Satellite IF Switch

8

Detailed Description

The MAX12005 satellite IF switch features eight 75I

inputs with three selectable gain steps of 0, +6dB, and

+12dB. Each of the eight input amplifiers feeds into four

nine-to-one multiplexers with the switching controlled

by voltage/tone or DiSEqC signaling from up to four

receivers. The output of each multiplexer is then sent to

a satellite receiver through a 75I buffered output stage.

The satellite IF switch has four modes of operation. Two

modes are used to increase the number of IF inputs by

cascading two MAX12005 ICs together. The first IC is

set to master mode to enable the four cascade inputs.

The second IC is set to slave mode with its outputs

connected to the cascade inputs of the master IC.

The LNB mode sets up the IC to recognize LNB DiSEqC

signaling to control switching and ignore DiSEqC

signaling for multiswitch applications. The single mode

sets up the IC to recognize multiswitch DiSEqC signaling

to control switching and ignore LNB DiSEqC signaling.

For the LNB, single, and slave modes, the four cascade

inputs are disabled.

Input Gain Select

The voltage supplied to the GAIN_SELECT pin provides

the selection for one of three gain settings available at all

eight input stages, as follows:

GND = 0dB

The +6dB gain step voltage can be set through the

use of a simple supply voltage-divider. This gain select

feature is intended to compensate for input signal losses

due to the use of input RF signal splitters.

Chip Mode Select

The voltage supplied to the MODE_SELECT pin provides

the selection for one of four IC operational modes, as

follows:

GND = LNB Mode

The slave mode and master mode voltages can be set

through the use of simple supply voltage-dividers.

Switch Control

Voltage/tone signaling is the default switch control after

power-up or when a receiver is connected or recon-

nected with the die power on. After an individual decoder

receives a DiSEqC signal, that decoder switches from

voltage/one control to DiSEqC control until a new receiver

connection is made or when the IC has a power-on reset.

Layout Considerations

To minimize coupling between different sections of the

IC, a star power-supply routing configuration with a large

a bypass capacitor as close as possible to each sup-

ply pin. This arrangement provides local decoupling at

for a low-inductance ground connection. Do not share

the capacitor ground vias with any other branch. The

MAX12005 EV kit can be used as a starting point for

layout. For best performance, take into consideration

grounding and routing of RF, baseband, and power-

supply PCB proper line. Make connections from vias

to the ground plane as short as possible. On the high-

impedance ports, keep traces short to minimize shunt

capacitance. EV kit schematic and Gerber files can be

found at www.maxim-ic.com.

SPI is a trademark of Motorola, Inc.