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TMS320F28374S: ePWM1 Sync Input sources

Ruta Bhave
Intellectual 440 points

Part Number: TMS320F28374S

I am configuring the ePWM modules on the TMS320F2837xS series of controllers with the following aim-

ePWM 1, 2 and 3 must be synchronized together. (Using ePWM1 as the source)

ePWM 5, 6, 7, 8 and 9 must be synchronized together. (Using ePWM4 as the source, and its SYNCOUT pulse being transmitted to ePWM7)

Referring to TRM (Lit. SPRUHX5F Revision January 2019) - Figure 14-7 Time Base Counter Synchronization Scheme.

1. Is the only sync input source for ePWM1 available through EXTSYNCIN1 and EXTSYNCIN2? Does this have to be provided using a GPIO XABR? What other sources can be used?

2. The sync out pulse mode is selected by selecting a value in the SYNCOSEL registers. Is there another register used to actually trigger the sync event? Is there any way to scope the generated pulse (example by additionally routing it out to an output XBAR maybe?) and/or observe the status of the pulse in the registers using the CCS debugger?

3. In the former synchronization scheme described, can channels 5 through 9 be synchronized using ePWM4 as the source for ePWM5 and ePWM6, and ePWM4's SYNCOUT signal being used as the SYNCIN pulse for ePWM7? I used this setup and noticed a lag/deadband on ePWM7 rising edges at the same frequency. Is it possible to achieve perfect synchronization on 5 ePWM modules this way?

Thanks.

  • 0
    TI__Guru 52080 points

    1. You can use software, or you can take any signal out to a GPIO, then use INPUT XBAR to bring it back into the device and use it as the SYNC input.

    2. You can take out the SYNCOUT pulse using EXTSYNCOUT and using a GPIO to view it on your scope. You can use the SW SYNC FORCE to see the signal pulse.

    3. You can look at the synchronization chain and connect the ePWM modules you want to synchronize. The only thing that would violate the setup is having the SYNC signal propagate through more than 4 ePWMs (1 master and 3 slaves). You can use that same master for other slaves as well. 

    Nima Eskandari

  • 0 in reply to Nima Eskandari
    Intellectual 440 points

    Thanks for your reply Nima

    Nima Eskandari said:

    3. You can look at the synchronization chain and connect the ePWM modules you want to synchronize. The only thing that would violate the setup is having the SYNC signal propagate through more than 4 ePWMs (1 master and 3 slaves). You can use that same master for other slaves as well. 

    -Could you please clarify this a little bit with an example? E.g did you mean that ePWM4 can be used as a source for ePWM 8 and 9?

  • 0 in reply to Ruta Bhave
    TI__Guru 52080 points

    For EPWM4 to be the source for EPMW8 and EPWM9, It also has to be the source for EPWM7.

  • 0 in reply to Nima Eskandari
    Intellectual 440 points

    Hi , I still have a follow up-question on the synchronization scheme. I was able to set up the scheme according to my application's topology and requirements. I can probe the syncout pulse on the EXTSYNCO pin and verify that the synch source module is indeed sending the synch pulse every time the TBCTR value reaches zero.

    My question is what is the expected behavior if the frequency on the synch source module is changed? I have set up the synched PWMs to perform the shadow-to-active period load whenever there is a sync-in signal from the source module. If the frequency on the master module is changed will this also affect the frequency on the slave modules? Does the software have to ensure that the frequency on the master and slave modules is all changed at the same time?

  • 0 in reply to Ruta Bhave
    TI__Guru 52080 points

    The sync signal just restarts the ePWMs at PHS value. This is very much application based. You should in most application change all periods.