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LM20K Family PowerWise Synchronous Buck Regulator Slide 16

Here is an example of simultaneous sequencing. The value of R2 should generally be chosen to be less than 3.65Kohms to limit any errors due to the soft-start charging current for the slave supply to track (SS/TRK) pin. Once R2 is selected, R1 can be calculated by the given formula. The formula is derived from the fact that the voltage at the track pin should equal the feedback voltage of Vout2 when Vout1 is equal to the final value of Vout2. Note that the LM20xxx devices require approximately 200mV of overdrive on the SS/TRK pin to completely remove any effects the track voltage may have on the output. This required overdrive leads to the constraint that Vout2 must be less than 0.8 x Vout1.

PTM Published on: 2011-11-02