I have been designing a digitally adjustable step-down voltage regulator. Mainly because of the availability and price I chose:

I followed the datasheet and created the following schematic: enter image description here

My plan is to use a DAC integrated in the MCU (ATSAMD21E18A) as shown in the schematic to adjust the output voltage from 1.5 V to 5 V using a 0.. 3 V DAC signal.

My concern is, that with a setup like this, I could "force" (introduce a specific voltage to the feedback pin) the regulator to output voltages like 5.1 V. Could this damage the regulator, or will it just cap on a 100% duty cycle without affecting performance?

VCC is approximately 5.. 5.5 V

  • \$\begingroup\$ Section 4.3 details exactly what happens with 100%. \$\endgroup\$
    – Kartman
    Commented Jan 18, 2022 at 10:06
  • \$\begingroup\$ But if I understand that section correctly, it mainly talks about an input/output voltage difference. Meaning that it can ALMOST (excluding the ohmic losses) output 5V when 5V is on the input. My question is more focused on what would happen if using the feedback resistive network, I would set a voltage higher than the input. It is hard for me to express my thought, to give an example VFB=0.8V and R1:R2 = 10:1 (exaggerating), basically telling the regulator to try and set an output voltage of 8.8V. \$\endgroup\$ Commented Jan 18, 2022 at 10:17

1 Answer 1


This is a buck regulator, it's physically impossible for it to output a higher voltage than its input voltage. When you request it to output a voltage that it can't produce, it will drop out of regulation and go to 100% duty cycle. It won't get damaged and will continue to operate normally once you request a "sane" voltage again.


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