TLC7226C_15 Datasheet, PDF (10/24 Pages) Texas Instruments – QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS

TLC7226C, TLC7226I, TLC7226M
ą
QUADRUPLE 8ĆBIT DIGITALĆTOĆANALOG CONVERTERS
ą
SLAS060F − JANUARY 1995 − REVISED APRIL 2009
PRINCIPLES OF OPERATION
linearity, offset, and gain error using single-ended power supplies
When an amplifier is operated from a single power 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, with a negative voltage offset, attempts to drive the output to a negative voltage. However,
because the most negative supply rail is ground, the output cannot be driven to a negative voltage.
So when the output offset voltage is negative, the output voltage remains at zero volts until the input code value
produces a sufficient output voltage to overcome the inherent negative offset voltage, resulting in a transfer
function shown in Figure 8.
Output
Voltage
0V
Negative
Offset
DAC Code
Figure 8. Effect of Negative Offset (Single Power Supply)
This negative offset error, not the linearity error, produces the breakpoint. The transfer function would have
followed the dotted line if the output buffer could be driven to a negative voltage.
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 are adjusted out or accounted for in some way. However, single power 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 negative offset.
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