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UCD3138: UCD3138 achievable control strategy

Zoe Zhou
Prodigy 100 points
Part Number: UCD3138

Hi :

I have a question about how to implement CRM control with UCD3138.

In fact, I want to know if there is a good way to reset the DPWM counter.

I saw three ways from the specification:

1:DPWM ENABLE

2:Sync  Received

3:Counter reaches PRD

But I think these three methods are not suitable for CRM control of frequency conversion.Is there any way to reset the counter by changing the value of a register(Generally, this method is used in C2000.)?

I saw this sentence in the user manual:in all modes but the resonant modes, the period is a fixed value, in the resonant modes, the period comes from the output of a filter.

Does the red highlight indicate that the UCD3138  is not suitable for CRM control (Pulse Frequency Modulation)?

I am looking  forward to your reply!

Thanks very much and best wishes~

Zoe

  • 0
    TI__Genius 17090 points

    Zoe, we do actually use the sync pin, triggered by an external event, to stop the DPWM period and restart it from the beginning.  If you can give more detail on your specific application, I will see what we might have to get you further along.  Obviously we use an external hardware signal to trigger the sync.  Although I think we've used a different DPWM pin connected to the sync pin, And the edge on that pin was triggered by one of the internal comparators monitoring a voltage.  We were trying to stop the DPWM somewhere around zero current, I think,  So even though the signal was external, the hardware was all UCD.  

  • 0 in reply to Ian Bower
    Prodigy 100 points

    Hi Ian：

    Thanks for your quick reply!

    I want to do a CRM boost. The turn-on time is determined by filter. The turn-off time is determined by the external current zero crossing.Please help give some advice.

    About the sync signal you said,I have just looked at the specification.Do you mean this register?

    Can I understand this: When there is a transition signal from low level to high level on the sync pin, UCD3138 stop the DPWM period and restart it from the beginning ? So I can connect the external zero current detection signal directly to the sync pin?

    If anything is wrong, please point out.

    I am looking  forward to your reply!

    Thanks very much and best wishes~

    Zoe

  • 0 in reply to Zoe Zhou
    TI__Genius 17090 points

    That register you can just leave in its default state.  The SYNC pin default is an input, and you want to leave it that way.  the key bit is the EXT_SYNC_EN bit in DPWMCTRL1 in the DPWM registers.  If you set that bit for a specific DPWM, that DPWM will have its counter rest and restarted by a rising edge on the SYNC pin.  

    When you say the on-time should be determined by the filter, you really mean the off time from the start of the filter to the turn on time, right?  The edge which is controlled by the filter is the falling edge of DPWMxA.   and the rising edge of DPWMxB.  So I guess you could use DPWMxB for your signal.  The secret to doing this is to set EVENT4 to 0.  That way DPWMxB will be turned off as soon as the DPWM is reset by the sync signal.  

    I should mention that you need to ignore all the other things that say sync in the DPWMCTRL registers they are for sync between DPWMs, not external sync.  And for SYNC FETs, not external sync.