UCC2897A: Support Needed: No Drive Signal on Pins 15 & 16 in PSpice Simulation

Hi,

Your simulation circuit is blur so I cannot check. Please provide a readable circuit so I can check.

Hi,

Did you say pin 15 and 16 do not show drive signal? I suppose you mean pin 14 and 15. Please clarify.

What waveforms from VIN, VDD, VREF, FB,SS, LINEUV, LINEOV, CS and RSLOPE?

Hi,

VIN is from external - if you do not see this then your circuit is not set up correctly or your simulation package is with problem. You need to contact your software provider to help.

Hi,

Please provide VIN, VDD and VREF waveforms at power on.  

You need to get these correct first before you can move to the next steps.

Hi,

Not sure where you got wrong.

I need to see your simulation of VIN, VDD and VREF waveforms at power on in order to find what to do next.  

Hi,

Where is C136?

Why Vin is so low? R37 and R53 to make LineUV to reach 1.27V. With your Vin and R37 =6.8M and R53 =133k it does not seem LineUV can reach > 1.27V then no pulses can present. So you need to recalculate R37, R53 and increase Vin to make LineUV >1.27V then show me the waveforms of VDD VREF VIN AND LINEUV TO go from there.

Hi,

Please provide waveforms of VREF FB SS and CS

Hi,

I see SYNC is shorted to GND. If so you need to open this pin to see if you can get the pulses.

Hi ,

Based on the datasheet the SYNC pin should be open if not used.

So this needs to resolve.

Hi,

OUT and AUX are overlapped. Can you separate the waveforms so not overlap them to help check individually to find how OUT waveform is.

Hi,

I think we can change the debugging approach.

I did a very similar circuit on TINA TI with the same UCC2897A PSpice model you used in your simulation. My circuit works fine like the below.

My circuit is attached. I think you first make a circuit same as mine in your simulation. Then conduct the simulation to make sure it works like mine. Then gradually change to your need. One or two components at a time. Then simulate again. If you can get through then the debugging is done. If any stuck then we can study why change that component stopping working.

Hi,

So you have both OUT and AUX with pulses. This means the IC works.

Now you need to change the circuit to your need. But change a few components at a time to see if still ok to get the pulses. 

As the circuit is very similar to your original so you change the components to what you designed then to see if the pulses are still ok to generate.

I think the IC works on your simulation so in nature you should get your circuit work. Previously not showing pulses should relate to something not setup correctly.

Hi,

I do not know which MOSFET can work in your simulation software. I think one way is to try different MOSFET from your software library until you find one can work. Then you can change the MOSFET property to the same as the MOSFET you want to use.

Another way is to get your software vendor support to help find why.

I do not have your software so not able to know why your MOSFET cannot work. So you can try the above to resolve.

Hi,

How did you connect the MOSFETS?

Hi,

What is the MOSFET type connect to OUT pin? It looks a P channel MOSFET - if so then it is not correct. The MOSFET connect to OUTpin  should be an N channel MOSFET.

Hi,

Another thing, how UCC2897A VDD and PVDD are biased? It does not seem you circuit has bias to these two pins.

I added the MOSFETs to the circuit previously sent to you and the circuit running ok.

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