LTC1661 Linear Technology, LTC1661 Datasheet - Page 9

• Manufacturer Part Number: LTC1661
• Description: Micropower Dual 10-Bit DAC in MSOP
• Manufacturer: Linear Technology

OPERATIO
Voltage Outputs
Each of the rail-to-rail output amplifiers contained in the
LTC1661 can typically source or sink up to 5mA
(V
of either supply when unloaded and have an equivalent
output resistance of 85 (typical) when driving a load to
the rails. The output amplifiers are stable driving capaci-
tive loads up to 1000pF.
A small resistor placed in series with the output can be
used to achieve stability for any load capacitance. A 1 F
load can be successfully driven by inserting a 20 resistor
in series with the V
resistor, and a 10 F electrolytic capacitor can be used
without any resistor (the equivalent series resistance of
the capacitor itself provides the required small resis-
tance). In any of these cases, larger values of resistance,
capacitance or both may be substituted for the values
given.
CC
= 5V). The outputs swing to within a few millivolts
NEGATIVE
Figure 2. 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
OFFSET
VOLTAGE
OUTPUT
0V
U
OUT
pin. A 2.2 F load needs only a 10
INPUT CODE
(b)
VOLTAGE
OUTPUT
0
INPUT CODE
V
REF
512
(a)
= V
Rail-to-Rail Output Considerations
In any rail-to-rail DAC, the output swing 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 2b.
Similarly, limiting can occur near full scale when the REF
pin is tied to V
(FSE) is positive, the output for the highest codes limits at
V
if V
Offset and linearity are defined and tested over the region
of the DAC transfer function where no output limiting can
occur.
CC
CC
REF
as shown in Figure 2c. No full-scale limiting can occur
is less than V
1023
CC
. If V
REF
CC
– FSE.
V
= V
REF
INPUT CODE
= V
CC
(c)
CC
and the DAC full-scale error
LTC1661
REF
OUTPUT
VOLTAGE
POSITIVE
FSE
= V
1661 F02
CC
9