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SMPS 12Vin 200Vout, SwitcherPro vs WEBENCH Designer

Jose Esquivel
Intellectual 430 points
Other Parts Discussed in Thread: TPS40210, SWITCHERPRO, TINA-TI

Hi, I'm trying to build a 12 Vin to 200 Vout @ 50mA SMPS.

At first, I used Switcher Pro, and it said I should use the TPS40210, it was the only option showed:

The schematic is the following, I already builded it, but I can't get it working with the calculated components by Switcher Pro, I had to reduce the Soft start capacitor, and the Inductor, this way I get 200v but not 50mA output.

 

So I tried with webench tool, and it says that TPS40210 isn't suitable for my application: "Design cannot be created with this device. Please press OK and select a different device from the list Or click below to show why parts were not found."
 
If I look for the reason, it says that I'm exceeding the duty cycle limit.

SwitcherPro says the duty cycle with my parameters would be 94.6% max.

I made a simulation in tina-ti, with the values calculated by switcher Pro, and it works.
The diode and mosfet aren't the ones which dictated Switcher Pro, but I have changed it's parameters to match with the indicated components.

 

In my physical circuit, with the values suggested by switcher pro, the first thing I noticed was that the frequency was wrong, with 549k and 100pF I should have a 300khz, but instead I have the half, I measured this just connecting Vin, Gnd and the RC network, I measured the same with everything connected.

Should I multiply my Rc resistor in order to force the 300khz? If I just connected power supply and Rc circuit, what could I have made wrong? :(

Second thing, mi Soft start pin vs my Vout looks this way:

I can see that my controller is resetting itself, in the last picture I used a 10uF SS capacitor, same result with a 2.2uF but different period of time.

And finaly if I measure the voltaje at the sense resistor, not at the sense pin, I see this:

So my SMPS is always resetting itself, but I used the values suggested by the software, I have any load apart of the output capacitor.

Is the Webench tool correct when it says that TPS isn't suitable for my application?

Why I can't even get the frequency working?

I'd appreciate any help that you can bring me.

My best regards

  • 0
    Intellectual 430 points

    Should I have 300 khz in the RC pin? Or is it correct to have 150 Khz and internally this frequency is multiplied?

    Because if I set a 300k ohms resistor I can have a 300 khz frequency at the RC pin, but I'm forcing this because it should work with a 549k ohms resistor.

    Tina shows that I should have around 300khz in Rc pin, but also shows that at the start, while SS is charging it has 180 khz.

    Am I seeing the half of the frequency because my controller hasn't started yet?

    300khz with a 300K omhs resistor.

    Tina 180Khz at start

    Tina steady state with 300Khz

    Thanks

  • 0 in reply to Jose Esquivel
    TI__Genius 16025 points

    Hi Jose,

    First off, I'm sorry to hear about these issues and thank you for providing detailed screen shots and explanations for your design.

    To answer your first question, Webench is always preferred over SwitcherPro simply because Webench pulls from an active database of over a 100,000 parts each characterized and implemented within the platform. This allows you to have unique schematics with varying values which still work.

    The other benefit of webench is parasitics calculations which make the simulations and results more thorough. Tina TI or Switcher Pro are not lying when they say that this circuit will work, but because they inherently make approximations, edge operating conditions are far less accurate because there is no wiggle room for approximations.

    What I mean by this is any operating mode that pushes the IC towards the datasheet limits will be incorrectly simulated by any software save for Webench.

    In your case, the duty cycle has far exceeded 94.8% due to parasitics. Hence the IC keeps resetting itself as it tries and tries to deliver what you are asking it to do.

    Attached is a design that will work for your application:

    8865.E2E - Jose - Flyback design for 12V to 200V.pdf

    Let me know how I can be of further assistance.

    Thanks,

    Anston

  • 0 in reply to Anston Lobo
    Intellectual 430 points

    Thanks Anston.


    Sad to know that I've wasted time and effort, but glad because I won't spend more time trying to make it work as Switcher Pro said.

    I'd like to know if is it definitive? no way to do that? I mean with the Switcher Pro values, I wasn't able to achieve the objetive, but varying some components, I got some results, but I know that what I made is a hack, not the spected usage of the IC.

    I was able to get 200Vout from 12Vin, but with IoutMAX= 10mA not 50mA as I spected.

    I'd like to share some information in case that some one else could need it.

    If you're facing problems with TPS40210:

    If it is restarting over and over again, instead of increasing SS capacitor, remove it or put a 10pf, it will force to start, then you can try from small capacitor to bigger one up to the Vout starts to fall.

    You can also try to increase the gate resistor, the higher resistance the higher current through the Mosfet, so more chances to reach the desired voltage, but more power dissipated by it. I set a 47R.

    Also reducing the inductor value, allows a higher current.

    That's what I did.

  • 0 in reply to Jose Esquivel
    TI__Genius 16025 points
    Hi Jose,

    Practically duty cycle would exceed the limits of the IC. You can play with the values and maybe achieve a few mA's of current but that's really it.
    I like to fiddle with these circuits to learn as much as possible before I start the next project. Helps provide a design perspective on what's really going on.

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    Intellectual 430 points
    Thanks a lot. My best regards
  • 0 in reply to Anston Lobo
    Intellectual 430 points
    One more question, where in the datasheet specifies the maximum duty cycle?
  • 0 in reply to Jose Esquivel
    Intellectual 430 points
    Figure 2 gives some idea of the duty cycle limitations when using the TPS40210. The max duty cycle is determined by the minimum off time of 200ns. With 94% duty cycle the off time is about 1.2µs. The 200ns off time gives a theoretical max duty cycle of 99% with 50kHz switching frequency.

    e2e.ti.com/.../226835
  • 0 in reply to Jose Esquivel
    TI__Guru**** 191445 points

    I should also add that while switcherpro can sometimes be a useful tool, development ceased several years ago and any errors or bugs have not been addressed.  You have to use it at your own discretion.  I still use it occasionally, but I know it really well and can spot issues with it when they occur and work around them.  It does have quite a few features that are lacking in webench.