TMS320F28069: Deadband - Active high complementary PWM, please explain

Niclas Samuelsson

Part Number: TMS320F28069
Other Parts Discussed in Thread: TIDM-02000

I'm looking at the example code for implementing deadband in PWM. Here is setup for Active high complementary PWMs

    //
    // Active high complementary PWMs - Setup the deadband
    //
    EPwm3Regs.DBCTL.bit.OUT_MODE = DB_FULL_ENABLE; // 0x3
    EPwm3Regs.DBCTL.bit.POLSEL = DB_ACTV_HIC;      // 0x2
    EPwm3Regs.DBCTL.bit.IN_MODE = DBA_ALL;         // 0x0
    EPwm3Regs.DBRED = EPWM3_MIN_DB;
    EPwm3Regs.DBFED = EPWM3_MIN_DB;
    EPwm3_DB_Direction = DB_UP;

But I don't understand the logic here. It seems to me that, in figure 3.32, the waveform for AHC is achieved by first letting the upper waveform have a rising edge DB (RED) and then letting the lower waveform have RED. This doesn't seem to be the case when looking at the setup code. Can anyone explain to me how the setup works for AHC?

over 3 years ago

0 Luke Jones over 3 years ago

TI__Mastermind 28250 points

Hello Niclas,

It may appear that both waveforms you're referring to have rising edge delay, but really the lower signal has falling edge delay applied to it, and then the signal is inverted. Selecting AHC for POLSEL inverts the signal on the falling edge delay path but not on the rising edge delay path. Notice the inverting functionality in figure 3-31 above DBCTL[POLSEL].

This video may be useful in understanding all the parts of the dead-band submodule:

https://training.ti.com/c2000-enhanced-pulse-width-modulator-epwm-dead-band-submodule

Thank you,

Luke

0 Niclas Samuelsson over 3 years ago in reply to Luke Jones

Prodigy 90 points

Ok. Thank you. Can I also ask how to implement AHC PWM together with Peak Current Control using the internal analog comparator?

0 Luke Jones over 3 years ago in reply to Niclas Samuelsson

TI__Mastermind 28250 points

Hi Niclas,

Are you asking how to implement AHC into the code example on page 325 of the F2806 user guide? Otherwise could you provide more explanation on the design you're trying to implement?

Thank you,

Luke

0 Niclas Samuelsson over 3 years ago in reply to Luke Jones

Prodigy 90 points

I am going to make a peak current control for a phase shifted full bridge converter, as in TIDU248. Is it possible to combine the AHC with the on-chip comparator to control the duty cycle? Maybe there is a better way of doing it

0 Niclas Samuelsson over 3 years ago in reply to Niclas Samuelsson

Prodigy 90 points

Here is the PWM diagram from TIDU248. 4 PWMs are used, and deadband is needed. And I want to use peak current control with the internal comparator:

0 Niclas Samuelsson over 3 years ago in reply to Niclas Samuelsson

Prodigy 90 points

As I understand it, Q2 and Q3 above will use the internal comparator to switch off when the current reference is reached. But then (after a deadtime) the other PWM needs to get high until the current reaches the reference again. How can I make this happen?

0 Chen Jiang ti over 3 years ago in reply to Niclas Samuelsson

TI__Genius 15935 points

Hi Niclas,

Please take a look at figure 3-4 of TIDM-02000 user guide which contains how we setup deadband.

Regards,

Chen

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TMS320F28069: Deadband - Active high complementary PWM, please explain