MSP430FR2355: Power consumption when MCLK is driven at low frequency in Active Mode

O.H

Mastermind 7170 points

Part Number: MSP430FR2355

Hi experts,

Is there any way to reduce power consumption even more than the following under the condition of Active mode?

[Condition]

Measured by Energy Trace using MSP-EXPFR2355 (in Free Run).
Active mode, 32.768KHz input from external crystal in MCLK.
All other peripherals are not used, and all GPIO pins are in the output direction and output Low.
Execute a while loop in the main function
VCC = 3.3V
No significant difference in results when using VLO or REFO
No difference even if SMCLKOFF=1, SMCLKREQEN=0

#include <msp430.h>
/**
 * main.c
 */
int main(void)
{
	WDTCTL = WDTPW | WDTHOLD;	// stop watchdog timer

    P2SEL1 |= BIT6 + BIT7;                  // P2.0: XOUT; P2.1: XI1

    CSCTL4 = SELMS__XT1CLK;
    CSCTL5 = SMCLKOFF_1;
    CSCTL8 &= ~(SMCLKREQEN_1);

    //  CSCTL4 = SELMS__REFOCLK;
    //  CSCTL5 = DIVM__128;

    P1OUT = 0x00;    P1DIR = 0xff;
    P2OUT = 0x00;    P2DIR = 0xff;
    P3OUT = 0x00;    P3DIR = 0xff;
    P4OUT = 0x00;    P4DIR = 0xff;
    P5OUT = 0x00;    P5DIR = 0xff;
    P6OUT = 0x00;    P6DIR = 0xff;

    PM5CTL0 &= ~LOCKLPM5;

    do
    {
        CSCTL7 &= ~(XT1OFFG | DCOFFG);      // Clear XT1 and DCO fault flag
        SFRIFG1 &= ~OFIFG;
    }while (SFRIFG1 & OFIFG);               // Test oscillator fault flag

	while(1){}

	return 0;
}

I understand that it is not appropriate to run MCLK at low frequency because MSP430 has several LPMs. I would like to check if it is possible to lower the power consumption when MCLK is driven at low frequency (below 32.678kHz) in Active Mode.

Best regards,
O.H

over 4 years ago

0 Xiaodong LI over 4 years ago

TI__Mastermind 25285 points

Hi O.H

as your test using Energy Trace, the current on 32KHz crystal MCLK active mode of FR2355 is ~85uA. I think this current is reasonable

at the same time, I think the current should be lower than this value if you use the lower frequency crystal.

but according the DS of FR2355, the typical frequency of LFXT is 32.768KHz

I think we haven't test the low frequency crystal. that means, we can't guarantee the lower frequency crystal can work normally here.

So, I recommend keep using 32.768KHz crystal and MCLK source divider using CSCTL5.DIVM to reduce MCLK frequency lower.

In this case, the current of active mode should be lower than 85uA.

Thanks!

0 O.H over 4 years ago in reply to Xiaodong LI

Mastermind 7170 points

Hi Xiaodong Li,

Sorry for the delay in replying. Thank you for your reply.

I tried to make 128 division(CSCTL5.DIVM) of MCLK, but it was about 82uA and it did not seem to drop any lower than that. I will consider a configuration that uses LMPx well and lowers the power consumption of the entire system.

Best regards,
O.H

+1 Xiaodong LI over 4 years ago in reply to O.H

TI__Mastermind 25285 points

Hi O.H

Thanks for your feedback!

I think it is normal that the current reducing very slow from 32KHz to 250Hz. Please consider using the LPM mode to achive the lower power consumption :)

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MSP430FR2355: Power consumption when MCLK is driven at low frequency in Active Mode