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MSP430G2553: Hardware design to optimize the msp430g2553 consumption

FranMartin
Intellectual 600 points

Part Number: MSP430G2553

Hello,

I am designing a PCB where I will use the msp430G2553. As for the SW, the microcontroller will practically always be in the LPM0 mode and configured with the DCO at 1MHZ. The non - rechargeable lithium battery is used as the power source: (cellpacksolutions.co.uk/.../saft-lsh20-technical-data-sheet.pdf). In the msp430g2553 datasheet, on page 22, the consumption at Vcc = 2.2V is 56uA (I measured it is 42uA) but I could not find the consumption for Vcc = 3.6V in the LPM0 mode, so I have measured it, 77 uA. With these values, is it worth using a LDO about Vout=2.2 with low quiescent current to optimize the consumption of the battery?

Thanks in advance.

Fran.

  • 0
    TI__Genius 15370 points
    Hi Fran,

    It depends on what kind of battery life you want. Using an LDO with Vout = 2.2V will certainly give you longer battery life. You could also go into a deeper low power mode such as LPM2, 3, or 4. But you need to ensure that the low power mode you choose doesn't affect your application (e.g. deactivating a necessary clock source). Overall, if you're running off a battery and concerned about battery life, you'll want to run at the lowest voltage possible and the highest LPM possible.

    Best regards,
    Caleb Overbay
  • 0 in reply to Caleb Overbay
    Intellectual 600 points

    Hi, thanks Caleb Overbay for your response. In principle the microcontroller must work in the LPM0 mode because I need to make measurements periodically and I do not know how to correctly design the PCB to add an external oscillator crystal. So, my question is if assuming the LPM0 mode, if I use an LDO with Vout = 2.2 V with a quiescent current maximum of 10 uA (for example), the consumption would be 42 uA (56 uA by datasheet) + 10 uA = 52 uA (or 66 uA). So, if I have measured the consumption at 3.6 V and it is 77 uA, the saving of consumption is low or I have been wrong in the way of estimating it? Thank you.

  • 0 in reply to FranMartin
    TI__Genius 15370 points

    Hi Fran,

    You're correct. In the scenario you've described above you would only save ~10uA. The biggest benefit would be to enter LPM3 and use a 32 kHz crystal to run a timer and wake the device periodically. If you're concerned about implementation, I recommend taking a look at MSP430 32-kHz Crystal Oscillators which describes in full how to setup a crystal oscillator and design a PCB layout with a crystal in mind.

    Best regards,

    Caleb Overbay

  • 0 in reply to Caleb Overbay
    Intellectual 600 points
    Thanks again Caleb Overbay.
    I read that document but I did not understand because in the msp430g2553 launchpad, there are two resistors, R28 and R29. The two terminals of R29 are connected to the XOUT pin and the two terminals of R28 are connected to the XIN pin. Therefore, both resistors are connected in parallel with 0 ohms. Why?
    To design my PCB, is it necessary only the capacitors (following the design criteria of the document) or is it necessary also these two resistors? If this information is in another post I would appreciate if you would pass the link or if you think it is necessary, I start another post for this question.

    Best regards,

    Fran Martin
  • 0 in reply to FranMartin
    TI__Genius 15370 points
    Hi Fran,

    These resistors are in series with the J2 header and the XOUT/XIN pins of the MSP430G2553. They are there simply for the userto be able to access the XOUT/XIN pins when not using them for a crystal. If the user is using these pins for a crystal it is safe to remove R28 and R29.

    So for your PCB you do not need these resistors and should follow the design criteria specified in the document I previously linked to. No need to start a separate post as these questions are all related to achieving the lowest possible power on the MSP430.

    Best regards,
    Caleb Overbay
  • 0 in reply to Caleb Overbay
    Intellectual 600 points
    You've solved all my doubts, Caleb. Thanks for your time.

    Best regards,

    Fran.

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