PRELIMINARY TECHNICAL DATA

REV. Pr

C

–10–

ADG3246

1.8V

0V

3.3V

SWITCH

INPUT

3.3V SUPPLY

SEL = 0V

Figure 10. 3.3 V to 1.8 V Voltage Translation,

SEL = 0 V

Bus Isolation

A common requirement of bus architectures is low capacitance

loading of the bus. Such systems require bus bridge devices that

extend the number of loads on the bus without exceeding the

specifications. Because the ADG3246 is designed specifically for

applications that do not need drive yet require simple logic func-

tions, it solves this requirement. The device isolates access to the

bus, thus minimizing capacitance loading.

Bus/

Backplane

Load A

Load C

Load B

Load D

Bus Switch

Location

Figure 11. Location of Bus Switched in a Bus

Isolation Application

Hot Plug and Hot Swap Isolation

The ADG3246 is suitable for hot swap and hot plug applications.

The output signal of the ADG3246 is limited to a voltage that is

fore the switch acts like a buffer to take the impact from hot

insertion, protecting vital and expensive chipsets from damage.

In hot-plug applications, the system cannot be shutdown when

new hardware is being added. To overcome this, a bus switch

can be positioned on the backplane between the bus devices and

the hot plug connectors. The bus switch is turned off during hot

plug. Figure 12 shows a typical example of this type of application.

PLUG-IN

CARD (1)

CARD I/O

CARD I/O

RAM

CPU

PLUG-IN

CARD (2)

Figure 12. ADG3246 in a Hot Plug Application

There are many systems that require the ability to handle hot

swapping, such as docking stations, PCI boards for servers, and

line cards for telecommunications switches. If the bus can be

isolated prior to insertion or removal, then there is more control

over the hot swap event. This isolation can be achieved using a

bus switch. The bus switches are positioned on the hot swap card

between the connector and the devices. During hot swap, the

ground pin of the hot swap card must connect to the ground pin

of the back plane before any other signal or power pins.

Analog Switching

Bus switches can be used in many analog switching applications;

for example, video graphics. Bus switches can have lower on

resistance, smaller ON and OFF channel capacitance and thus

improved frequency performance than their analog counterparts.

The bus switch channel itself consisting solely of an NMOS

switch limits the operating voltage (see TPC 1 for a typical plot),

but in many cases this does not present an issue.

High Impedance During Power-Up/Power-Down

To ensure the high impedance state during power-up or power-

down,

BE should be tied to V

minimum value of the resistor is determined by the current-

sinking capability of the driver.

PACKAGE AND PINOUT

The ADG3246 is packaged in both a small 24-lead TSSOP or a

tiny 24-lead LFCSP package. The area of the TSSOP option is

49.375 mm

leads to a 67% savings in board space when using the LFCSP pack-

age compared with the TSSOP package. This makes the LFCSP

option an excellent choice for space-constrained applications.

The ADG3246 in the TSSOP package offers a flowthrough

pinout. The term flowthrough signifies that all the inputs are on

opposite sides from the outputs. A flowthrough pinout simplifies

the PCB layout.