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UCC27714: why connect the EN_NC to ground, still have HO, LO output in simulation

gang yu
Prodigy 10 points
Part Number: UCC27714


hello,

i use UCC27714 in my product, to check the performance, i make simulation in Pspice for TI.

But why we have output LO HO, even when EN_NC are connected to ground.

It is not like the description in the datasheets.

In the datasheets, it is clear the output will be blocked when EN_NC are grounded.

I check the demo model of the software, the test fixture model, the same finding.

Any explanation to this ?

Thanks.

  • 0
    TI__Genius 9451 points

    Hello,

    My colleague who supports this product is currently out of the office. He will return tomorrow and will respond at that time. 

    Thank you for your patience. 

    Best regards,

    Leslie

  • 0 in reply to Leslie Marquez
    TI__Mastermind 23215 points

    Hello Gang,

    As you mention the EN pin pulled low (relative to VSS) should disable the LO and HO driver outputs, even with LI and HI inputs being active.

    Do you have some simulation plots to show this behavior? Along with your simulation circuit? Can you provide the plots of the behavior you mention?

    Regards,

  • 0 in reply to Richard Herring
    Prodigy 10 points

    Hello, this is descriptions in the datasheets of UCC27714. Please check it in the table "Pin Functions".

    I don't find this behavior in simulation, that confuses me. That is the reason I raise this question.

    EN/NC 4 I Enable input for high-side and low-side driver. This pin biased LOW, disables both HO and
    LO regardless of HI and LI state, This pin biased high or floating enables both HO and LO.

    But in simulation, i don't find this behavior. Even with your text fixture model, provided by TI, i ground the EN_NC, I still have output of HO, LO.

    Can you check this ?

    Thanks.

  • 0 in reply to gang yu
    TI__Mastermind 23215 points

    Hello Gang,

    Can you confirm if you are using the UCC27714 Pspice transient model, or the UCC27714 Unencrypted Pspice transient model. I assume you downloaded this from the design tools and simulation page. 

    I will look to download the model and confirm, if you can confirm the model you see the issue. 

    Regards,

  • 0 in reply to Richard Herring
    Prodigy 10 points

    Hello, I confirm I use UCC27714 Pspice transient model.

    I installed the software Pspice for TI, and get this model from the Texas Instruments in the software.

    Considering the software is provided by TI, and also the library provided by TI. I think the model should match the datasheets. Before I launched PCB, the important thing is I need to confirm which I can trust, the simulation model or the data sheets.

    We want to use the EN_NC function in our design. 

    You can double check it.

    Thanks.

  • +1 in reply to gang yu
    TI__Mastermind 23215 points

    Hello Gang,

    Thank you for confirming the model you are using. It will take one or two days for someone on our team to set up and confirm the simulation you are mentioning.

    I do have some questions on the simulation schematic. On the source for LI and HI I see a PW of 45ns and period of 250ns. is that correct?  A 250ns period is 4MHz which is quite a bit beyond a recommended frequency range of this part. Also 45ns is a fairly low PW for this part.

    Can you try a PW of 500ns and period of 2us (which is 500kHz). Just to confirm if you get similar results?

  • 0 in reply to gang yu
    TI__Mastermind 23215 points

    Hello Gang,

    Regarding the question on the model or the datasheets, the part has been qualified and is production tested regarding the enable function disabling the driver outputs per the datasheet parameter table.

    We did find/confirm however, that the model does seem to have some issue with the enable function as you describe. For a workaround in simulation. You can add external and gates to the LI and HI inputs and have the driver disabled with a common enable input to the two and gates.

    We will look into the issue with the model, but this will not be a fast turn around.

    Regards, 

  • 0 in reply to Richard Herring
    Prodigy 10 points

    OK, clear, thanks for your answer to confirm.

    Have a great day.