• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 79 subscribers
  • Views 657 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.

Question about Pin Connections

Lukas
Prodigy 240 points

Other Parts Discussed in Thread: MSP430F6638

Dear All,

I have some questions for my Hardwaredesign with an MSP430F6638:

 

1) Does VBAK pin need a capacitor (Backup function is not used)?

2) Does VCore pin need the 470nF capacitor (Vcore is used :-) )?

3) Do I need a capacitor on VBAT pin (which I connect to DVCC as I have only one battery)?

4) How to connect COM0 if not used?

5) Do I need a capacitor on the RST pin, if  I use internal pull up?

6) Do I need a capacitor on the RST pin, if I use an external pull up?

 

Regards

Lukas

 

 

  • 0
    Guru 227245 points

    Since nobody else answered:

    1) Don't know.

    2) definitely. Without, the MSP won't work. There should be at least 4,7µF on DVcc too. Ose a ceramic one for Vcore.

    3) don't know too. Never dealt with the MSPs with backup funcitonality.

    4) COM0 is an output. So if the LCD is disabled, it should be a static output. Just leave it open. Connecting unused pins to GND or programming them to low outputs is only necessary for port pins, because a floating port input pin will draw excess currents in the input driver if the input voltage comes near the switching voltage (by crosstalk or HF)

    5) on some MSPs, the input pullup is disabled by default. In this case, it is worthless, as you cannot enable it until RST is done, and you need it while RST is going on. Also, the internal pullup is rather weak. A cokmmon value is 10k/100nF, on devices with SBW interface (if you use it), smaller capacitor and higher pullup is to be preferred.
    If you don't have pullup/capacitor, it often hapopens that the whole thing works as long as the FET is attached or the trget is under FET control, but then fails to start up every now and then when the FET is no longer attached or inactive.

    6) yes. Th epurpose of teh capacitor is to keep the RST pin below VCC while VCC is rising. Else it could be that RST is considered high all the time (it rises with VCC and therefore is high), and the MSP starts to operate as soon as VCC crosses the brownout threshold, but is still too low for operation. The capacitor keeps RST below the low threshold for some time, until VCC is no longer rising and RST can keep up.

  • 0 in reply to Jens-Michael Gross
    Prodigy 240 points

    Dear Jens-Michael,

     

    Thanks for your response and explanations. To 6) : Yes, I know. But in table 3.1 of the Users guide they write "47-kΩ pullup or internal pullup selected with 10-nF (2.2 nF) pulldown". I understand that in this way, that I can use an external resistor without capacity. But I'm not sure if that is true (and you would also add a capacitor). The problem is that I have really less space for additional external components and each capacitor brings additional leak currents which I also have to prevent for my application.

    Does anyone have experience with VBAK, VBAT pins?

     

    Regards

    Lukas

     

     

     

  • 0 in reply to Lukas
    Guru 227245 points

    Lukas said:
    in table 3.1 of the Users guide they write "47-kΩ pullup or internal pullup selected with 10-nF (2.2 nF) pulldown". I understand that in this way, that I can use an external resistor without capacity.


    It depends on where you put the brackets on this logical expression. Is it A|(B&C) or (A|B)&C. Based on the functionality of the capacitor, I'd say teh second, meaning that you can either use an external resistor or the internal pullup, AND the capacitor.

    However, on MSPs where the internal pullup isn't active after a reset, you NEED an external one.

    Since the capacitor takes the same space as a resistor, even the first would not make a difference in space usage anyway: Either you use the pullup and an external capacitor, or use an external resistor.

    But it makes no sense to need an external capacitor when usign the internal resistor, but not with an external one. Reesistor is resistor and when you need a capacitor, you need a capacitor, no matter whether there is an internal or an external resistor :)

    From personal experience I can tell you that you will have much fun without the external capacitor. So better make it as large as possible (which isn't much if you plan to use SBW, but for proper startup without FET, bigger is much better.)

  • 0 in reply to Jens-Michael Gross
    Prodigy 240 points

    Hi Jens-Michael,

     

    Jens-Michael Gross said:

     

    From personal experience I can tell you that you will have much fun without the external capacitor.

    :-), ok you have persuaded me.

     

    Regards

    Lukas

     

     

**Attention** This is a public forum