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ADG3247BRU Arkusz danych(PDF) 10 Page - Analog Devices |
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ADG3247BRU Arkusz danych(HTML) 10 Page - Analog Devices |
10 / 12 page REV. 0 –10– ADG3247 VIN 1.8V VOUT 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 ADG3247 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 ADG3247 is suitable for hot swap and hot plug applications. The output signal of the ADG3247 is limited to a voltage that is below the VCC supply, as shown in Figures 6, 8, and 10. There- 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. ADG3247 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, BEx should be tied to VCC through a pull-up resistor; the minimum value of the resistor is determined by the current- sinking capability of the driver. PACKAGE AND PINOUT The ADG3247 is packaged in both a small 38-lead TSSOP or a tiny 40-lead LFCSP package. The area of the TSSOP option is 62.7 mm 2, while the area of the LFCSP option is 36 mm2. This leads to a 43% savings in board space when using the LFCSP package compared with the TSSOP package. This makes the LFCSP option an excellent choice for space-constrained applications. The ADG3247 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. |
Podobny numer części - ADG3247BRU |
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Podobny opis - ADG3247BRU |
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