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External triggered, single PWM Pulse with almost no delay

David Clus
Prodigy 185 points

Hi community,

I'm looking for a solution using a piccolo device to generate:

1) a single PWM pulse,

2) with fixed maximum on time,

3) adjustable overcurrent threshold to disable the pulse,

4) almost no delay between external trigger and pulse output,

5) configurable trigger input qualification,

6) configurable blanking window of overcurrent tripping,

I'm currently thinking of:

Configuring an epwm unit in downcount mode, reload with 1, sync on external pin with a phase value that equals the maximum pulse width, use the comparator with dac and digital compare module to generate blanking and trip zone events.

The drawback i found until now is, according to posts here, that the SYNC-input has an intrinsic delay of 6-7 cycles, and we will add some more delay by input qualification.


Is there a smarter solution (...not using a CPLD/FPGA), or does anyone have other ideas?

Kind Regards

David

  • 0
    TI__Guru 57255 points

    Hi David,

    Based on my understanding of what you're trying to do, I would recommend taking a look at the cycle-by-cycle trip capabilities of the ePWM module to help you.

    I might configure the ePWM with a fixed period and a set duty cycle (set with the maximum on-time) and configure the PWM in up-count mode.  The comparator module can then trip your PWM on a cycle-by-cycle basis based on an external signal if the trigger is analog (or via trip zone input events if the trigger is digital).  Note that both methods can add some filtering and the analog comparator has the ability to enable slope compensation (which can be useful in peak-current mode control systems). 

    Oneshot (OSHT) trip events can also be set up to completely disable the PWM output in the event of a hard fault.

    The ePWM module also has hooks to enable blanking windows so the PWM won't be erroneously tripped.


    Thank you,
    Brett