Rainbow Electronics MAX5121 - Manual (Page 17)

MAX5120/MAX5121
+3V/+5V, 12-Bit, Serial Voltage-Output DACs
with Internal Reference
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TO OTHER
SERIAL DEVICES
MAX5120
MAX5121
DIN
SCLK
CS
MAX5120
MAX5121
DIN
SCLK
CS
MAX5120
MAX5121
DIN
I II III
SCLK
CS
DIN
SCLK
CS1
CS2
CS3
Figure 13. Multiple Devices Share One Common Digital Input (DIN)
DAC
OUT
MAX5120
MAX5121
10k
26k
OS
REF
R
0.6384R
V DD
DGND AGND
+5V/+3V
AC
REFERENCE
INPUT
500mVp-p
MAX495
+5V/+3V
Figure 14. External Reference with AC Components
Using an External Reference
with AC Components
The MAX5120/MAX5121 have multiplying capabilities
within the reference input voltage range specifications.
Figure 14 shows a technique for applying a sinusoidal
input to REF, where the AC signal is offset before being
applied to the reference input.
Power-Supply and Bypassing
Considerations
On power-up, the input and DAC registers are cleared
to either zero (RSTVAL = DGND) or midscale (RSTVAL
= V DD ). Bypass the power supply with a 4.7µF capaci-
tor in parallel with a 0.1µF capacitor to AGND. Minimize
lead lengths to reduce lead inductance.
Layout Considerations
Digital and AC transient signals coupling to AGND can
create noise at the output. Connect AGND to the high-
est quality ground available. Use proper grounding
techniques, such as a multilayer board with a low-
inductance ground plane. Wire-wrapped boards and
sockets are not recommended. If noise becomes an
issue, shielding may be required.