TMS320F28P650DH: TBPHS phase shift abnormal behavior.

sheldon liu

Prodigy 240 points

Part Number: TMS320F28P650DH

Tool/software:

We are using TMS320F28P650DH.

There is strange behavior when use TBPHS to achieve phase shift function.

we take epwm_ex3_synchronization for reference.

EPWM1 create sync out pulse. EPWM2 sync in source is EPWM1 sync out signal. UP counter mode Period: 2000 (200M system clock)

EPWM2 epwm2A -> 0 set high, compA set low. epwm2B -> compA set high compB set low.

Some condition is normal.

But there are two condition that have abnormal behavior. EPWM2A is always high and EPWM2B is always low.

1. compA value < TBPHS.

2. compA value>TBPHS and TBPHS is < 10% period.

We are debugging HW, it is urgent. Thank you for your help.

2 months ago

0 Allison Nguyen 2 months ago

TI__Genius 14290 points

Hi Sheldon,

When using variable phase shift, there can sometimes be cases where an action qualifier is missed due to the counter jumping over a counter compare value during a sync. This depends on the counter compare values, TBPHS, and timing of the sync. Please refer to this similar E2E thread to see if the situation applies to you as well:

https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/1312604/tms320f28379d-tms320f28379d-phase-shift-pwm-missing-pulse

Best Regards,

Allison

0 sheldon liu 2 months ago in reply to Allison Nguyen

Prodigy 240 points

Hi Allison, My problem is different from the thread. we set the TBPHS as 50% period and COMPA is 30% period. sync out signal is at epwm1 counter = 0.

0 Ryan Ma 2 months ago in reply to sheldon liu

TI__Genius 16366 points

sheldon liu said:
1. compA value < TBPHS.

If compA value is less than TBPHS, you will miss your action qualifier setting on the compA event.

TBCTR gets set to wahtever value is in TBPHS at the time of the sync event. Thus if TBPHS is greater than your COMPA register the event attached to that will be missed on either up or down direction.

sheldon liu said:
2. compA value>TBPHS and TBPHS is < 10% period.

In this scenario, do you have any actions on COMPA up?

Assuming TBPHS is < 10% period and COMPA > TBPHS, and you are counting up after sync, you should not miss this action on the counting up event.

BEst,

Ryan Ma

0 sheldon liu 2 months ago in reply to Ryan Ma

Prodigy 240 points

About condition2, it may be not relative to TBPHS, because EPWM1 also have this behavior. we are debugging it with TI local FAE.

0 sheldon liu 2 months ago in reply to Allison Nguyen

Prodigy 240 points

Is there reference design with the T1/T2 to avoid the issue. In the thread, need to use code to enable or disable the T1/T2. How to monitor the TBCTR in code? (if TBCTR<cmpA<TBPHS, enable, else disable T1/T2.)

0 Ryan Ma 2 months ago in reply to sheldon liu

TI__Genius 16366 points

Hi Sheldon,

Yes you can use this as a way to check where TBCTR is, and also you'll need to make sure you know check the CTRDIR if it's up or down.

Best,

Ryan Ma

0 sheldon liu 2 months ago in reply to Ryan Ma

Prodigy 240 points

Hi Ryan, If use code to judge TBCTR, where is the code run? It is not enough fast only if use DSP HW way.

0 Ryan Ma 2 months ago in reply to sheldon liu

TI__Genius 16366 points

Hi Sheldon,

When the sync happens, can you use the T1/T2 events along with your other action qualifier events? You could generate an interrupt on the sync event to check for where tbctr is.

Best,

Ryan Ma

0 sheldon liu 2 months ago in reply to Ryan Ma

Prodigy 240 points

It may be better to optimize the DSP design for this. I have discussed with local TI FAE for detail. He will check it with TI colleague.

Thank you for your reply.

TI FAE will follow up. I close this issue in E2E.

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TMS320F28P650DH: TBPHS phase shift abnormal behavior.