• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 79 subscribers
  • Views 1731 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

MSP430G2230: BOR, POR question

HS FAE Germany
Mastermind 32280 points
Part Number: MSP430G2230


Hello,
customer assumes an ideal 3.3V power supply with 0s ramp up. He uses an external reset device to monitor the power supply and give a reset to the MSP430G2230 at 3.3V.
- Can he release the reset at once or does he need to consider a delay for stabil oscillator, MCU ramp up, ... ?
- Does the internal reset always need the td(BOR) delay of 2ms? Even if the power supplies ramps up very fast (0s)?
- The d/s (page 19) mentioned a V(B_IT–) typ=1.35V and max=1V. Is this correct or should it be typ=1.35V and min=1V?

Regards, Holger

  • 0
    TI__Intellectual 1370 points
    Hi Holger,

    Is there a specific reason that the customer is using an external reset device to monitor the power supply? Typically the RST pin of an MCU is connected directly to the voltage rail powering its DVCC with a pull up resistor and capacitor to monitor reset events for the MCU internally.

    The customer can release the reset as quickly as desired. The MCU will be held in a reset state until it is released, and the MCU will not run initialization code until after it is released. The MCU will automatically hold itself in reset until its power voltages are the required minimum value for its internal oscillator etc. If the MCU is using any external oscillators, the code should check its stability before switching to it, which would be after the reset is released.

    td(BOR) is an amount of time set internally by the MCU to hold itself in reset after VCC increases above a minimum threshold. Looking at the MSP430x2xx Family User's Guide on page 29, td(BOR) appears to change depending on the slope of VCC with lower slopes causing a longer time of at most 2ms.

    The specification mentioning V(B_IT-) having max = 1V does appear to be an error, and I will look into what its intended value is meant to be.

    Regards,
    Ryan
  • 0 in reply to Ryan Meredith
    TI__Mastermind 32280 points

    Hello Ryan,
    they use an external reset because the power supply may rise slowly. They want to run the CPU at 16MHz which needs the 3.3V. Therefore they there is a risk that the MSP430 start the program below 3.3V (or even below 1.8V). I think that could let to undefined behaviour.
    How fast should the power supply be stable at 3.3V?

    Regards, Holger

  • 0 in reply to HS FAE Germany
    TI__Intellectual 1370 points

    Hi Holger,

    The 16MHz oscillator is good to go as soon as VCC hits 3.3V, so the external reset device can release the MCU as soon as it senses that VCC is stable at 3.3V without delay.

    The MCU defaults to using the 1MHz clock and will have some intrinsic delay based on the execution speed of its program before the oscillator is actually set to 16MHz after it is released from reset. Some customers do separately measure the VCC ramp characteristics of their system and add extra internal delay in the code so that the MCU may start operating below 3.3V with the 1MHz clock but wait for a safe, known period of time until VCC is above 3.3V to set the oscillator to 16MHz for time efficiency purposes. It will be important that the external reset device does make sure that VCC is at or above 3.3V at all times the MCU oscillator is set to 16MHz.

    Regards,

    Ryan

  • 0 in reply to HS FAE Germany
    TI__Intellectual 1370 points

    Hi Holger, 

    Was there any more information that you need for the customer? 

    You are correct that the maximum value of V(B_IT-) is not 1V and that value will be removed in future versions of the datasheet, leaving only the 1.35V as the typical value.

    Thanks,

    Ryan

**Attention** This is a public forum