Datasheet

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
DAC9881
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
NOTE:V canbeconnectedtoAGNDifV isnotbiased.
REFL REFL
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
LE(LSB)
0 32768 65536 98304 131072
DigitalInputCode
163840 196608 229376 262144
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
DLE(LSB)
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
LE(LSB)
0 32768 65536 98304 131072
DigitalInputCode
163840 196608 229376 262144
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
DLE(LSB)
DAC9881
www.ti.com ......................................................................................................................................................... SBAS438A – MAY 2008 – REVISED AUGUST 2008
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 DAC9881, 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
variable 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 65 shows a simple configuration of the DAC9881 using external references without force and
sense reference buffers.
Kelvin sense connections for the reference high and low are included on the DAC9881. 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 67 shows an example of a reference
force and sense configuration of the DAC9881 operating from a single analog reference voltage. Both the V
REFL
and V
REFH
reference voltages are set to levels of 100mV from the DAC9881 supply rails, and are derived from a
+5V external reference. Figure 68 illustrates the effect of not using the reference force and sense buffers to drive
the DAC9881 V
REFL
and V
REFH
pins. Figure 69 shows the improvement when using the reference buffers. A slight
degradation in INL and DNL performance is seen without the use of the force and sense buffer configuration.
Figure 67. Buffered References (V
REFH
= +4.900V and V
REFL
= 100mV).
Figure 68. Linearity and Differential Linearity Error Figure 69. Linearity and Differential Linearity Error
for Figure 65 without Reference Buffers for Figure 67 with Reference Buffers
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Product Folder Link(s): DAC9881