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MSP430FR4133 Support required

Pradhan Rivankar
Expert 1080 points
Other Parts Discussed in Thread: MSP430FR4133, MSP430FR2633

Hello Sir,
We have been using MSP430FR4133 controller for our product and for which we have developed a prototype device and to check the function of the project. In which we are using CAPACITIVE touch which is in built function in MSP430FR series. We are using single touch as a button in project, where we have designed four such button and creating an event. But we are finding some problems during a high spike in 230V AC or noise created AC load creates noise or high harmonics. During these time the CAPACITANCE value is been changed due to which the device starts malfunctioning. I have given a brief description of the prototype design of CAP touch below for the better understanding and reference. So, please do refer and reply at the best to help our product to be a successful one. We are now on the end of the product development, also we are going do 2nd revision for which we need guide lines to improve our product.

Design description:
1. using CAP touch as single touch button.
2. designed as CAP Addon card which is interface with controller through header pin connector of 2.54mm pitch.
3. the MCU MSP430FR is placed near to connector as to avoid the loop structure or antenna creation.
4. Layout of CAP button:: PAD size - 10mm
:: keepout dist. from PAD to GND - 1mm (recommended)
:: GND plan top layer 75% hatched type and bottom layer 25% hatched type
:: the shape of GND plan to PAD is hexagonal type
:: PAD shape is round
:: PAD is unmasked green open to air
:: NP ohm pull down resistor is connected on signal line from PAD to controller, it is near to MCU
:: we have keept 2mm of through hole in center of PAD for LED indication.
:: signal trace is 12mils(0.3mm).
So, describing these design layout please help us to solve our problem and issues regards the same. Also I have described the doubts and query as we are doing REVISION-2 layout for CAP touch card PCB. So, please do refer and reply as soon as possible as it is very much urgent.

Query and Doubts:
1. what should be the distance between PAD and MCU OR placement of PAD from MCU. It is compulsory for us to design CAP touch as separate PCB only as addon card to controller PCB.
2. should we connect resistor in series from PAD and MCU for ESD protection, as to avoid RF noise nearer. IF yes what should be appropriate value of the resistor. Also where should the resistor be placed, whether near to MCU or PAD.
3. Layout guidance, what should be GND pouring hatched type or 100% filled GND.
4. what should be the size of average PAD for a human touch(recommended 10MM)
5. whether the PAD should be mask with green layer or not
6. what should be the PAD shape for smooth sense.

Kindly help to support so that we can take our product in production.

Thanks in advance

Pradhan

  • 0
    TI__Guru**** 202086 points
    Hello Pradhan,

    1. The distance between the PAD and MCU should be as short as possible to minimize Ctrace, which is a form of parasitic capacitance. Higher parasitic/steady-state/baseline capacitances result in lower sensitivity, therefore making your capacitive touch button signal more difficult to recognize. Separating the PAD and MCU between PCBs is not recommended since it introduces several parasitics including longer trace lengths and pin connectors, hence making the cap touch button less effective.

    2. ESD protection for noise immunity is especially important if you are noticing AC load noise on the system that will directly affect the SNR. Series resistors should be placed as closely to the MCU as possible and their value is dependent on factors such as additional ESD protection (TVSs, decoupling capacitors, etc), max IC voltage and current, and so on. More information is supplied by the MSP430 System-Level ESD Considerations Application Report (SLAA530): www.ti.com/.../slaa530.pdf

    3. GND pouring should be hatched, spaced as far away, and placed on the layer furthest from the trace lines to reduce parasitic capacitance. Separation between the electrode and coplanar GND pur should be at least one half the height of the covering materials.

    4. A circular electrode of about 10 mm in diameter, with an electrode larger than the decal, is recommended for maximum human touch sensing.

    5. The PAD should be separated from the surrounding environment with both a soldermask layer and overlay.

    6. Circular electrodes are best for human touch.

    This is all covered in the Capacitive Touch Hardware Design Guide (SLAA576): www.ti.com/.../slaa576a.pdf

    Regards,
    Ryan
  • 0
    TI__Guru 53525 points
    Pradhan,
    The noise situation you have described appears to be related to conducted noise as described in IEC6000-4-6. The pinOsc technology does not provide any mechanisms within the measurement to deal with this type of noise. This is highlighted in this comparison with the MSP430FR2633, www.ti.com/.../slay048.pdf . You really need to suppress this noise at the source.

    Regards,
    Chris
  • 0 in reply to Chris Sterzik
    Expert 1080 points

    Thanks Chris

    You support was very much valuable. Appraciate it.

    Regards

    Pradhan

  • 0 in reply to Pradhan Rivankar
    Expert 1080 points

    Hello Sir,

    Please help us in reviewing the capacitance pcb layout attached below. Whether any changes is to be done or not. You have so helpful to us after which we where confident in the same and reached to the conclusion. So, please do needful for the same and reply as soon as possible.

    Awaiting for your kind response.

    Thanks and regards

    PradhanGerber Release.zip

  • 0 in reply to Pradhan Rivankar
    TI__Guru**** 202086 points
    It doesn't appear that any changes have been made to address the issue as stated by Chris, which is that noise needs to be suppressed at the source. My original review of the board was under the assumption that this was a CapTIvate design, and as this was proven incorrect no changes to the capacitive touch PCB were recommended. Altering this PCB will not affect the noise originally described.

    Regards,
    Ryan

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