VREF is the input voltage of the REF pin, and is the reference voltage. The output voltage is led by VREF and two external resistors.
The following relationships exist as a result.
VOUT = VREF + Voltage dropped by R1
VOUT = VREF + (VREF/R2 + IREF) × R1
VOUT =VREF (1 + R1/R2) + IREF × R1
Here, IREF being a current of the µA order, it is possible to posit the following equation by omitting IREF × R1:
This can also be easily visualized using law of dividing voltage.
VOUT × R2 = VREF × (R1 + R2)
VOUT = VREF × (R1 + R2)/R2 = VREF × (1 + R1/R2)
VREF becomes constant at 2.495 V (typ.), so that the output voltage (VOUT) can be changed (recommended operation condition: Min. VREF to Max. 36 V) depending on the ratio of R1 and R2.
When using the uPC1093 as a 2.5 V constant power supply, the following connection with R1 = 0, R2 = ∞ (open) is used.