MAX5890EGK+D【PDF 4/16 页】IC DAC 14BIT LVDS 600MSPS 68-QFN

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MAX5890

Grounding, Bypassing, and Power-Supply

Considerations

Grounding and power-supply decoupling strongly influ-

ence the MAX5890 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

MAX5890 dynamic performance.

Use a multilayer PCB with separate 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, refer-

ence input sense lines, common-mode inputs, and

clock inputs as practical. Use a symmetric design of

clock input and the analog output lines to minimize

2nd-order harmonic-distortion components, thus opti-

mizing the DAC’s dynamic performance. Keep digital

signal paths short and run lengths matched to avoid

propagation delay and data skew mismatches.

The MAX5890 requires five separate power-supply

inputs for analog (AVDD1.8 and AVDD3.3), digital

(DVDD1.8 and DVDD3.3), and clock (AVCLK) circuitry.

Decouple each AVDD3.3, AVDD1.8, AVCLK, DVDD3.3, and

DVDD1.8 input with a separate 0.1F 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 AVDD3.3,

AVCLK, and DVDD3.3 allow a 3.135V to 3.465V supply

voltage range. The analog and digital power-supply

inputs AVDD1.8 and DVDD1.8 allow a 1.71V to 1.89V

supply voltage range.

The MAX5890 is packaged in a 68-pin QFN-EP package

with exposed paddle, providing optimized DAC AC per-

formance. The exposed pad must be soldered to the

ground plane of the PCB. Thermal efficiency is not the

key factor, since the MAX5890 features low- power oper-

ation. The exposed pad ensures a solid ground connec-

tion 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

14-Bit, 600Msps, High-Dynamic-Performance

DAC with LVDS Inputs

______________________________________________________________________________________

MAX5890

OUTP

OUTN

AGND

OUTP

OUTN

D0–D13

LVDS

DATA INPUTS

Figure 6. Differential Output Configuration

MAX5890

OUTP

AVDD3.3

AVDD1.8

DVDD3.3

DVDD1.8

AVCLK

OUTN

0.1

3.3V VOLTAGE SUPPLY

0.1

1.8V VOLTAGE SUPPLY

0.1

BYPASSING—DAC LEVEL

*FERRITE BEADS

D0–D13

LVDS

DATA INPUTS

Figure 7. Recommended Power-Supply Decoupling and

Bypassing Circuitry

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