Datasheet

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ANALOG OUTPUT
LoadDACRegisters
SerialDataIn
Clock
SerialDataOut
+
0.1 Fm 1 Fm
+5V
ExternalReference
+5.0000V
V
OUT
1.8Vto5V
ResetDACRegisters
SDOSEL Chip-Select
SCLK
SDI
LDAC
AGND
AV
DD
V -S
REFL
(ThermalPad)
PDN
RST
USB/BTC
GAIN
RSTSEL
NC
1
2
3
4
5
6
18
17
16
15
14
13
DAC8881
IOV
DD
SDO DGND DV
DD
SDOSEL CS
24 23 22 21 20 19
V -S
REFH
V
OUT
R
FB
V
-F
REF
L
V -F
REFH
NC
R
W2
R
W1
7 8 9
10 11 12
+
0.1 Fm 1 Fm
DAC8881
SBAS422A – JULY 2007 – REVISED SEPTEMBER 2007
The DAC8881 offers a force and sense output configuration for the high open-loop gain output amplifier. This
feature allows the loop around the output amplifier to be closed at the load (as shown in Figure 68 ), thus
ensuring an accurate output voltage. The output buffer V
OUT
and R
FB
pins are provided so that the output op amp
buffer feedback can be connected at the load. Without a driven load, the DAC8881 output typically swings to
within 15mV of the AGND and AV
DD
supply rails. Because of the high accuracy of these DACs, system design
problems such as grounding and contact resistance become very important. A 16-bit converter with a 5V
full-scale range has a 1LSB value of 76 μ V. With a load current of 1mA, a series wiring and connector resistance
of only 80m Ω (R
W2
) causes a voltage drop of 80 μ V. In terms of a system layout, the resistivity of a typical
1-ounce copper-clad printed circuit board is 0.5m Ω per square. For a 1mA load, a 0.25mm wide printed circuit
conductor 25mm long results in a voltage drop of 50 μ V.
Figure 68. Analog Output Closed-Loop Configuration
(R
W1
and R
W2
represent wiring resistance)
24 Submit Documentation Feedback Copyright © 2007, Texas Instruments Incorporated
Product Folder Link(s): DAC8881