How to reduce supply current on MSP430F5528?

Hi All,

On my MSP430F5528 I need to run now a real time clock from a small coin battery. I tried several thing but could not lower drain below 30uA. Even entering LPM4 does not help.

Intended operation is to sleep till USB is connected. Here my code:

      //Only wake up when power is present

      USBKEYPID   =     0x9628;

      USBPWRCTL   |=    VBONIE;  // enable interrupt VBUSon

      USBKEYPID   =         0x9600;

      while(!(USBPWRCTL & USBBGVBV))

      {          

            REFCTL0 = 0x0080;          // Power off external reference

            RTCPS1CTL &= ~(RT1PSIE);   // disable timer interrupt

            P5SEL |= BIT4+BIT5;        // Port select XT1

            UCSCTL6 &= ~XT1OFF;        // XT1 On

            UCSCTL6 |= XCAP_3;         // Internal and external load cap 5.5 ~ 7.5 pF

            UCSCTL4 = 0;               // set to clocks to XT1

            P1OUT = 0;

            P1DIR = 0xFF;

            P2OUT = 0;

            P2DIR = 0xff;

            P3OUT = 0;

            P3DIR = 0xff;

            P4OUT = 0;

            P4DIR = 0xFF;

            P5OUT = 0;

            P5DIR = 0xCF; // Don't touch XT1

            P6OUT = 0;

            P6DIR = 0xFF;

            P6OUT = 0;

            P6DIR = 0xFF;

            PJOUT = 0;

            PJDIR = 0xFF;

            while (SFRIFG1 & OFIFG) {   // check OFIFG fault flag

              UCSCTL7 &= ~(DCOFFG+XT1LFOFFG+XT2OFFG); // Clear OSC fault flags

              SFRIFG1 &= ~OFIFG;        // Clear OFIFG fault flag

            }

            UCSCTL6 &= ~(XT1DRIVE_3);          // XT1 is now stable, reduce drive strength

            _bis_SR_register(LPM4_bits + GIE);

            _nop();

      }

Any sugestions are appeciated.

Regards
Guenther