Datasheet

MAX5891
Grounding, Bypassing, and Power-Supply
Considerations
Grounding and power-supply decoupling strongly influ-
ence the MAX5891 performance. Unwanted digital
crosstalk coupling through the input, reference, power
supply, and ground connections affects dynamic per-
formance. High-speed, high-frequency applications
require closely followed proper grounding and power-
supply decoupling. These techniques reduce EMI and
internal crosstalk that can significantly affect the
MAX5891 dynamic performance.
Use a multilayer printed circuit board (PCB) with sepa-
rate ground and power-supply planes. Run high-speed
signals on lines directly above the ground plane. Keep
digital signals as far away from sensitive analog inputs
and outputs, reference input sense lines, common-
mode inputs, and clock inputs as practical. Use a sym-
metric design of clock input and the analog output lines
to minimize 2nd-order harmonic distortion components,
thus optimizing the DAC’s dynamic performance. Keep
digital signal paths short and run lengths matched to
avoid propagation delay and data skew mismatches.
The MAX5891 requires five separate power-supply
inputs for analog (AV
DD1.8
and AV
DD3.3
), digital
(DV
DD1.8
and DV
DD3.3
), and clock (AV
CLK
) circuitry.
Decouple each AV
DD3.3
, AV
DD1.8
, AV
CLK
, DV
DD3.3
, and
DV
DD1.8
input with a separate 0.1µF capacitor as close
to the device as possible with the shortest possible con-
nection to the respective ground plane (Figure 7).
Connect all of the 3.3V supplies together at one point
with ferrite beads to minimize supply noise coupling.
Decouple all five power-supply voltages at the point they
enter the PCB with tantalum or electrolytic capacitors.
Ferrite beads with additional decoupling capacitors
forming a pi network can also improve performance.
Similarly, connect all 1.8V supplies together at one point
with ferrite beads.
The analog and digital power-supply inputs AV
DD3.3
,
AV
CLK
, and DV
DD3.3
allow a 3.135V to 3.465V supply
voltage range. The analog and digital power-supply
inputs AV
DD1.8
and DV
DD1.8
allow a 1.71V to 1.89V
supply voltage range.
The MAX5891 is packaged in a 68-pin QFN-EP pack-
age with exposed paddle, providing optimized DAC AC
performance. The exposed pad must be soldered to
the ground plane of the PCB. Thermal efficiency is not
the key factor, since the MAX5891 features low- power
operation. The exposed pad ensures a solid ground
connection between the DAC and the PCB’s ground
layer.
The data converter die attaches to an EP lead frame
with the back of this frame exposed at the package
bottom surface, facing the PCB side of the package.
This allows for a solid attachment of the package to the
PCB with standard infrared (IR) reflow soldering tech-
niques. A specially created land pattern on the PCB,
matching the size of the EP (6mm x 6mm), ensures the
proper attachment and grounding of the DAC. Place
vias into the land area and implement large ground
16-Bit, 600Msps, High-Dynamic-Performance
DAC with LVDS Inputs
12 ______________________________________________________________________________________
MAX5891
OUTP
OUTN
AGND
25Ω
50Ω
25Ω
OUTP
OUTN
D0–D15
LVDS
DATA INPUTS
Figure 6. Differential Output Configuration
MAX5891
OUTPAV
DD3.3
AV
DD1.8
DV
DD3.3
DV
DD1.8
AV
CLK
OUTN
0.1μF
3.3V VOLTAGE SUPPLY
0.1μF
0.1μF 0.1μF
1.8V VOLTAGE SUPPLY
0.1μF
BYPASSING—DAC LEVEL
*FERRITE BEADS
D0–D15
LVDS
DATA INPUTS
*
**
**
Figure 7. Recommended Power-Supply Decoupling and
Bypassing Circuitry