Rainbow-electronics MAX5888 Manual de usuario descargar pdf (Pagina 16)

MAX5888

3.3V, 16-Bit, 500Msps High Dynamic

Performance DAC with Differential LVDS Inputs

16 ______________________________________________________________________________________

The MAX5888 is packaged in a 68-lead QFN-EP

package (package code: G6800-4), providing greater

design flexibility, increased thermal efficiency**, and

optimized AC performance of the DAC. The exposed

pad (EP) enables the user to implement grounding

techniques, which are necessary to ensure highest per-

formance operation. The EP must be soldered down

to AGND.

In this package, the data converter die is attached to

an EP lead frame with the back of this frame exposed at

the package bottom surface, facing the PC board side

of the package. This allows a solid attachment of the

package to the PC board with standard infrared (IR)

flow soldering techniques. A specially created land pat-

tern on the PC board, matching the size of the EP (6mm

✕ 6mm), ensures the proper attachment and grounding

of the DAC. Designing vias*** into the land area and

implementing large ground planes in the PC board

design allow for highest performance operation of the

DAC. An array of at least 4 ✕ 4 vias (≤0.3mm diameter

per via hole and 1.2mm pitch between via holes) is rec-

ommended for this 68-lead QFN-EP package.

Static Performance Parameter Definitions

Integral Nonlinearity (INL)

Integral nonlinearity is the deviation of the values on an

actual transfer function from either a best straight line fit

(closest approximation to the actual transfer curve) or a

line drawn between the end points of the transfer func-

tion, once offset and gain errors have been nullified. For

a DAC, the deviations are measured at every individual

step.

Differential Nonlinearity (DNL)

Differential nonlinearity is the difference between an

actual step height and the ideal value of 1 LSB. A DNL

error specification of less than 1 LSB guarantees no

missing codes and a monotonic transfer function.

FERRITE BEAD

1µF10µF47µF

ANALOG POWER-

SUPPLY SOURCE

FERRITE BEAD

1µF10µF47µF

DIGITAL POWER-

SUPPLY SOURCE

FERRITE BEAD

VCLK

1µF10µF47µF

CLOCK POWER-

SUPPLY SOURCE

AGND

MAX5888

B0–B15

0.1µF

DGND

0.1µF

VCLK

CLKGND

0.1µF

OUTP

OUTN

BYPASSING—DAC LEVEL BYPASSING—BOARD LEVEL

Figure 13. Recommended Power-Supply Decoupling and Bypassing Circuitry

**Thermal efficiency is not the key factor, since the MAX5888 features low-power operation. The exposed pad is the key element to

ensure a solid ground connection between the DAC and the PC board’s analog ground layer.

***Vias connect the land pattern to internal or external copper planes. It is important to connect as many vias as possible to the analog

ground plane to minimize inductance.

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