); //Set ACLK=LFXT

//Start timer in continuous mode sourced by ACLK
Timer_A_clearTimerInterrupt(TIMER_A1_BASE);
Timer_A_initContinuousModeParam param = {0};
param.clockSource = TIMER_A_CLOCKSOURCE_ACLK;
param.clockSourceDivider = TIMER_A_CLOCKSOURCE_DIVIDER_1;
param.timerInterruptEnable_TAIE = TIMER_A_TAIE_INTERRUPT_ENABLE;
param.timerClear = TIMER_A_DO_CLEAR;
param.startTimer = false;
Timer_A_initContinuousMode(TIMER_A1_BASE, &param);
Timer_A_startCounter(TIMER_A1_BASE,TIMER_A_CONTINUOUS_MODE);

_low_power_mode_2();

}

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=TIMER1_A1_VECTOR
__interrupt
#elif defined(__GNUC__)
__attribute__((interrupt(TIMER1_A1_VECTOR)))
#endif
void TIMER1_A1_ISR (void)
{
switch ( __even_in_range(TA1IV,14) ){
case 0: break; //No interrupt
case 2: break; //CCR1 not used
case 4: break; //CCR2 not used
case 6: break; //CCR3 not used
case 8: break; //CCR4 not used
case 10: break; //CCR5 not used
case 12: break; //CCR6 not used
case 14:
GPIO_toggleOutputOnPin(P1);
break;
default: break;
}
}