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TPS7H1101A-SP: Soft Start

Robert Ortega
Prodigy 60 points
Part Number: TPS7H1101A-SP
Other Parts Discussed in Thread: TPS50601A-SP

Hello,

I am using the TPS7H1101A-SP soft start, but when simulating with the PSpice model I am not getting the expected results. According to the soft start equation. 

Using Css = 15nF would result in tss= 3.63ms.

However, after setting the enable to high the output voltage ramp does not start until after ~1.45ms delay. 

Where is this delay coming from?

Below is the schematic and waveforms.

  • +1
    TI__Expert 8090 points

    Hi Robert,

    The ~1.45ms comes from an internal RC delay in the model. This is mean to emulate the Enable terminal turn-on delay - see the screenshot below from the datasheet.

    Let me know if there's anything else I can help clarify.

    Thanks,

    Sarah

  • 0 in reply to Sarah Koch
    Prodigy 60 points

    Hi Sarah,

    Thank you for the information.

    Is there a min value for this delay? I do not see it on the screenshot.
    I am using the TPS7H1101A-SP along with the TPS50601A-SP. My goal is to have to have both enabled at the same time and the output voltage track with each other.

    Thanks,

    Robert

  • +1 in reply to Robert Ortega
    TI__Expert 8090 points

    Hi Robert,

    Unfortunately the minimum is not spec'd in the datasheet so I don't have data to guarantee a value that would account for temp, radiation, and operating conditions across the device lifetime. That said, there is some data available in the TID Report for this device that we can reference for room temp pre/post-radiation values. If you search the document for "20.0_" it will show the different test data for the TEN spec for a sample of units. We ship these reports with every order.

    The distribution is actually fairly tight, so part-to-part variation at least shouldn't play a major role. This should at least give you something solid to start with and then tune later if needed.

    Let me know if there is anything I can help with or clarify.

    Thanks,

    Sarah