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What is VREF in uPC1093 data sheet, and how's VOUT calculated with VREF?

Latest Updated:11/01/2007

Question:

What is VREF (standard connection) listed in the uPC1093 data sheet, and how is VOUT calculated with VREF?

Answer:

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:

VOUT ≈ VREF (1 + R1/R2)


This can also be easily visualized using law of dividing voltage.

VOUT:VREF = (R1 + R2):R2
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.

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