• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 78 subscribers
  • Views 537 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

MSP430F5659: Vcore Capacitor

Jerry Bucci
Expert 1530 points
Part Number: MSP430F5659
Other Parts Discussed in Thread: INA126

Hi,

I have a design that has an intermittent problem. It's a hand held battery operated instrument. Occasionally, maybe 1 in 10-20 times when an external connection is made to the board, the program glitches and causes problems. The connection can for example just be a USB connection with the other end of the USB unconnected(just the wire) or a thermocouple temperature probe that is only interfaced through a bridge to the inputs of an instrumentation amplifier(INA126)There is some sort of noise being introduced and causing a problem.

I thought I solved it when I realized I used a .01uF cap for the Vcore capacitor. I changed it to a 1uF value(~2x the 470nF recommended). That didn't solve it though.

the micro uses a 32Khz for X1 and a 16Mhz for X2. Vcc is 3.1V

Two questions;

1- How critical is the value of CVcore to be 470nF, 

2- What else can be causing this? It doesn't happen when the JTAG debugger is connected , so I cant easily debug it.

Thanks for any ideas.

Jerry

  • 0
    TI__Expert 7365 points

    Hi Jerry,

    1. As documented in the section 5.3 of the device datasheet (https://www.ti.com/lit/ds/symlink/msp430f5659.pdf), the suggested nominal value for CVcore is 470nF. The footnote shows 20% tolerance. I am not sure we have a spec on the suggested min/max values for this.

    2. If this problem does not occur when the JTAG debugger is connected, Is there a possibility that any of the pins from the JTAG interface on your board are not properly pulled up/down? Highly unlikely but thought I would just suggest. What exactly happens when you say 

    Jerry Bucci said:
    the program glitches and causes problems
    ? Are you forced to do a hard reset? Is an interrupt getting generated which is not getting handled by the program?

    Srinivas

  • 0 in reply to Srinivas Lingam
    Expert 1530 points

    Srinivas,

    Thank You for the reply. I was looking for information as to why TI chose 470nF? It's a filter on the core voltage. Why not put a 10uF cap for super filtering. Is it the ESR of concern? Usually, for filtering you may put a large capacitance in parallel with a very small capacitance for higher frequency filtering. 

    As far as what is happening I really don't know. The micro controls a color graphics 480x272 display that has it's own graphics controller(SSD1963) and memory.  When an external signal such as the USB wire being connected to the ground or any other signal being touched by an external connection an "antenna if you will" it causes some sort of noise that messes things up. The display has a PLL that is set to 120 Mhz and I see it goes out of lock when this happens. i need to  do more investigation to troubleshoot it. The problem is it happens very rare but enough to not allow the product to go to production so I have to find it. When the JTAG debugger is connected the grounding is changed and it doesn't occur. 

    Thanks Again. 

  • 0 in reply to Jerry Bucci
    TI__Expert 7365 points

    Hello Jerry,

    Usually, the typical CVcore value is used to obtain lot of the timing related datasheet parameters. 

    Jerry Bucci said:
    The display has a PLL that is set to 120 Mhz and I see it goes out of lock when this happens.

    Jerry Bucci said:
    When the JTAG debugger is connected the grounding is changed and it doesn't occur. 

    Is it possible that there is a ground plane design issue on the board?  

    Srinivas

  • 0 in reply to Srinivas Lingam
    Expert 1530 points

    Shrinivas,

    Yes, it is definitely a noise problem. Due to cost reasons the design was limited to a 2 sided board. I do have some very heavy traces for power and ground around the board. I've been doing this a long time. But i can't change the board at this point anyhow. Good news is that I think I solved the problem by raising the core voltage level from 1.4V to 1.8V and it seems to have solved the issue.

    Thanks,

    Jerry

**Attention** This is a public forum