Re: trying to understand the REF pin on a DAC

John Popelish wrote:
John Popelish wrote:
kasterborus@xxxxxxxxx wrote:
Can someone explain what the REF pin on my DAC is for?
It's an input voltage reference that can be GND, Vdd-1.5 or nominally
2.048v at Vdd =5v.

What is this voltage used for?
How does it affect the output?

Some of the circuits I see have tied this to Vdd - which seems too
high.

(The chip is the 5618 12-bit serial DAC)

The ref pin generally scales the full scale output of the DAC. If you think of the digital value going into the DAC as a fraction that goes from zero to (2^12)/((2^12)-1), the output voltage will be that fraction multiplied by the reference voltage. In effect, the DAC is a one quadrant multiplier that that multiplies an analog voltage (the ref) by a digital fraction.

Sorry, that should have read
".../((2^12)+1)"

Arggg! Make that "((2^12)-1)/(2^12). The largest value the digital input can have for a 12 bit converter is (2^12)-1, but the converter has 2^12th states, one of those being zero.
.

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