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TMS320F28027: Peak Current Mode using the Comparator and Tripzone. Workaround for Deadtime?

Daniel Both
Prodigy 20 points
Part Number: TMS320F28027

Hello,

I'm implementing Peak Current Mode (PCM) Control for a buck converter. The diode has been replaced with a second MOSFET for reduced switching losses (synchronous converter). Therefore, a dead-time between epwmxA and -B is required.

However, when using the comparator for PCM, the ePWM is controlled via Trip-Zone module (as shown in SPRUGE9E and SPRABU2). Since the Trip-Zone module is located behind the Dead-Band generator, I figured a classic implementation for a dead-time between epwmxA and -B  is not possible. 

Is this conclusion true, and if so, is there a workaround for implementing a dead-time when using the comparator for PCM?

Thanks in advance!

Best regards,

Daniel

  • 0
    TI__Genius 10820 points

    Hi Daniel,

    Your conclusion is partially correct. You can make PCMC control of a synchronous buck/boost converter work on F2802x device with additional time-critical software. This software is needed for some PWM register re-configuration and/or time critical actions. This software overhead will limit the highest switching frequency you may achieve and additionally have a detrimental effect on the CPU MIPS usage.

    We have an example of this for a phase shifted full-bridge power stage using F2802x device here 

    http://www.ti.com/tool/TIDM-PSFB-DCDC

     

    The F2837x, F2807x and F2804x devices have enhanced PWM features that allow dead-band to be inserted for a PCMC application without any software intervention. You may take a look at those devices for a simpler solution.

    Hope this helps.

    Hrishi 

  • 0 in reply to Hrishi Nene
    Prodigy 20 points
    Hi Hrishi,

    Thank you, you already helped a lot.
    However, I'm having a hard time understanding the example project you suggested.

    If I understood correctly, the ISR is still triggered by the ePWM and the ePWM is still tripped by the comparator block. I fail to find the implementation for the dead-band in this context and the additional time-critical software you mentioned.
    Could you exemplify the additional time-critical software? What is the trigger source for this additional software or is it included in the ISR triggered by the ePWM? What are the specific changes to the PWM register done by this additional code, and what do these changes effect?

    Thanks in advance!

    Best regards,

    Daniel
  • 0 in reply to Daniel Both
    TI__Genius 10820 points

    Hi Daniel,

    I prepared this attached solution a few years back. This is for implementing PCMC control of a synchronous buck or boost power stage using F2802x or F2803x devices.

    I hope this helps.

    Hrishi

    6443.PCMC_Sync_buck.pdf