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LM25116: Would like to know about the pic connection

Swetha Revanna
Prodigy 50 points
Part Number: LM25116
Other Parts Discussed in Thread: LM5116

Dear Sir/Madam,

I am working on a project to develop regulated power supply for the laboratory application. In my design, I am using the buck controller IC LM25116, which has high HO, Low drive LO and a switch SW pins. But in my design, I am using push pull amplifier circuit to drive the high side of the n-channel MOSFET and for the protection I have used pulse transformer after the push pull circuit and then from the pulse transformer to the gate drive of the MOSFET. So, here I need to use only the HO pin from the controller and I do not know how the other pins are connected. It would be great and thankful to you for the answer in advance.

With kind regards,

Swetha

  • 0
    Prodigy 50 points
    LM25116: Would like to know about the pin connections which are not in use
  • 0 in reply to Swetha Revanna
    TI__Mastermind 30870 points
    Hello,


    Do you still need the Ho out to be level shifted above Vin to Drive an NCH MOSFET? or are you requiring the Ho to be VCC above Gnd?



    Do you have a basic schematic of what you are trying to do as I am having a difficult time following exactly?

    Thanks in advance.

    David.
  • 0 in reply to David Baba
    Prodigy 50 points

    Hello,

    Yes, I do need HO pin to drive N channel MOSFET.

    Here, the controller HO pin is connected to push pull amplifier circuit and the output of this is connected to pulse transformer(in order to protect from high side switching) and the output of the pulse transformer is connected to gate of the N channel MOSFET. So, the remaining pins such as LO, SW (of the controller) is left over, where will these pins have connection? and what will happen if these pins are left unconnected?

  • 0 in reply to Swetha Revanna
    TI__Mastermind 30870 points

    Hello,

    OK from the schematic above, looks like you only need to drive Q1 and Q2 ref to Gnd, no need for Ho to be VCC above Vsw.  You are driving your power HS FET using a gate drive Transformer...So please do the following with the LM5116.

    1. Place a 10k from Lo to Gnd as it is not in use...

    2. Gnd the SW node

    3. Connect HB to VCC

    4. will still need a Series resistor on the low side of the free wheeling device (diode).

    4a.  Therefore place Rsense on Anode of D1.

    4b. Connect Rsense + to CSG

    4c. Connect Rsense - (Gnd) to CSG.

    Hope this helps?

    David Baba.

  • 0 in reply to David Baba
    Prodigy 50 points

    Hello,

    The Pin Vout says, need to be connected directly to the output but in my design, high voltage appears across it. What will happen if it is floating?

    Swetha

  • 0 in reply to Swetha Revanna
    TI__Mastermind 30870 points

    The Vout pin needs to be connected to Vout and it is rated to 100V, the pin should not be left floating.  The LM5116 is an Emulated current mode controller.  That is to say the current is not directly sensed but reconstructed using Vin, Vout and the current in the low side FET, using a sample and hold circuit.  You can tie the Vin and Vout pins to a lower voltage less than 100V.  The will create an error in the slope to the reconstructed current.