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UCD3138: UCD3138 issue with TIDA-00381

Part Number: UCD3138
Other Parts Discussed in Thread: TIDA-00381

Hi Team,

Nice to talk with you!

My customer meet a question about UCD3138. They design LLC with UCD3138 based on reference design: TIDA-00381. Different from initial TIDA-00381 project, they change some conditions:

1. Change frequency range: 150kHz-500kHz

2. Change dead time: 100ns

3. Close all interrupt in addition to CIMINT_ALL_PWM2_COMP

4. Only run voltage close loop

The question is: when Vout jumps from 1.5V to 0.4V(fs=150kHz-500kHz), the full-bridge upper and lower MOSFET tubes in primary side are connected at the same time. 

Could you pls give some comments here? If it makes sense we set 150kHz-500kHz here? 

Many thanks!

  • It makes sense to set 150 to 150 KHz here, but you need to adjust lots of things to make it work.  Most likely the issue is related to going between modes on the LLC, like from PWM to resonant or the other way.

    You may want to try clamping the filter output to different values to see what happens in different modes and to make sure that the transition is working well.  

  • Hi Bower,

    Thanks for your support!

    1. May I know what things we should adjust to make it work in 150-500kHz? 

    2. You mean when Vout jumps from 1.5V to 0.4V, it may works in different modes, right? So if we set up a enough dead time, why it still can be connected at the same time? how it happens? You can see the waveform below: (1CH:DPWM0A; 2CH:DPWM0B; 3CH:DPWM2A; 4CH:Vout)

    Many thanks!

  • I need more information about what is happening here.  Are you suddenly changing the EADC DAC value to go from 1.5 to 0,4 volts?  How much current is flowing at this point?  And what are the specific signal names for the digital scope traces?  

  • Hi Bower,

    Here is no LLC main power circuit connected, just test in TIDA-00381 EVM board, the voltage jump is generated by signal generator, to simulate the output voltage jump as in actual circuit. The purpose is to verify the 150-500kHz frequency range make sense when we change the output voltage quickly.

    For scope trace, 1CH is DPWM0A; 2CH is DPWM0B;  4CH is Vout. You can see when Vout jumps from 1.5V to 0.4V, in X1-X2 time range, 2CH green trace keeps high level so upper and lower MOS is connected at the same time. And it seems this situation happens when PWM mode transfer to resonant mode, so do you have some comments here why dead time changes when control mode changes?

    Many thanks!

  • There's a complicated relationship between the dead times for the two modes. Since you're a TIer I can send you an old preliminary document on the LLC code that could help some.  

  • I've sent you the LLC document and the customer is studying it.  I'm going to consider this resolved.  If there are more questions, please start another thread.