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MSP430FR5989: Use of VLO in ACLK for ESI Config

Part Number: MSP430FR5989

Dear Ti team,

I have an application flow meter with ESI that runs well on a FR5989 with 32kHz external crystal (based on FLOW ESI GUI). I wanted to check current consumption if i use internal VLO (so I save space on PCB).

	// ACLK Clock configuration
    //Set external clock frequency to ACLK frequency
	//CS_setExternalClockSource(32768,0);

	CS_initClockSignal(CS_ACLK, CS_VLOCLK_SELECT, CS_CLOCK_DIVIDER_1);  
	//CS_turnOnLFXT(CS_LFXT_DRIVE_3);

I've commented the external crystal code and used VLOCLK as source but when I turn on the device it doesn't start calibration, is it possible that ESI is restricted to 32Khz? Something that I can change in ESI config?

I've tried to use LFMODOSC as ACLK source at it runs well (of course it consumes more), so i suppose ESI has a minimum CLK for its operation.

Best regards

Samuel

  • Hello Samuel,

    Looking at the datasheet and some app notes, it does seem pretty important that the ESI peripheral is run at 32.768kHz.  

    This application report goes into detail on adjustments of the ESIOSC oscillator frequency, but also describes how it leverages ACLK as the accurate reference clock for all other ESI related wait and hold timings.  

    Hopefully, this app note can clear up all your questions.

    Thanks,

    JD

  • Hi Crutchfield,

    Unfortunately it didn't. I still can't achieve system working with just the internal oscilator and i don't know why.

    Best regards

    Samuel

  • Hello Samuel,

    That's correct.  We should feed the ESI peripheral a 32.7kHz clock which is really only possible with a crystal.  LFModOsc seems like it's is going to be approximately 32.5kHz but ModOsc is not a high accuracy source so the frequency is going to be +- 15% which I don't think is accurate enough.  

    Thanks,

    JD