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MSP432P401R: Pin Connections & External Circuitry to the MSP432P401R [HELP]

Shane Yost
Prodigy 90 points

Part Number: MSP432P401R

I'm spinning a MSP432 board and instead of posting multiple questions I figured I would place them here all in one spot.

1) This is technically my first board I'm spinning by myself and find it confusing which documentation I should reference when determining how to wire up external pins on MSP432P401R. For example, what do I do with unused pins? There is a large database of documentation so I was wondering which docs would be most helpful.

2) I noticed when I was referencing the schematic layout of the MSP-EXP432P401R Launch Pad you guys use 10V/20%/X5R capacitors for the Analog VCC circuity but on the LFX and HFX external circuitry you use 50V/5%/NP0 capacitors. Why the difference in capacitors?

3) This is probably a stupid question but I noticed that there is no DVCC3. This is strange to me because there are three DVSS's (DVSS1, DVSS2, DVSS3) but only two DVCC's (DVCC1, DVCC2). Same thing goes for AVCC3. Did I overlook something?

4) What is VSW used for? How should this pin be connected externally. This question technically goes hand in hand with question 1.

5) Why are you connecting Analog VCC to Digital VCC, isn't that bad? I've read a few forums on here stating this is bad and that there should be some isolation between the two?! What purpose does the 0ohm resistor serve? It's 0 ohms so I'm confused why it's even there? Is there an alternative method in how I can wire this up (documentation/reference design)?

  • 0
    TI__Expert 8510 points

    Answers below:

    1. If you want to make your board more generally useful, I would at least bring out your "unused" IOs to a pin so that you can connect it later if needed. Remember that some ports over port-remapping capability, so you can make functions appear at various IOs if your needs change.

    2. The components are different on the crystal inputs because of a need for greater accuracy on the oscillators which form the time basis for the entire chip.

    3. You're not overlooking anything. Vcc and Gnd pin counts won't always match up.

    4. VSW is used for the switching DC:DC regulator. If you look at the LaunchPad schematic, you'll see an inductor must be connected to this pin on one side and to a set of capacitors on the other for the DC-DC to work properly. This is valuable if you are trying to operate at higher speeds, since the DC-DC is much more efficient than an LDO regulator at higher current levels. (so, saves power)

    5. Ultimately, both Analog and Digital supplies have to be connected to something. Shorting the works in most cases for this evaluation module, but the zero-ohm resistor connecting the two supplies on the LaunchPad is there if you want to separate them for better isolation. Your application may need greater isolation. In which case, you might drive AVCC and DVCC with separate regulators on the board level.  You do still get some benefit just from having the separate supplies and connecting them off-chip.  

    -Bob L.

  • 0 in reply to Bob Landers
    Prodigy 90 points

    Hi Bob ~

    Once I have a schematic layout done may I upload this here for review/feedback? Is that ok or is there a better alternative in receiving a bit of review for the first time?

    I'm supplying power over this FTDI232R chip. Therefore, 3.3V will be supplied to the msp432. Can I just connect both AVCC and DVCC to this 3.3 output pin on the FTDI chip while keeping the rest of the circuitry for AVCC and DVCC in the same configuration as the LaunchPad?

    Lastly, does TI offer any schematic advice on how I should wire up a FTDI chip (reference schematic, etc)?

    Thanks,
    ~S

  • 0 in reply to Shane Yost
    TI__Expert 8510 points

    Shane,

     Generally, I would say we can't do board reviews via E2E. If you have specific issues about the device, how it should be connected, or guidelines for PCB design,  then we can respond.  For board layout questions, the first thing I would do is refer to the MSP432P4 launchpad documenation & Design files.

    PS- For reference, the MSP432E4 (different device, but some general rules still apply) Design guidelines are helpful.

    As for AVCC/DVCC- yes, you can connect both to your 3.3v (the launchpad does this). Note that you will want to ensure that you avoid excessive noise, as you may impact ADC measurements by doing this. Ensuring that the FTDI232 can source enough current is important here.

    As for the FTDI chip- that's manufactured by another company, so you'd have to go to their web site for that information.

    -Bob L.

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