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MSP430F6749A: RTC lost count at high temp

Eddie Koh
Genius 10505 points
Part Number: MSP430F6749A
Other Parts Discussed in Thread: MSP430F6736A, TIDM-AUX-MODULE

Customer running temperature tests on MSP430F6749A. It was observed that RTC becomes inaccurate when tested at 60 degC. Instead of having drifts, customer found out that RTC would, at undetermined intervals, miss 5 counts (5 x seconds counters). Attached is the scope captures on 2 separate instances.

Other points:

1. MSP430F6749A RTC works well at 50 degC and below.

2. Using the exact same Crystal, and load caps, on MSP430F6736A, there is no such issue. (They had been shipping in ~500KU volumes with this same crystal on MSP430F6736A for ~2 years)

3. Customer can accept drifts due to temperature. But this problem is not a drift, but a consistent behavior of skipping 5 counts.

Question:

What could cause MSP430F6749A to have such type of failure, and how to fix it?

  • 0
    TI__Mastermind 49692 points
    Hello Eddie,

    Thanks for your detailed post and screenshots. Since the external 32kHz crystal is the same and the RTC functionality is working on the MSP430F6736A, I would expect that the MSP430F6749A should work fine. Thus, I would encourage the customer to start comparing differences between their two designs to figure out what's causing the issue. These differences would include RTC and AUXVCCx configurations in software and connections in hardware, different external components (besides the crystal) such as power parts and passives (like temperature ratings), and layout differences.

    To isolate the issue more quickly, the customer could purchase our target development board, populate it with the MSP430F6749A and external crystal and load capacitors, and test it at 60C. This would tell them whether it's caused by a software configuration or caused by another external device on their PCB.

    I did find that the AUXPMM2 errata exists in both the MSP430F6736A and the MSP430F6749A, but perhaps AUXVCC2 was not used on the F6736A and was used on the F6749A.

    As a reference, I'd recommend that they look at the TIDM-AUX-MODULE TI Design for our recommendations regarding the AUX and RTC configurations.

    Regards,

    James

    MSP Customer Applications
  • 0
    TI__Mastermind 49692 points

    As a follow-up question, I'm assuming that the signal in the screenshot is RTCCLK, but it may be something different. Can you please confirm?

    Regards,

    James

    MSP Customer Applications

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