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TPS709: LTspice simulation with a model of TPS70950 with floating ground

Daisuke Kobuchi
Prodigy 20 points
Part Number: TPS709

Hello,

I ran a simulation with LTspice using a PSpice model of TPS70950 provided by TI.

I want to use this regulator with floating ground, so I used square-wave voltage source as the ground.

The schematic is as follows.

As a result of the simulation, the output voltage Vout is about the reversed ground voltage.

This output voltage does not change when changing the input voltage.

When the ground is connected to constant 0V source, the output voltage was 5V as the following figure. So, it worked well when the ground is not floating.

When I used LT1086-5 as a regulator with floating ground, it worked well as follows. 

I want to know if TPS70950 can be used for applications with a floating ground.

If there is any mistake in my schematic, please tell me.

  • 0
    TI__Mastermind 34975 points

    Hi Daisuke,

    The TPS709 can be used with a floating GND.  This type of application is quite common when powering high side gate drivers, for instance.  We are unable to help you troubleshoot the LTSpice simulation due to LTSpice license, unfortunately.  You can use Cadence for TI instead of LTSpice to simulate this and if you run into any issues, let us know.  But to answer your question, the TPS709 should work as you have drawn it just fine.  The LDO circuitry is just riding on top of a DC square wave, again this type of thing is common in industry.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 20 points

    Hi Stephen,

    Thank you for your advice.

    I installed PSpice for TI and ran a simulation under the same condition.

    But the result was almost the same when I ran a simulation in LTspice.

    Is there any wrong settings in the simulation?

    Sincerely,

    Daisuke

  • +1 in reply to Daisuke Kobuchi
    TI__Mastermind 34975 points

    Thanks Daisuke, upon further review of the model it looks like many nodes are internally tied to GND.  This prevents the model from simulating as you expect in this application but this is purely a model limitation.  As I previously noted, the LDO will simply be riding on top of a square wave (like a high side gate driver application) so it should work in an actual application.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 20 points

    Thanks Stephen.

    I plan to use this LDO in a high side gate driver application, so your comment is very helpful.

    Thank you so much.