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LM3150, pin10 "SW" functions

Salah Zayouna1
Prodigy 60 points
Other Parts Discussed in Thread: LM3150, UCC27200

Hi,

I need to get the output of pin 11 "HG" of LM3150 to be referenced to the ground, not shifted by the switch pin. Some other PWM ICs, it is ok to just connect the "SW" pin to the ground to get this done. But for the LM3150 I found from the internal schematics described in the datasheet, the "SW" pin is having another purposes than level shifting the higher side driver, i.e. it is connected to "ERM control", "Zero Current Detect" etc. I made simulation and found that grounding the "SW" will keep maintaining the regulation function (The high side is shifted back to a proper level by an external circuit).

The simulations do not tell all the story. What is expected when "SW" is grounded? any function, or feature is lost? any other thoughts on this?

Thanks

  • 0
    TI__Intellectual 2225 points

    Hi Salah,

    Grounding the SW pin would definitely affect the behavior of the IC, and it is difficult to predict exactly how.  It is likely the simulations do not capture this behavior correctly.

    Can you tell me more about why you need to reference the HG to Ground?  Are you using this for a different topology?

    Perry

     

  • 0 in reply to Perry Tsao96839
    Prodigy 60 points

    I need to use gate driver instead of driving the FETs directly.  By using UCC27200. 

    I agree, simulation does not predict everything. 

  • 0 in reply to Salah Zayouna1
    TI__Genius 16025 points

    Hi Salah,

    This is not possible with the LM3150. I cannot think of any controller that can do this either. Simulations are only behavioral models. They cannot accurately predict specification deviating conditions.

    Thanks,

    Anston

  • 0 in reply to Anston Lobo
    TI__Intellectual 2225 points

    Hi Salah,

    Unfortunately, I don't think this will work with the LM3150.  It sounds like you are trying to use the LM3150 with a higher VIN (hence the need for the UCC27200). Since the LM3150 really needs to have the SW pin connected, this won't be possible.

    Perry

  • 0 in reply to Perry Tsao96839
    Prodigy 60 points

    Sorry guys, it is working perfectly. I got the samples of UCC27200 and build a prototype to generate 1V /1A and 2V/2A . The regulation is perfect.

    Perry, I need it for 24V input voltage, I don't know how you got this idea. For future design, I may seek for higher voltage but LM3150 can not handle more than 42V. But for another reason, I need to use this driver in the current design.

    Still, due to the special needs, I need to do more research on this. My company policy is not allowing me to give more details but as much as related to my question and your answers: It is working and yes we can do this (You can build by yourself and verify if you like)....... If I considered your advice, I should have moved to LT ICs instead of LM3150 for mass production.

    Regards,

  • 0 in reply to Salah Zayouna1
    TI__Genius 16025 points

    Hi Salah,

    I'm glad to hear you were able to make this application work.

    I would like to reiterate that this is not a valid operating application as far as the part is concerned and TI does not provide any assurances or guarantees for modes of operation beyond the datasheet specification.

    Thanks,

    Anston