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Forum Post: Webench phase margin

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I need a boost converter:  4~5 Volt in, 14 Volts out @ 100 mA for a battery powered application.  Webench suggested an LM2735X based circuit with an unshielded inductor and 45 degree phase margin.  I selected a very similar but slightly larger shielded inductor.  The phase margin went to 15 degrees.  I changed back to the original inductor and the phase margin went to 14 degrees!

The Bode plots seemed to be nonsense.  The original had only -20 dB of gain at 1 Hz.  with the shielded inductor.  With the new inductor the phase is between -100 and -200 degrees out to 100 kHz, then dived to -360 degrees and suddenly spiked to about 0 degrees at 900 kHz.

Is the simulation working correctly?  If so, how can I change to a shielded inductor and maintain an acceptable phase margin?


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