Applications information – Rainbow Electronics MAX518 User Manual
Page 14
MAX517/MAX518/MAX519
2-Wire Serial 8-Bit DACs with
Rail-to-Rail Outputs
14
______________________________________________________________________________________
__________Applications Information
Power-Supply Bypassing and
Ground Management
Bypass V
DD
with a 0.1µF capacitor, located as close to
V
DD
and GND as possible. Careful PC board layout
minimizes crosstalk among DAC outputs, reference
inputs, and digital inputs. Figure 16 shows the suggest-
ed PC board layout to minimize crosstalk.
When using the MAX518 (or the MAX517/MAX519 with
V
DD
as the reference), you may want to add a noise fil-
ter to the V
DD
supply (Figure 17) or to the reference
input(s) (Figure 18), especially in noisy environments.
The reference input’s bandwidth exceeds 1MHz for AC
signals, so disturbances on the reference input can
easily affect the DAC output(s).
The maximum input current for a single reference input
is V
REF
/16k
Ω = I
REF
(max). In Figure 17, choose R
F
so
that changes in the reference input current will have lit-
tle effect on the reference voltage. For example, with R
F
= 6
Ω, the maximum output error due to R
F
is given by:
6
Ω x I
REF
(max) = 1.9mV or 0.1LSB
In Figure 18, there is a voltage drop across R
F
that
adds to the TUE. This voltage drop is due to the sum of
the reference input current (V
REF
/16k
Ω maximum), sup-
ply current (6mA maximum), and the amplifier output
current (V
REF
/R
LOAD
). Choose R
F
to limit this voltage
drop to an acceptable value. For example, with a 10k
Ω
load, you can limit the error due to R
F
to 0.5LSB
(9.8mV) by selecting R
F
so that:
R
F
= V
RF
/ I
RF
≤ 9.8mV / (5V / 16kΩ + 6mA +
5V / 10k
Ω)
R
F
≤ 1.4Ω
OUT1
REF0
N.C.
REF1
OUT0
N.C.
N.C.
GND
SYSTEM GND
Figure 16. PC Board Layout for Minimizing MAX519 Crosstalk
(bottom view)
Figure 17. Reference Filter When Using V
DD
as a Reference
MAX518
R
F
C
F
0.1
µF
V
DD
+5V
MAX517
MAX519
REF_
R
F
C
F
0.1
µF
V
DD
+5V
Figure 18. V
DD
Filter When Using V
DD
as a Reference