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MSP430FR5869: Power supply current when power on

Part Number: MSP430FR5869

Hi all,

Now we are designing a sensing system with MSP430FR5869s like this figure.

Every MSPs will run 1 MHz Clock or LPM3.
Then the power supply will provide 370uA x 24 = 8880uA = 8.88mA as maximum when system is running.
When we design a power supply, we must estimate the power on current.
I know power on current is bigger than the active current when running in 1 MHz.
But I can't find it in TI's data sheet.

I must know the maximum current when power up.
Please teach me how to estimate the power on current of a MSP430FR5869.

B.R.

Massa

  • Hi Massa,

    first you need to consider not only the typical current but you're right to consider as a worst case active mode current with 0% cache hit ratio which I think in reality will never happen. So as you can see there exist no max spec for this condition in the datasheet so there is nothing else we can provide. We only specify max values for 75% cache hit ratio which covers typical applications.

    Besides this current you also need to consider the modules you are using typical numbers for this can be found in chapter 5.10. 5.10TypicalCharacteristics,Current Consumption per Module.

    On the top it depends how you 24 applications start-up if all comes up the same way wake-up charges needs to be considered as well here table 5-10 in the datasheet provides your information.

    So to support you better exact configuration of the device would be interesting. Alternatively the best way is to record the dynamic power consumption during boot up and during operation under typical conditions to get an idea of the max current.

  • Hi Massa,

    is there any update on this case? If I will close this thread by end of the week (15th Nov. 2019).

  • Hi Dietmar,

    Thanks for your responce.

    Several years ago, we put many MSP430 to a thin power line, and the system was not turned on.

    I know I must consider two current consumptions. 

    One is hardware; turn on the modules and LDO.

    Another one is MPU; especially rise up the DCO and that provides a clock to CPU.

    I want to determin the currents separately, because the sequence to power up with low level reset line may decrease the maximum power consumptions in the thin power line.

    We need some official determinations about power up current.  If you don't have any data, and we must measure the initial power consumtion in our boards, I'll give up to get data and close this thread.

    Best Regards,

    Massa.

  • Hi Massa,

    correct we had issues with inrush currents during power up in scenarios you described and to cover this we put typical wake-up charges in our datasheet.

    These values are based on characterization means real data and last lines represent the charge required by the power supply until user code starts.
    If the user switch e.g. to 16 MHz directly after power up this must be considered on application level same is certain modules gets activated directly.

    So the table below gives you the data for the power up of the device until customer code starts. However charge currents for onboard capacitors are no considered. So if you PCB is un-powered completely and you need to charge caps this must be considered. Because every customer board is designed differently e.g. using LDO or different caps TI cannot provide these data and therefore it is recommended to record a typical current profile of your application and use this for power supply design.

    So again this wake-up charge below considered internal LDO start-up, charging internal logic (Caps) and starting important peripherals like DCO, memory,...

    I think that's what your looking for right?

  • Hi Dietmar,

    Thanks for your clear responce.

    I will try to minimamize the inrush current with measureing the current and MCU behaviors.

    And I'll close this thread.

    Best Regards,

    Massa.