LTC1664
10
1664fa
operation
load can be successfully driven by inserting a 20Ω resis-
tor; a 2.2µF load needs only a 10Ω resistor. In either case,
larger values of resistance, capacitance or both may be
safely substituted for the values given.
Rail-to-Rail Output Considerations
In any rail-to-rail voltage output DAC, the output is limited
to voltages within the supply range.
If the DAC offset is negative, the output for the lowest
codes limits at 0V as shown in Figure 3b.
Similarly, limiting can occur near full-scale when the REF
pin is tied to V
CC
. If V
REF
= V
CC
and the DAC full-scale
error (FSE) is positive, the output for the highest codes
limits at V
CC
as shown in Figure 3c. No full-scale limiting
can occur if V
REF
is less than V
CC
– FSE.
Offset and linearity are defined and tested over the region
of the DAC transfer function where no output limiting can
occur.
1664 F03
INPUT CODE
(3b)
OUTPUT
VOLTAGE
NEGATIVE
OFFSET
0V
5120 1023
INPUT CODE
OUTPUT
VOLTAGE
(3a)
V
REF
= V
CC
V
REF
= V
CC
(3c)
INPUT CODE
OUTPUT
VOLTAGE
POSITIVE
FSE
Figure 3. Effects of Rail-to-Rail Operation On a DAC Transfer Curve. (a) Overall Transfer Function (b) Effect of Negative
Offset for Codes Near Zero-Scale (c) Effect of Positive Full-Scale Error for Input Codes Near Full-Scale When V
REF
= V
CC
