SNVA406C May   2010  – January 2022 LM27402

 

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9.5 Soft-Start Capacitor, Css

A soft-start capacitor can be used to control the start-up time of the LM27402. The start-up time is estimated by the following equation:

Equation 9. GUID-FE2C0E01-3570-4D1E-988F-37E26F1DE015-low.gif

ISS is nominally 3 µA. For the evaluation board, the soft-start time has been designed to be approximately 10 ms, resulting in a Css capacitor value of 47 nF. The LM27402 defaults to a 1.28-ms start-up ramp time if Css is not used.