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TMS320F28027: PWM Module Configuration for a brushless motor tool

Wenjian Feng
Prodigy 20 points

Part Number: TMS320F28027

We are developing a  brushless motor tool and want to configure the PWM module. During the normal motor operation, we can configure one software PWM signal at the high side and turn off one PWM signal  at low side. But right now we want to turn on all of three low side PWM signals when any one software PWM signal at the high side is low. For example, the PWM duty cycle is 75%, when the PWM signal in one high side is low during 25% of PWM period, we want to turn on all of three low side PWM signals. I can't find the function in doc  "TMS320x2802x, 2803x Piccolo Enhanced PulseWidth Modulator (ePWM) Module Reference Guide". I am not sure that the TI PWM module can support the function above. If yes, can you provide me a datasheet or example code?

Thanks

  • 0
    TI__Mastermind 42195 points

    Wenjian,

                  what are you using currently to turn off one PWM?

    I've never done this before but I imagine you could connect TZ1/2/3 to each of your high-side PWMs. Then configure TZ1,2,3 in the Trip-Zone module to force your lowside PWMs to logic low.

    When working with the F28027's Trip-Zone module it's best to reference the ePWM section for F28069 because that documentation has been updated more recently.

    Additionally when using the Trip-Zone module be sure that you configure all of the trips(CBC, OSHT, DC Events) because the default action is "High-Z" which will cause unexpected results in your PWM output.

    Regards,
    Cody

  • 0 in reply to Cody Watkins
    Prodigy 20 points

    Cody,

    We can't use TZ1/2/3 because TZ1/2/3 are input signals to the PWM module. we’re using TMS320F28027 in our cordless tools. 

    When we’re switching the MOSFETs with PWM signal (continuous software, that is not 100% duty cycle), we want to turn on all the low side MOSFETs when the PWM signal is low within one PWM period. For example, if we’re running a 75% duty cycle PWM, we want to turn on all low side MOSFETs during the 25% low period of the PWM. Is there a register set that allows us to do that?

    Thanks,

    Wenjian

  • 0 in reply to Wenjian Feng
    TI__Guru** 117220 points
    There are two ways to implement this.
    1. Change AQCSFRC to force EPWMxB output high to turn on low side MOSFETs if dead-band generation is bypassed.
    2. Force a one-shot trip (OST=1) in TZFRC, and set TZB to (01) in TZCTL to force EPWMxB to high state to turn on low side MOSFETs.

    But notice that you can't turn on high side and low side of a phase half bridge in the same time, which will short the half bridge.
  • 0 in reply to Yanming Luo
    TI__Guru** 117220 points
    Could you please tell us why the AQCSFRC and TZFRC setting can't meet your requirement? And would you like to have a figure to show what pwm waveform you want?

    Actually, the all 3 low side will be on automatically when all 3 high side are off if you enable dead-band with Active high/Low complementary mode.