MAX19794ETX+【PDF 22/25 页】ATTENUATR 46DB 50OHM 4GHZ 36TQFN

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MAX19794

10MHz to 500MHz Dual Analog Voltage Variable

Attenuator with On-Chip 10-Bit SPI-Controlled DAC

Layout Considerations

A properly designed PCB is an essential part of any

RF/microwave circuit. Keep RF signal lines as short as

possible to reduce losses, radiation, and inductance. For

best performance, route the ground-pin traces directly

to the exposed pad underneath the package. This pad

must be connected to the ground plane of the board by

using multiple vias under the device to provide the best

RF and thermal conduction path. Solder the exposed

pad on the bottom of the device package to a PCB.

RF Ground Return Capacitors

The device requires RF ground return capacitors C10

and C11. The value of these capacitors optimize the

dynamic range and frequency flatness for the RF band of

interest. Some recommended values are shown in Table

7 along with the resulting performance in the Typical

Operating Characteristics section.

Figure 2. SPI Timing Diagram

Figure 3. UP DWN Control Diagram (Mode = 1)

SPI Interface Programming

Table 7. Typical Application Circuit Component Values

*Add 2 additional 10I resistors between the V

pins leading to C5 and C6 unless a V

power plane is used.

DESIGNATION

QTY

DESCRIPTION

C1, C2, C4

0.01FF Q5% 50V X7R ceramic capacitors (0402).

Not installed for two attenuators in cascade

C5C9

1000pF Q5% 50V COG ceramic capacitors (0402)

C10, C11

10MHz to 200MHz

0.01FF Q10% 50V X7R ceramic capacitors

(0402)

250MHz to 500MHz

100pF Q5% 50V COG ceramic capacitors

(0402)

C12

120pF Q5% 50V COG CER CAP (0402).Provides some external noise filtering along with R3.

C13

Not installed. A 4.7pF capacitor could be used to reduce any potential rise time glitching when

the comparator changes state.

R1*, R2*

10I Q5% resistor (0402)

200I Q5% resistor (0402). This resistor is used to provide some lowpass noise filtering when

used with C12. The value of R3 slows down the response time. R3 also provides protection for

the device in case V

CTRL

is applied without V

present.

MAX19794

R/W A1 A0

D9, D8...D0 TO REGISTER 0, 1, 2, 3

CLK

D9, D8...D0 FROM REGISTER 0, 1, 2, 3

OUT

HIGH-Z

EWS

DWN

NO DAC

CODE CHANGE

DAC CODE

INCREASED

BY STEP UP

DAC CODE

DECREASED

BY STEP DOWN

DAC CODE

RESET TO

ALL 0's

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