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F28335 control card schematic and questions

Alexander A
Intellectual 655 points
Other Parts Discussed in Thread: CONTROLSUITE, TMDSCNCD28335

Hello everyone,

I am digitally controlling a power converter for which I am going to use the control card (TMDSCNCD28335). My requirements for the DSP are most certainly only the JTAG interface, the PWM peripheral, and the ADC peripheral. I am currently designing the PCB of my converter and implement the footprint for the DIMM100 board. Following the schematic in the controlSUITE, I have three questions:

1. What exactly are the 3V3_ISO, RX-ISO and TX-ISO (on the DIMM-100 connector, pin1, pin 2, pin 51 and pin 52) used for? Same applies for the isolated GND. Are any of these necessary or only if a certain peripheral is used?

2. Related to question 1, the digital isolator (component U4A) has SCI-TX and SCI-RX. What are their purpose?

3. To my understanding, all I need to be aware of is to ensure a 5V supply for the control card (which is on the controlCARD itself converted to the necessary voltage levels for the DSP), the JTAG connections TDI, TDO, TRSTn, EMU0, TCK, TMS, EMU1 for programming purposes as well as the pins for my EPWM and ADC peripherals. Is that correct or am I missing anything crucial?

Hope to hear from you. Thank you.

BR,

  • 0
    TI__Guru 57255 points

    Hi Alexander,

    1 & 2)
    This circuitry on the controlCARD is used to generate an RS232 interface which can be used with a computer's serial port.  This was to be utilized via header J3 on the Docking Station baseboard.  This serial interface was designed to be isolated, if desired - to enable isolation both sides of the isolator would need to be powered and some 0ohm or DNP resistors may need to be edited.  The schematics should help you understand this.

    This controlCARD has another option for communicating with a computer - utilizing the virtual serial comport generated by the FTDI chip on the Docking Station. 

    Either the FTDI path or the RS232 path should be used at any one time - or contention is possible.


    3)
    The other thing to be aware of is that the boot-mode pins (for the F28335 these are GPIO84-87).  These pins should be pulled high or low via resistors, as desired, during boot time - and are on the controlCARD.

    You should make sure that any extra usage of these pins on your baseboard is scrutinized.  (you want to make sure that any external circuitry does not impact the ability for the device to boot in the way that you want)

    ===

    NOTE: our kits are designed for evaluation usage and are not intended or tested to be used in end-customers projects - for real systems, we recommend that customers build their own boards.  The expectation is that these kits will be used only in evaluation or prototype systems.

    Hopefully this helps!


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Intellectual 655 points
    Thank you Brett,
    we're using the control card for a prototype for proof of concept purpose. Once we get to the stage of a final product, we will design our own control card then.

    Also thank you very much for your answers to 1)-3). I think I can work from here now.

    All the best,
    Alexander
  • 0 in reply to Alexander A
    Intellectual 655 points

    Hi Brett,

    one more thing maybe regarding the JTAG connections. I am using the XDS100v3 from Olimex.

    And I can see from the schematics of the DIMM-100 that the following signals from the JTAG are nedded:

    TCK (Pin 48)

    TMS (Pin 49)

    EMU1 (Pin 50)

    EMU0 (Pin 100)

    TRSTn (Pin 99)

    TDO (Pin 98)

    TDI (Pin 97)

    4x GND (Pin 47)

    But the 14 pin header from the JTAG has additional signals:

    T_TRTCK

    T_TVD

    T_DIS

    Do you maybe have an idea what they are used for? I am not quite sure if the pins can be left floating or whether they should be put to a certain potential.

    Do you maybe know more about that?

    Thank you very much.

  • 0 in reply to Alexander A
    TI__Guru 57255 points

    Hi Alexander,

    I would recommend that you take a look at the schematics for the Docking Station baseboard as a reference:
    \controlSUITE\development_kits\~ExperimentersKits\ExperimentersKit-HWdevPkg\

    (note that because you will be using your own external xds100v3, all the circuitry including and around U1 is not necessary)


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Intellectual 655 points

    Thank you Brett,

    your hint was indeed very useful and I am almost done with my personal baseboard. One question out of curiousity:

    The LDO U2 creates 3.3V which is connected to pin5 on the JTAG header J2. However, the Dimm-100 does not receive any 3.3V whatsoever. I am now wondering what the 3.3V on J2 could be used for if it wasn't for the DSP itself (as on the controlCARD there is a buck converter that creates 3.3V for the DSP). If the 3.3V pin on J2 does not serve any purpose, I assume U2 will not serve any purpose, either, since U1 and its surroundings will not be present on my personal baseboard.

    Thank you.

  • 0 in reply to Alexander A
    Intellectual 655 points
    Hello everyone,
    I would like to refresh my previous post about the 3.3V on pin5 for the JTAG header J2 since I do not see how that pin is related to the Dimm-100 on the baseboard.

    Can anyone enlighten me?

    Once again, thank you for your time.

    BR,
  • 0 in reply to Alexander A
    TI__Guru 57255 points

    Hi Alexander,

    Pin 5 of the JTAG header is a signal which is provided by the baseboard to the emulator.  It tells some emulators what voltage level it should output its JTAG signals at.

    Some emulators don't really pay attention to this, but some do.

    ===

    We didn't have this 3.3V signal come from the controlCARD because it would 'waste' a DIM100 connector pin.  Furthermore, we wanted to have a 3.3V rail on the Docking Station itself, to make prototyping simpler.

    We also wanted the controlCARD to be powered from 5V only.  We wanted to generate the 3.3V rail for the C2000 chip on the controlCARD itself.  Therefore, we didn't want to waste a connector pin bringing 3.3V from the cCARD to the baseboard just for the JTAG connector. 

    Hopefully this helps.


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Intellectual 655 points
    This helps indeed, Brett. Thank you very much for your answers. I'm having a better understanding now of how and why you designed the hardware as it is.

    Thank you.

    BR,
    Alexander