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MSP430F5659: MSP430 Low power

Part Number: MSP430F5659

Hi Team,

We are using MSP430F5659 in our project where we have power limitation that is 96mW.

At present the controller is taking 3.3V,11mA i e 33mW  with external 4MHz crystal  and software team using upto 20MHz with FLL.

If we use 32KHz external crystal at XT2 instead 4MHz crystal, how much we would power be saved? and is it possible to increase  FLL frequency upto 20MHz from external 32KHz crystal.

Note:  The peripherals used in project are 2XSPI, 1XI2C, 1XUART,RTC  and Internal 12bit ADC, unused pins are configured as GPIO-Output.

Regards,

Srinivas 

Srinivas M

  • Hi Srinivas,

    the XT2 in the MSP430F5xxx family does not support a 32kHz crystal operation. Only high frequency crystals and ceramic resonators.

    I am not sure, whether I understand your use case perfectly. Are you using the 4MHz crystal as reference clock for the FLL/DCO to generate and stabilize the clock at 20MHz?

    Under the assumption it would be XT1, instead of XT2, as this is the only possibility to drive a 32kHz crystal with MSP430F5659, comparing the operation with 4MHz crystal there would be some savings, as 32kHz oscillator operation is below 1µA. XT2 operation with 4MHz crystal is specified in the datasheet with 200µA typical. It is not possible to give max values here, as this is pretty much dependent on the used crystal and the setup. But it gives you the order of magnitude of the savings, means approximately 200µA. The major portion of the current is resulting from the 20MHz clocking of the clock domain/s and modules. So potentially you can limit the consumption by reducing the number of modules and clock domains running at 20MHz. Also check your design against low power consumption rules and recommendations. E.g. if possible, only one clock domain should be running at 20MHz. Consider also lowering the clock by pre-dividers as soon as possible.

    For further recommendations I would need more information.

    Best regards

    Peter

  • Hi Srinivas,

    please let me if there's anything else we can do for you on this topic. Many thanks in advance.

    Best regards

    Peter

  • Dear Peter,

    Thanks for your reply.

    Can 32.768KHz clock  which is used for RTC be used for MCLK and SCLK generation i.e upto 20MHz it can be boosted?

    If yes, kindly let us know the steps to do this.

    Thanks,

    Srinivas M

  • Dear Srinivas,

    yes, a 32kHz crystal can be used in combination with the FLL and DCO to generate a 20MHz clock for SMCLK and MCLK.

    To check, how this can be done, please see for details our MSP430F5xx/F66 User's Guide

    and checkout an example, which comes very close, to your application scenario, and can be found in our TI Resource Explorer within the Code Compose Studio, "msp430f665x_ucs_04.c" . As this code example is using instead of the 32kHz crystal clock the built-in REFO, you need to change the respective settings, selecting the 32kHz crystal as reference for the FLL and the second required change is the target frequency, which in the given example is set to 2.45MHz. Please see the code example comments and the User's Guide for the details on the calculation of the register settings for the FLL.

    Please keep in addition in mind, the Vcore of the MSP430 needs to be adjusted as well, to operate the device at 20MHz. This needs to be done using the SetVCore(PMMCOREV_x); function. Please use the driver lib function for this, as there are certain critical things, to consider, when switching the Vcore voltage levels. Again, please see the User's Guide for the technical details.

    Best regards

    Peter

  • Hi Srinivas,

    I assume your question has been answered sufficiently, thus I am closing this thread.

    Best regards

    Peter

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