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LM5166: LM5166 PSpice Transient Model works without GND

Wilfried Hermann
Prodigy 60 points
Part Number: LM5166
Other Parts Discussed in Thread: LM22680

Hello,
I have used the model in LTspice.
In normal operation the model works very well.
Now I wanted simulate the device as an inverting buck-boost converter according to snva856a.pdf chapter 5.
But this does not work.
After some searching I found out, that a "normal" simulation does not work, if the simulation GND is not connected to the GND-PIN, but somewhere else in the network.

Apparently in the simulation file the network "0" is used as absolute GND and is not assigned to the GND PIN of the device.
How can I correct this? (Search " 0 " and replace with " GND " doesn't work.

So you don't need to connect anything to the PIN GND or PAD in the simulation - the circuit still runs in the simulation, but only in a "normal" buck-simulation referred to simulation-GND

B.R.
Wilfried

  • 0
    TI__Guru 58175 points

    Hello

    Please take a look at figure 8 in the attached app note for a way

    to simulate the IBB using an ordinary buck model.

    Thanks

    1537.snva856a.pdf

  • 0 in reply to Frank De Stasi
    Prodigy 60 points

    Hi Frank,

    I wrote:
    "Now I wanted simulate the device as an inverting buck-boost converter according to snva856a.pdf chapter 5."

    So it is not the problem how to do it, but the problem is, that the model doesn't work.

    To get a negative voltage you have to place the ground behind the inductance.
    If you do it this way, the model will not work anymore, because they use the net "0" inside the model, which is always ground.

    (Therefore the model can be simulated without GND connection, because GND is connected via the net "0" within the model - it's funny)

    Due to this error the GND connection cannot float and never become a negative voltage.

    So you can't simulate the IBB according to snva856a with this model.

    The model would have to be modified in such a way that all nets "0" and similar must be assigned to the actual GND pin in the model.


    BR
    Wilfried

  • 0 in reply to Wilfried Hermann
    TI__Guru 58175 points

    Hello

    Using the method shown in the app note, you just connect the input supply between the input of the regulator and the output.

    You don't kneed to change the ground connections.

    Of course, this is not an exact representation of an inverting regulator.  However, it is the same way that you would use a buck

    as an IBB in an application.

    Unfortunately, we do not have an IBB model for this device with a "floating" ground.

    Thanks

  • 0 in reply to Frank De Stasi
    Prodigy 60 points

    Hello,

    I want to simulate a circuit with positive and negative supply. Both with the LM5166 and corresponding control circuits.
    This will not work if a 2nd LM5166 is added.

    I have found  that this problem also exists with other switching regulators (LM22680), which we also use as BB and IBB.

    Since we are now redesigning our product, I would like to be able to simulate this in advance.

    I will probably use the LTC3630A, as this model can be simulated as BB and IBB without any problems.
    It's a pity that the TI models don't offer this.

    BR
    Wilfried