Datasheet
DAC8420
Rev. B | Page 18 of 24
is 16 mV. Thus, the best single-supply operation is obtained with
the output load connected to ground, so the output stage does not
have to sink current.
Like all amplifiers, the DAC8420 output buffers do generate
voltage noise, 52 nV/√Hz typically. This is easily reduced by
adding a simple RC low-pass filter on each output.
REFERENCE CONFIGURATION
The two reference inputs of the DAC8420 allow a great deal
of flexibility in circuit design. The user must take care, however,
to observe the minimum voltage input levels on VREFHI and
VREFLO to maintain the accuracy shown in the data sheet.
These input voltages can be set anywhere across a wide range
within the supplies, but must be a minimum of 2.5 V apart in
any case (see
Figure 30). A wide output voltage range can be
obtained with ±5 V references, which can be provided by the
AD588 as shown in Figure 33. Many applications utilize the
DACs to synthesize symmetric bipolar waveforms, which
require an accurate, low drift bipolar reference. The
AD588
provides both voltages and needs no external components.
Additionally, the part is trimmed in production for 12-bit
accuracy over the full temperature range without user calibra-
tion. Performing a clear with the reset select CLSEL high allows
the user to easily reset the DAC outputs to midscale, or 0 V in
these applications.
When driving the reference inputs VREFHI and VREFLO, it is
important to note that VREFHI both sinks and sources current,
and that the input currents of both are code dependent. Many
voltage reference products have a limited current sinking
capability and must be buffered with an amplifier to drive
VREFHI in order to maintain overall system accuracy. The
input VREFLO, however, has no such requirement.
89161514121110
DAC8420
1
5 9 10 8 12 11 13
3467
1
14
15
2
16
0.1µF
0.1µF
+15V
SUPPLY
–15V
SUPPLY
SYSTEM
GROUND
+5V
–5V
A3
A4
+V
S
–V
S
AD588
R4
R5
R6
R2
R1
R
B
R3
1µF
A1
A2
DAC A
DAC B
DAC C
DAC D
4
5
DIGITAL
CONTROLS
GND
DIGITAL INPUTS
VREFHI
+5V
VREFLO
–5V
2
3
6
7
+15V SUPPLY
0.1µF
–15V SUPPLY
0.1µF
VOUTA
VOUTB
VOUTC
VOUTD
00275-033
Figure 33. ±10 V Bipolar Reference Configuration Using the AD588