TLC7225 Datasheet, PDF (19/22 Pages) Texas Instruments – QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS

TLC7225C, TLC7225I
QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS
SLAS109B – OCTOBER 1996 – REVISED FEBRUARY 2001
APPLICATION INFORMATION
linearity, offset, and gain error using single-ended supplies
When an amplifier is operated from a single supply, the voltage offset can still be either positive or negative. With
a positive offset, the output voltage changes on the first code change. With a negative offset the output voltage
may not change with the first code depending on the magnitude of the offset voltage.
The output amplifier attempts to drive the output to a negative voltage. However, since the most negative supply
rail is ground, the output cannot drive below ground.
So with this output offset voltage, the output voltage remains at zero until the input-code value produces a
sufficient output voltage to overcome the inherent offset voltage, resulting in a transfer function shown in
Figure 18.
Output
Voltage
0V
Negative
Offset
DAC Code
Figure 18. Effect of Negative Offset (Single Supply)
This offset error, not the linearity error, produces this breakpoint. The transfer function would have followed the
dotted line if the output buffer could drive below ground.
For a DAC, linearity is measured between zero-input code (all inputs 0) and full-scale code (all inputs 1) after
offset and full scale is adjusted out or accounted for in some way. However, single supply operation does not
allow for adjustment when the offset is negative due to the breakpoint in the transfer function. So the linearity
in the unipolar mode is measured between full-scale code and the lowest code, which produces a positive output
voltage.
The code is calculated from the maximum specification for the zero offset error.
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