Datasheet

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REFERENCE INPUTS
2kW
96kW
+5V
ExternalReference
+5.0000V
OPA2350
2200pF
2200pF
1000pF
1000pF
SCLK
SDI
LDAC
AGND
AV
DD
V -S
REFL
1
2
3
4
5
6
DAC8881
V -S
REFH
V
OUT
R
FB
V -F
REFL
V F
REF
H-
NC
7 8 9
10 11 12
2kW
50W
50W
+4.900V
+0.100V
1.0
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
1.0
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
LE(LSB)
DLE(LSB)
0 8192 16384 24576 32768
DigitalInputCode
40960 49152 57344 65536
+25 C°
+25 C°
1.0
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
1.0
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
LE(LSB)
DLE(LSB)
0 8192 16384 24576 32768
DigitalInputCode
40960 49152 57344 65536
+25 C°
+25 C°
DAC8881
SBAS422A – JULY 2007 – REVISED SEPTEMBER 2007
The reference high input, V
REFH
, can be set to any voltage in the range of 1.25V to AV
DD
. The reference low
input, V
REFL
, can be set to any voltage in the range of – 0.2V to +0.2V (to provide a small offset to the output of
the DAC8881, if desired). The current into V
REFH
and out of V
REFL
depends on the DAC code, and can vary from
approximately 0.5mA to 1mA in the gain = 1X mode of operation. The reference high and low inputs appear as
varying loads to the external reference circuit. If the external references can source or sink the required current,
and if low impedance connections are made to the V
REFH
and V
REFL
pins, external reference buffers are not
required. Figure 67 shows a simple configuration of the DAC8881 using external references without force/sense
reference buffers.
Kelvin sense connections for the reference high and low are included on the DAC8881. When properly used with
external reference buffer op amps, these reference Kelvin sense pins ensure that the driven reference high and
low voltages remain stable versus varying reference load currents. Figure 69 shows an example of a reference
force/sense configuration of the DAC8881 operating from a single analog supply voltage. Both the V
REFL
and
V
REFH
reference voltages are set to levels of 100mV from the DAC8881 supply rails, and are derived from a +5V
external reference. Figure 71 and Figure 70 illustrate the effect of not using the reference force/sense buffers to
drive the DAC8881 V
REFL
and V
REFH
pins. A slight degradation in INL and DNL performance of approximately 0.1
LSB may be seen without the use of the force/sense buffer configuration.
Figure 69. Buffered References (V
REFH
= +4.900V and V
REFL
= 100mV)
Figure 70. Linearity and Differential Linearity Error Figure 71. Linearity and DifferentialLinearity Error
for Figure 67 without Reference Buffers for Figure 69 with Reference Buffers
Copyright © 2007, Texas Instruments Incorporated Submit Documentation Feedback 25
Product Folder Link(s): DAC8881