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  • TI Thinks Resolved

LM5017: LM5017 VCC bypass voltage

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Replies: 5

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Part Number: LM5017

Hello Mr. Xiang Fang and Wei Liu,

Kindly confirm the LM5017 VCC bypass voltage. Conflict arises from LM5017 datasheet & your application note on LM5017

The "section 7.3.2 VCC Regulator" in LM5017-datasheet viz. TI document SNVS783J; suggests VCC bypass voltage as 8.55-13V

Whereas "Step 1 - Determine the primary-side output" in your app-note, quoted below, suggests VCC bypass voltage as 7.8V
www.edn.com/.../Product-How-to--Fly-Buck-adds-well-regulated-isolated-outputs-to-a-buck-without-optocouplers-

  • Luck luck,

    The electrical characteristics table of the datasheet gives the true value - 6.25V min, 7.6V typ, 8.55V max.

    Section 7.3.2 refers to driving a voltage on VCC externally.

    -Sam

  • In reply to Samuel Jaffe:

    Objective is to drive voltage on VCC externally from Vpri. That means it should exceed 8.55V, the max one and NOT 7.8V, right !
  • In reply to luck luck:

    The min, typ, and max specs are for the internal LDO. These are the min, typ, and max voltages you would expect if you did not drive an external voltage.

    The spec you are looking for is the Absolute Maximum Rating (section 6.1) for VCC to RTN which is 13V. You can apply an external voltage but the part may become damaged if the VCC voltage exceeds 13V.

    -Sam
  • In reply to Samuel Jaffe:

    In other words, external Vpri < 8.5v won't be able to drive the internal LDO, right !

    LDO damage from Vpri > 13v is obvious, agree !
  • In reply to luck luck:

    Yes, we are on the same page now.

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