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I am using buck converter. 3.3V output & 2.5A part with 2.1MHz switching frequency.

I am powering my microcontroller with this 3.3V output. So, I'd like to find the output voltage tolerance of the buck converter.

Usually, to find the min and max output voltage of the converter, there would be some output voltage formula which would involve some resistors. So, I would take these resistor tolerances that would help me find the minimum and maximum output voltage.

Since, there are no feedback resistors in the the 3.3V output configuration, or any other formula, can someone tell me how to find the minimum and maximum output voltage for this part?

I am also using a 10uH part as inductor with 2x 10uF capacitor. Can someone also help me on how to calculate the output voltage and output ripple current? There are no calculated examples or formulas provided in the datasheet. Please help with the above.

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  • \$\begingroup\$ The error from internal tolerances must be defined in the datasheet. But dynamic error from step load changes depends on the whole circuit added. \$\endgroup\$ Jun 21 at 18:35
  • \$\begingroup\$ Thank you for the clarification. No tolerance or anything related to output voltage formula is included in the DS. Can you help? \$\endgroup\$
    – Newbie
    Jun 21 at 18:37
  • \$\begingroup\$ The Vfb has a 1.5% tolerance then add the tolerances of ratio divider. \$\endgroup\$ Jun 21 at 18:39
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    \$\begingroup\$ I am powering my microcontroller with this 3.3V output Microcontrollers are generally not fussy about their supply voltage. I work with MCUs that can operate from a supply voltage of 1.8 V up to 5.5 V. Can you explain why the tolerance on your 3.3 V is important at all? My point is that I would need a very special reason to not just program the buck converter to 3.3 V and use that. That 3.3 V will be accurate enough unless there's a special reason why that is not the case. \$\endgroup\$ Jun 21 at 18:44
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The datasheet lists 3.3V output min and max values on page 8, that's the FB voltage for your 3.3V regulator.

The output ripple will be dependent on if the load is light or heavy, as the chip can alter between PFM and PWM modes of operation. During light load in PFM mode, the ripple is usually higher than in PWM mode.

Formulas to calculate ripple due to output capacitance is on page 27. Basically, the ripple depends on capacitor ESR, capacitor capacitance, and the current used to charge and discharge the capacitor.

But like the datasheet mentions, usually the capacitor capacitance and ESR are more defined by load transient requirements, so the effect of ripple much less.

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