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MSP430F5247: Brownout going to low a power state

Jeff Poulsen
Prodigy 30 points
Part Number: MSP430F5247
Other Parts Discussed in Thread: MSP430G2955

Microprocessor used MSP430F5247, migrating from an earlier revision using the MSP430G2955. I am programming in C with CCS 6.1.

The circuit portion below shows the power management circuit involved.

The device is woken by RF energy from a device trying to communicate with it, the ENERGISE signal on the gate of Q3B. The microprocessor latches the power early in the start-up sequence, driving VACT_LA high. The new processor takes longer to stabilise the DCO than the old one, and the energise signal would sometimes collapse before the microprocessor would successfully latch the power on. The issue was solved by putting the latch ahead of starting the DCO with the FLL.

However when the energise circuit collapsed too soon for the latch to hold the microprocessor would sometimes enter a limbo state. Connecting to it with debug in CCS, as a running target, I was able to check the registers and found that the CPU and oscillator were off. The watchdog was functioning but with the maximum interval. I fixed the watchdog issue first, so that the micro would reset soon after getting into this state. Then went on to sort out the real problem of getting the latch happening sooner. Problem solved, almost.

This brings me to my question. How did the microprocessor get into this state?

I have tested the BOR simulating battery failure as part of acceptance testing and found no issues. I can only imagine the microprocessor has a brown-out of sorts when the latching of the power falters. However a complete brown-out should drop the latch and the microprocessor would have to wait for the next transmitted packet to attempt to power up.

Jeff

  • 0
    TI__Genius 15370 points
    Hi Jeff,

    If I understand the above circuit correctly, the RF energy device causes Vcc to be applied to the MSP430. Then the MSP430 must wakeup, go through initialization, and set VACT_LA high which keeps the power on? I can see that this is an attempt to save power but it seems rather complex having the MSP430 control its own power source.

    Additionally, the act of waking up every message might negate any power savings when you could instead use LPM4.5 while waiting for a message, then wake-up based on the ENERGISE signal. LPM4.5 consumes only 0.18uA, whereas at startup the current draw is unspecified. I highly recommend re-configuring to a more stable setup like what I've just described. This would reduce your overall system complexity, component count, cost, and most likely your current consumption as well.

    Best regards,
    Caleb Overbay
  • 0 in reply to Caleb Overbay
    Prodigy 30 points

    Hi Caleb

    Thanks for the thoughts.

    Yes you've described what the circuitry does well. The device spends most of its life powered up after installation. When powered up it spends more than 95% of the time in LMP3 waiting for RF. However the time between manufacture and installation can stretch to two years. Which is why it also has a powered down state to conserve its batteries. The device is potted and can only be activated with RF energy. This cannot be changed. There is a lot more to the power management circuitry that I did not show as it would confuse the issue I'm raising. I would like to simplify a lot of it as it's not necessary, but I'm just the software guy, I get one vote. I would prefer the energise signal to be the input of a Schmitt trigger firing a one-shot of known duration that cleanly powers the MSP430 on and off.

    The changes I have made to the code, I think, have solved the problem by fixing the timing. However I would like to understand the limbo state, as I call it, that the MSP430 got into when the energise and latch timing were not optimal. I have read through the erratasheet several times and cannot find anything that matches. I suspect there may be something in the datasheets that I may have missed or misunderstood.

    Any help understanding this would be greatly appreciated.

    Cheers, Jeff.

  • 0 in reply to Jeff Poulsen
    TI__Genius 15370 points
    Hi Jeff,

    To fully understand what could be happening to the MSP430 I would need more information on what VCC looks like during power up. Is it possible to probe this line during a failure and post the scope shots to the forum?

    Best regards,
    Caleb Overbay
  • 0 in reply to Caleb Overbay
    Prodigy 30 points

    Hi Caleb,

    I'm out of the office for a week. I'll have another go at getting that moment on the scope then.

    Thanks, Jeff.

  • 0 in reply to Jeff Poulsen
    TI__Genius 15370 points
    Hi Jeff,

    Do you have any updates on this?

    Best regards,
    Caleb Overbay

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