TIDM-1007: Cycle-by-cycle (CBC) protection setting and result

Can you describe the difference between the pictures? The second one is OST turning the signals off, the first one is CBC? or DCEVT?

Dear Nima,

The first figure is by DCAEVT2, but the result was wrong (not as expected)

The second figure is by DCAEVT1, and the result was correct (as expected).

The user wants to do it by DCAEVT2 because PWM can be recovered automatically once the over current events disappear.

Wayne Huang

So the user doesnt need any CBC or OST. They just need DCxEVT to directly manipulate the output and turn it off when the signal is present?

Dear Nima,

Yes, the user's wants to use PWM cycle-by-cycle (CBC) as current limiting in this case.

The current is sensed by the comparator for DCAEVT2.

From the above codes in the first post, you can see they use DCAEVT2 as the source in TZSEL and so that it can be CBC latched following Figure 18-41. Trip-Zone Submodule Mode Control Logic of the TRM (http://www.ti.com/lit/ug/sprui33c/sprui33c.pdf).

But the result was not as expected as the figure 1 in the first post, so we are asking this and wonder if there is anything wrong.

Wayne Huang

Dear Nima,

Do you have any update?

Wayne Huang

I wrote this example to configure the DC module for CBC. Take a look at below:

    //
    // To enable DCAEVT1 as one shot trip sources un-comment below
    // You will need to un-comment the lines in the TZ ISR to re-enable
    // the PWM after a one-shot event has occurred.
    //
    // EPWM_enableTripZoneSignals(EPWM1_BASE, EPWM_TZ_SIGNAL_DCAEVT1);

    //
    // Select TRIPIN1 (INPUT XBAR INPUT1) as the source for DCAH
    //
    EPWM_selectDigitalCompareTripInput(
            EPWM1_BASE, EPWM_DC_TRIP_TRIPIN1, EPWM_DC_TYPE_DCAH);

    //
    // DCAEVT1 is generated when DCAH is low
    //
    EPWM_setTripZoneDigitalCompareEventCondition(
            EPWM1_BASE, EPWM_TZ_DC_OUTPUT_A1, EPWM_TZ_EVENT_DCXH_LOW);

    //
    // DCAEVT1 uses the unfiltered version of DCAEVT1
    //
    EPWM_setDigitalCompareEventSource(
            EPWM1_BASE, EPWM_DC_MODULE_A, EPWM_DC_EVENT_1, EPWM_DC_EVENT_SOURCE_ORIG_SIGNAL);

    //
    // DCAEVT1 is asynchronous
    //
    EPWM_setDigitalCompareEventSyncMode(
            EPWM1_BASE, EPWM_DC_MODULE_A, EPWM_DC_EVENT_1, EPWM_DC_EVENT_INPUT_NOT_SYNCED);

    //
    // Action on DCAEVT1
    // Force the EPWMA LOW
    //
    EPWM_setTripZoneAction(EPWM1_BASE,
                           EPWM_TZ_ACTION_EVENT_DCAEVT1,
                           EPWM_TZ_ACTION_LOW);

That is for one-shot. It needs to be similar to CBC.

//
    // To enable DCAEVT2 as CBC trip sources
    //
    EPWM_enableTripZoneSignals(EPWM1_BASE, EPWM_TZ_SIGNAL_DCAEVT2);


    EPWM_selectCycleByCycleTripZoneClearEvent(EPWM1_BASE , EPWM_TZ_CBC_PULSE_CLR_CNTR_ZERO);

    EPWM_disableTripZoneAdvAction(EPWM1_BASE);

    //
    // Action on DCAEVT2
    // Force the EPWMA do not change
    //
    EPWM_setTripZoneAction(EPWM1_BASE,
                           EPWM_TZ_ACTION_EVENT_DCAEVT2,
                           EPWM_TZ_ACTION_DISABLE);

    //
    // Action on DCAEVT2
    // Force the EPWMA LOW
    //
    EPWM_setTripZoneAction(EPWM1_BASE,
                           EPWM_TZ_ACTION_EVENT_TZA,
                           EPWM_TZ_ACTION_LOW);

What I think may happen is you have the "high impledance action turned on at the DCAEVT2".

If it is possible that your understanding on the DCAEVT and CBC are not correct. 

When to use:

    EPWM_setTripZoneAction(EPWM1_BASE,
                           EPWM_TZ_ACTION_EVENT_DCAEVT2,
                           EPWM_TZ_ACTION_LOW);

That is if you want the EPWM signal to go low as soon as a DCAEVT2 is available and restore to default when the DCAEVT2 signal disappears.

When to use:

    EPWM_setTripZoneAction(EPWM1_BASE,
                           EPWM_TZ_ACTION_EVENT_TZA,
                           EPWM_TZ_ACTION_LOW);

This is if you want the EPWM signal to go low as soon as a DCAEVT2 is available and restore to default only when the CBC CLR PULSE event occurs, maybe at EPWM CTR=ZERO. THIS IS THE CBC mode.

Dear Nima,

You can see the codes I showed on the first post.

The users follows the CBC mode that you showed in the last post, but it seems there is still something wrong that we are still clarifying.

I think we can talk offline for more detail.

Wayne Huang

Will post the solution once ready for other customers to view.

Wayne,

Did you try the sample code?

Nima