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TPS7H5001-SP: Clarification on 45% Margin in TPS7H5001 Primary Current Sensing

KUPPUSWAMY NAIDU
Prodigy 20 points
Part Number: TPS7H5001-SP


Hello Team,

While reviewing the TPS7H5001 application note (Section 9.2.2.12), I noticed that the sense resistor ILIM on the primary is set with a ~45% margin above the nominal primary current.

Could you please clarify:

  1. What factors are considered when choosing this 45% margin?

  2. Does this margin imply that the transformer and other magnetic components need to be designed to handle currents up to this margin?

  3. How does this margin relate to thermal, transient, and peak current considerations in the primary winding and MOSFETs?

I would appreciate a detailed explanation of the rationale behind this margin and its impact on magnetics and system design.

Thank you.

  • 0
    TI__Expert 6951 points

    Hello Kuppuswamy,

    The design of any converter using the TPS7H5001-SP PWM controller is extremely flexible, and the current limit can be set using CS_ILIM to an extremely wide range. The example provided in section 9.2.2.12 of the device datasheet is simply an example, and is not intended to be a requirement for system designs using the TPS7H5001-SP.

    Current limit for your application should be selected based on your system requirements and capabilities, and similarly the margin on the current limit should also be selected based on your system requirements and capabilities.

    As for your questions on passive / system design, again due to the flexibility of the TPS7H5001-SP device and the individuality of converter designs, magnetic and FET selections as they relate to the selected current limits are often based on customer design rules or requirements. The safest approach would of course be to select FETs and magnetics that are rated up to the selected current limit, but there are many design philosophies and rules that could be followed.

    Thanks,

    Andy