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I am using R1276S001A-E2-FE to convert my 24 V supply to 3.3 V to power my microcontroller.

In order to do the conversion properly I need to choose the output capacitor. I see there are three ways to do so according to the datasheet (page 12). Which one should I follow?

I have never used a swicthing regulator before. Could someone explain the MODE Pin-10 (page-18) operation?

I don't see any necessity for it for my project, so I have not connected it to Vcc.

Does my capacitor equation depend on the MODE I use?

VFM

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  • \$\begingroup\$ You must estimate Rout range for stability then follow p 10,11 to maximize phase margin \$\endgroup\$
    – D.A.S.
    Commented Jul 25, 2022 at 11:01

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There are no three separate ways, the capacitance must be chosen in a way that is suitable with all the equations.

If you don't use the VFM mode then you don't have to make sure the capacitor fits the VFM mode requirements.

But VFM mode is disabled by setting MODE high. It is also unknown why you don't want to use automatic VFM mode to have better efficiency at low loads, but it is possible to use forced PWM.

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  • \$\begingroup\$ Thanks for the answer. That clears my first confusioni. Now, As far i understood, if connect MODE to low, it shold switch automatically between two modes. is this the right connection? I added a picture for that(ignore R40). \$\endgroup\$
    – rafi
    Commented Jul 25, 2022 at 11:31
  • \$\begingroup\$ I suppose if we connect the MODE pin to VCC, it would be in forced PWM mode as the Application circuit shows. \$\endgroup\$
    – rafi
    Commented Jul 25, 2022 at 12:17

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