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LM5164-Q1: Stop SW output for 1-2 seconds on LM5164-Q1

Motoyasu Hattori
Genius 9055 points
Part Number: LM5164-Q1
Other Parts Discussed in Thread: LM5146-Q1

Hi, 

My customer designs DCDC with LM5164-Q1.  However, after staring FANs, LM5164-Q1 stopped SW output for 1 - 2 seconds.  WHY does this phenomena occur?   Please let us know how to resolve this.

Spec is as follows.

Input : DC 73V
Output : 12V
Load : DC FAN x 2

Phenomena:

  1. power-up and output 12V on LM5146-Q1.
  2. Start DC FANs
  3. After 1-2 seconds, SW output is stopped and decrease output voltage.
  4. After 1-2 seconds, LM5146-Q1 re-starts SW output and output is returned (12V).
  5. Then LM5146-Q1 keep working correctly.

Schematics is as follows:

Thanks and best regards,
M.HATTORI.

  • 0
    TI__Mastermind 25590 points

    Hattori-san,

    • The input capacitance is insufficient. Try increasing CIN to at least 2.2uF
    • The output capacitance is very large. Try depopulating the 470uF output capacitor.

    If those do not help, please share the layout and please share waveforms showing VIN, VOUT, and SW over ~10 seconds (to see the entire event).

    -Sam