HX711 - Analog Supply Regulator
It's a run-of-the-mill "3 terminal" positive voltage regulator, EXCEPT the "series pass element" (in this case, a PNP transistor) is not integrated but must be supplied externally.

The positive (unregulated) INPUT voltage is applied to VSUP and the PNP's emitter.

The positive (now regulated!) OUTPUT voltage is "taken" from the PNP's collector.

The regulator itself does basically 1 thing: It "samples" the voltage applied to the "VFB" pin, compares it to some internal voltage that it generates within itself, and depending upon whether the sampled VFB voltage is "too high" or "too low", decides to draw (less) or (more) current into its "output" pin "BASE".  Basically, if VFB is too low, the chip will PULL more current into its BASE pin, turning the external PNP transistor "ON" harder, thus raising the output voltage to proper level.  Similarly, if VFB is too high, the chip will PULL less current into BASE, the PNP will turn "OFF" a little, and the output voltage will drop.

By choosing the resistor-divider ratio between the PNP collector (the regulated voltage output) and VFB, you can vary the output voltage to whatever value you need (within reason) so long as it's not too close to VSUP nor too low (i.e. too close to ground).

The voltage that the chip compares the VFB input voltage pin "to" is, from the datasheet, called "V_BG" (also "Reference Bypass") and is 1.25V nominal.