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MSP430FR2000: Low power sleep state

Part Number: MSP430FR2000
Other Parts Discussed in Thread: MSP430FR5858, TPS22916, MSP-EXP430FR2311

Hello,

I am planning to wake up a GSM module once in 15 minutes using an MCU connected to a switch. In the remaining time I want my MCU to be extremely low powered. For this minimal application which MCU of MSP430 line is best suitable. I felt it is MSP430FR2000 as it is in FR series and is minimal. If there is a better option kindly suggest.

Regards,

Prudhvi Sagar

  • Hi Prudhvi,

    the MSP430FR2000 is a fine choice for this application. Do you have an I-avg current consumption target for this component, or are you just looking for best possible performance in that regard? I ask because, like most things, there are some cost/performance trade-offs to be made in device selection.

    There are two low power modes that you can use in this application:
    - LPM3 is a low power standby state where you can run a 32kHz clock and wake up from it with full RAM and register retention (10 microsecond wakeup time).
    - LPM3.5 is a power-down state where you can run a 32kHz clock and wake up from it, but RAM and register contents are lost and you actually go through a reset when you get the timer interrupt (thus re-executing the startup code)

    The tradeoff as far as which is lower power depends on your wake-up interval and would need to be tested.

    As far as device selection (your original question), here are two options to consider. Both support LPM3 and LPM3.5 modes as described above, but with different current ratings in each mode.

    Here are the current values, pulled from datasheets:

    1. MSP430FR2000 (www.ti.com/.../msp430fr2000)
    Simple microcontroller from the value line FRAM catalog
    I-avg in LPM3 with 32kHz timer running: 1.0uA typical with a crystal oscillator
    I-avg in LPM3.5 with 32kHz timer running: 0.66uA typical with a crystal oscillator, RAM/register contents lost in between your interrupts (device goes through a reset every 15 minutes)

    2. MSP430FR5858 (www.ti.com/.../msp430fr5858)
    More sophisticated microcontroller from the performance sensing FRAM catalog
    I-avg in LPM3 with 32kHz timer running: 0.6uA typical with a crystal oscillator
    I-avg in LPM3.5 with 32kHz timer running: 0.45uA typical with a crystal oscillator, RAM/register contents lost in between your interrupts (device goes through a reset every 15 minutes)

    If you just need to be in the 1uA range, either device will suit your needs just fine. If you need to get down to the sub 1uA or sub 0.5uA range, than the FR5xx will get you there. Personally, I think the FR2000 will be well suited for your application, but I did want to give you some options to consider.

    Regards,
    Walter
  • Hello,
    I have also found a switch TPS22916 which can support the ON/OFF of the GSM module. Can you tell me any more challenges I would be facing like choice of the clock source, effect of temperature, fail detection, etc.

    Regards,
    Prudhvi Sagar
  • Prudhvi,

    I would recommend that for low power, accurate clocking in this case that you utilize a crystal oscillator with the LFXT feature on the MSP430FR2000.

    This device has fault checking on the crystal, and will switch over to an internal 32kHz oscillator automatically in the event of an external oscillator fault. You can also wake on an oscillator fault. The fail-safe operation is described in Section 3.2.13 of the family user's guide.
    www.ti.com/.../slau445h.pdf

    I think you will find this tech note very interesting:
    www.ti.com/.../slaa792.pdf

    We use ECX-31B SMT crystals on our evaluation modules. Your PPM/deg-C will depend in large part on the crystal specifications.
    www.ecsxtal.com/.../ecx-31b.pdf

    We have the MSP-EXP430FR2311 LaunchPad evaluation module that you can use to prototype and evaluate a solution. This device is very similar to the MSP430FR2000, it just has some additional features.
    www.ti.com/.../msp-exp430fr2311

    Regards,
    Walter
  • Hello,
    This exactly addresses the problem I am looking at. I am new to MSP430 programming. I have SBW in different launchpads but have never made a board and connect it to the ezFET of the launchpad. SBW feels attractive as it requires only 2 pins. Can I get tutorial note on that as well.

    Regards,
    Prudhvi Sagar
  • Hello,
    I have just received a FR2433 launchpad. Planning to implement the whole thing in it and then just transfer to FR2000.

    Regards,
    Prudhvi Sagar
  • Hello sir,
    I have implemented everything on FR2433 launchpad. Now I have confidence to transfer to FR2000. The only step remaining before designing the PCB is selection of XT1. Can I directly use the one on FR2433 and copy the traces as they are?

    Regards,
    Prudhvi Sagar
  • Hi Prudhvi,

    I don't see any issue with you using the same crystal oscillator as the evaluation module. We have a detailed application report available that covers crystal characteristics and PCB layout recommendations if you would like to review it:

    www.ti.com/.../slaa322d.pdf

    You could take the FR2433 LaunchPad layout as-is, but since you know you are going to be using the crystal, I would recommend that you get rid of the zero-ohm shunt resistors in the signal path that are present on that LaunchPad as they are not needed. I also would recommend that you get the crystal and crystal load capacitors as close as possible to the MCU pins.

    Regards,
    Walter
  • Hello sir,
    I have programmed the example of slaa792.pdf. For the first run when the device starts it directly enters into the PORT1 ISR whcih it only has to go once it receives the interrupt. From the second interrupt it works fine. I am unable to uderstand.

    Regards,
    Prudhvi Sagar
  • Hi Prudhvi,

    To clarify, when you run the example, you are seeing that the device enters the PORT1 ISR before you send an edge to P1.3? The code is written such that a low-to-high edge must be seen on P1.3 for the RTC to start counting. From your description, do you mean that the RTC functionality seems to start on its own after power-up (the first time) even if you don't provide an edge on P1.3?

    Walter