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MSP430F6779A: Brownout Reset (BOR) with DVCC slow rising time and falling time may cause MCU get stuck

TinK
Intellectual 765 points
Part Number: MSP430F6779A
Other Parts Discussed in Thread: MSP430F6779

Hi,

About the problem that i have been checking about the MCU get stuck (device does not start).
The MCU get stuck (the device not start) in the actual use field. But it cannot be reproduced in a laboratory.
This cannot use the debugger to debug where the code is stuck. (because the debugger reset the program counter)

Symptoms of the bug were just checked with the H/W pin
(device does not start).

DVCC: 3.419V, AUXVCC1: 3.328V
Vcore pin = 1.42 V (core level 0 AM)
Reset pin = 3.3 V

Now, i suspected cause from slow rising time and falling time as seen from old discuss in forum below.
https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/722493/msp430f6726-cause-and-remedy-to-make-the-mcu-immovable-state/2672286?tisearch=e2e-sitesearch&keymatch=delay%25252525252525252520BOR#2672286

[Power off → Rise speed at power on at around 1-2 V]
Power system A(MCU immovable state after Reset) : 2.13V/s(typ)
Power system B(MCU Normal state after Reset) : 2.68V/s(typ)

[Power off → Fall speed at power on at around 1-2 V]
Power system A(MCU immovable state after Reset) : 0.52V/s(typ)
Power system B(MCU Normal state after Reset) : 0.49V/s(typ)


So I have some questions below.


What is the rise time and fall time rate of the DVCC with the BOR circuit operating correctly (3 V/s)?

What happens when DVCC rise time and fall time are slower than 3 V/s (MCU stuck)?

Does the VDSYS have to consider the rise time and fall time rates for the BOR circuit to function properly?

  • 0
    TI__Mastermind 35720 points

    1. At least 3V/s

    2. It may not cause the BOR event and hold in the reset statey.

    3. VDSYS means the minimum supply voltage. It has no relationship with the rise and fall time.

     

    1, This problem described on previous e2e only happens when the deive is  on power off and power on condictions, and didn't reset compeletely (Very closed to the BOR thd). Is it same on your product? 

    2. There is other posiblity that will cause the CPU halt (For example SD ADC input over the range. My customer meet this problem on i2041). So the key problem is to recreate the issue

    3. If you can't recreate, can you give more information that when it is in actual use field?

    • How many devices meet this problem 
    • When do they meet this problem
    • Is there any pattern of the problem
    • Is this a new project
  • 0 in reply to Eason Zhou
    Intellectual 765 points

    Hi,

    1, This problem described on previous e2e only happens when the deive is  on power off and power on conditions, and didn't reset completely (Very closed to the BOR thd). Is it same on your product? 

    No, it's just an assumption (MCU stuck). We have not had this problem repeat in our lab yet. (In the process of trying to cause the voltage to drop to close the BOR slowly).  Our circuit has no external reset circuit IC as the previous e2e.

    3. If you can't recreate, can you give more information that when it is in actual use field?

    How many devices meet this problem 
    Answer: About 0.5 to 1 % of 1000 devices.


    When do they meet this problem
    Answer: After one month of installation


    Is there any pattern of the problem
    Answer: Yes, only broadly applicable to installations where the AC power system is unstable. (uses an AC to DC power supply circuit)

    Is this a new project?
    Answer: It's a new project that uses the similar MCU (MSP430F6779 ) as the old project. But the features and circuit boards are different.

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