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TMS320F28335: Help understanding ePWM and role of RN3 resistor on F28335

mike buba
Intellectual 470 points
Part Number: TMS320F28335
Other Parts Discussed in Thread: TMDSDOCK28379D

There are 6 ePWM channels in F28335 Control Card. All 6 are high-resolution PWMs (HRPWM). Each channel has A and B, where B is shifted by 180°. On a F28335 those GPIOs are:

ePWM1A -- GPIO-00
ePWM1B -- GPIO-01
...
ePWM6A -- GPIO-10
ePWM6B -- GPIO-11

What is the role of RN3 resistors (from Schematic [R2.2])? ePWM1 - 4 are connected through 33R and ePWM5 and 6 are not.

In my application, I have 2 step-up converter (20kHz switching frequency) and PWM inverter (4kHz switching frequency). In this arrangement, step-up converter PWMs are connected to ePWM1A and ePWM2A and inverter legs to ePWM3A/B, ePWM4A/B and ePWM5A/B. Meaning, one leg is connected to GPIOs without resistors. Are there any limitations of connecting this in terms of speed or something else? I can connect step-up to ePWM5 and ePWM6 (i.e. without resistors), but will this affect the operation as those signals are the order of magnitude faster than inverter's?

I am planning to incorporate docking station on the PCB board so would like to know in advance if I will encounter some issues.

Similarly, on ADC pins there is no noise-filtering capacitors and ESD protection installed on ADC-A6/A7/B6/B7. Luckily, I am not using all ADC so could rearrange them. For PWMs I am using 5 ePWM blocks.

  • 0
    TI__Mastermind 42195 points

    Mike,

    I suspect those resistors were added to reduce EMI and slow down the edge rate on those PWMs. 

    The ADCs received this circuitry to protect them, it should be applied on all ADC channels. In our newer designs we decided to include it on all channels.

    Please note that this is an EVM and is not intended to be used in any end applicaiton. It is fully on the user to design, develop, and validate a system which fits their needs.



    Regards,
    Cody

  • 0 in reply to Cody Watkins
    Intellectual 470 points

    Thanks Cody.

    No worries. I am not planning anything commercial, it is an academics research project. I am experiencing USB communication issues between docking station and PC when increasing the inverter voltage and power. I was told in one of the previous queries this might be related to ground float, so putting all on one board (control and signal conditioning) seems like a reasonable way to go.

    Re. resistors: so the way forward is to use GPIOs with resistors for inverter and without for fast switching step-up converter. Adding 33R resistors to other 8 channels on the J4 and J5 connectors on the docking station should have the same effect as RN3 on the first 8 channels?

    Kind regards

  • 0 in reply to mike buba
    TI__Mastermind 42195 points

    Mike,

    yes it will act very similar.

    Please also note that there are newer C2000 devices with more features available! If you're starting a new project I might suggest looking into the F2837x family with TMDSDOCK28379D. This evaluation module also uses a newer "HSEC" connector which is readily available for purchase. The F28335 controlCARD uses a DIMM100 connector which is now hard to find. If you ever build your own baseboard it would be good to be in the newer HSEC form factor.

    Take a look at some of our other core c2000 devices offered here they all have evaluation modules:  

    Nonetheless, F28335 is a fantastic device, and if you already have something reusable developed on it I would probably stick with it.

    Regards,
    Cody