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MSPM0C1104: Low power optimization - ADC pulls current high

R H
Prodigy 60 points

Part Number: MSPM0C1104

I tried optimizing the power consumption of my device and can get as low as ~4.5uA on my custom hardware in STANDBY1. When requesting a short ADC measurement. however, my current consumption jumps to over 1mA. I did narrow it down to a snippet where I shortly initialise my ADC and start the conversion, then after the conversion stop it again.

This is roughly what my low power mode initialisation does.

DL_TimerA_stopCounter(PWM_INST);
DL_TimerA_disablePower(PWM_INST);

DL_I2C_disableController(I2C_0_INST);
DL_I2C_disablePower(I2C_0_INST);

DL_VREF_disableInternalRef(VREF);
DL_VREF_disablePower(VREF);
DL_ADC12_disableConversions(ADC12_INST);
DL_ADC12_disablePower(ADC12_INST);

delay_cycles(POWER_STARTUP_DELAY);

 

This is my problematic code. Inserting a delay_cycles with ~300us or more wait time fixes the issue.

void adc_off(void) {
    DL_VREF_disableInternalRef(VREF);
    DL_VREF_disablePower(VREF);
    DL_ADC12_disableConversions(ADC12_INST);
    DL_ADC12_disablePower(ADC12_INST);
    delay_cycles(POWER_STARTUP_DELAY);
}

void adc_on(void){
    DL_VREF_enablePower(VREF);
    DL_VREF_enableInternalRef(VREF);
    DL_ADC12_enablePower(ADC12_INST);
    DL_ADC12_setStartAddress(ADC12_INST, DL_ADC12_SEQ_START_ADDR_00); // manual repeat of ADC sequence
    DL_ADC12_enableConversions(ADC12_INST);
    DL_ADC12_startConversion(ADC12_INST);
    delay_cycles(POWER_STARTUP_DELAY);
}

void my_conversion(void) {
    adc_on();
    while (interrupt_received == false) {;}
    delay_cycles(24*100*3); // fixes issue
    adc_off();
}

Why exactly could this occur? Why does a delay annul this issue? Why 300us? The time seems quite long to me for a 24MHz device.

When I remove the while loop and the delay, the issue also doesn't occur (no optimization). In that case, however, I assume that the registers have not been processed before turning ADC off again.

CTL0 = 0x05000000
CTL1 = 0x00010000
CTL2 = 0x03000000

  • 0
    TI__Genius 13970 points

    Hello RH,

    I want to check some details about this issue:

    • It is normal that the current up when CPU and ADC is involved in to do conversion and calculation, etc.
    • The current you measured is the instantaneous value or the average value in a long time?
    • I think you use ADC interrupt to receive the ADC conversion result, right? So you need CPU involved in this process.
    • It is very strange that after you add a time delay, the power consumption down, because in the time length you do the time delay, the CPU is wake and ADC is also powered up. So I can't understand why the power consumption actually decreased.

    BR,

    Janz Bai

  • 0 in reply to Janz Bai
    Prodigy 60 points

    Hello Janz Bai,

    The 1mA current stays for an indefinite period of time but may be resolved with new ADC measurements it seems.
    Yes, I am using ADC interrupts to notify my task of new available data.

    I actually might have found a clue. It might be that I am disabling the ADC while a measurement is running. But would the ADC power down not resolve this? My ADC conversion runs for about 100us.

    Best Regards,

    RH

  • 0 in reply to R H
    Prodigy 60 points

    I should add that my ADC conversion runs as a sequence with 4 total conversions.

    Adding stopConversion() at the top of my adc_off() function did nothing.

  • 0 in reply to R H
    TI__Genius 13970 points

    Hello RH,

    Could you please help to explain what is the meaning of "I am disabling the ADC while a measurement is running"?

    You can try to reset whole ADC module before enter STANDBY mode, and then re-initialize ADC again after exit from STANDBY mode 

    And by the way, could you please show the ADC interrupt handle part code to me too? I want to check the interrupt handler setting when you use sequence

    BR,

    Janz Bai

  • 0 in reply to Janz Bai
    Prodigy 60 points

    Hello Janz Bai,

    by disabling the ADC I mean the adc_off function I posted initially. I am starting the measurement, wait for the interrupt to notify me that my measurement is done, then call adc_off. This could potentially happen during the measurement of the second measurement in the sequence.

    volatile interrupt_received = false;

void ADC12_INST_IRQHandler(void)
{
    switch (DL_ADC12_getPendingInterrupt(ADC12_INST))
    {
    case DL_ADC12_IIDX_MEM0_RESULT_LOADED:
        interrupt_received = true;
        adc_data_flags |= 0x1;
        break;
    case DL_ADC12_IIDX_MEM1_RESULT_LOADED:
        adc_data_flags |= 0x2;
        break;
    case DL_ADC12_IIDX_MEM2_RESULT_LOADED:
        adc_data_flags |= 0x4;
        break;
    case DL_ADC12_IIDX_MEM3_RESULT_LOADED:
        adc_data_flags |= 0x8;
        DL_ADC12_stopConversion(ADC12_INST);
        DL_ADC12_setStartAddress(ADC12_INST, DL_ADC12_SEQ_START_ADDR_00); // manual repeat of ADC sequence
        break;
    default:
        break;
    }
}

    12-bit ADC, no averaging, measuring on channel 2 of the SOT-16 (DYY) package. Using ULPCLK at 24MHz, 24 clock divider. Software triggers, internal VRef at 1.4V. 

    Best Regards