12-Bit Serial Daisy-Chain D/A Converter
FIGURE 11. DIGITAL INPUT PROTECTION
8143
Equivalent Circuit Analysis
Figures 12 and 13 show equivalent circuits for the 8143 internal DAC with all bits LOW and HIGH, respectively. The
reference current is switched to IOUT2 when all data bits are LOW, and to IOUT1 when all bits are HIGH. The ILEAK-
AGE current source is the combination of surface and junction leakages to the substrate. The 1/4096 current source
represents the constant 1-bit current drain, through the ladder’s terminating resistor.
Output capacitance is dependent upon the digital input code. This is because the capacitance of a MOS transistor
changes with applied gate voltage. This output capacitance varies between the low and high values.
FIGURE 12. EQUIVALENT CIRCUIT (ALL INPUTS LOW)
07.23.03 REV 3
All data sheets are subject to change without notice 11
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