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ISL59442IBZ Datasheet(PDF) 9 Page - Intersil Corporation |
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ISL59442IBZ Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 11 page 9 FN7452.4 January 5, 2007 Application Information General The ISL59442 is a 4:1 mux that is ideal as a matrix element in high performance switchers and routers. The ISL59442 is optimized to drive a 2pF in parallel with a 500 Ω load. The capacitance can be split between the PCB capacitance an and external load capacitance. Their low input capacitance and high input resistance provide excellent 50 Ω or 75Ω terminations. Capacitance at the Output The output amplifier is optimized for capacitance to ground (CL) directly on the output pin. Increased capacitance causes higher peaking with an increase in bandwidth. The optimum range for most applications is ~1.0pF to ~6pF. The optimum value can be achieved through a combination of PC board trace capacitance (CT) and an external capacitor (COUT). A good method to maintain control over the output pin capacitance is to minimize the trace length (CT) to the next component, and include a discrete surface mount capacitor (COUT) directly at the output pin. For large signal applications where overshoot is important the circuit in Figure 24B should be used. The series resistor (RS) and capacitor (CL) form a low pass network that limits system bandwidth and reduces overshoot. The component values shown result in a typical pulse response shown in Figure 20. Ground Connections For the best isolation and crosstalk rejection, the GND pin and NIC pins must connect to the GND plane. The NIC pins are placed on both sides of the input pins. These pins are not internally connected to the die. It is recommended this pin be tied to ground to minimize crosstalk. Control Signals S0, S1, HIZ - These pins are, TTL/CMOS compatible control inputs. The S0, S1 pins select which one of the inputs connect to the output. The HIZ pin is used to three-state the output amplifiers. For control signal rise and fall times less than 10nsec the use of termination resistors close to the part will minimize transients coupled to the output. Power-Up Considerations The ESD protection circuits use internal diodes from all pins the V+ and V- supplies. In addition, a dV/dT- triggered clamp is connected between the V+ and V- pins, as shown in the Equivalent Circuits 1 through 4 section of the Pin Description table. The dV/dT triggered clamp imposes a maximum supply turn-on slew rate of 1V/µs. Damaging currents can flow for power supply rates-of-rise in excess of 1V/µs, such as during hot plugging. Under these conditions, additional methods should be employed to ensure the rate of rise is not exceeded. Consideration must be given to the order in which power is applied to the V+ and V- pins, as well as analog and logic input pins. Schottky diodes (Motorola MBR0550T or equivalent) connected from V+ to ground and V- to ground (Figure 25) will shunt damaging currents away from the internal V+ and V- ESD diodes in the event that the V+ supply is applied to the device before the V- supply. If positive voltages are applied to the logic or analog video input pins before V+ is applied, current will flow through the internal ESD diodes to the V+ pin. The presence of large decoupling capacitors and the loading effect of other circuits connected to V+, can result in damaging currents through the ESD diodes and other active circuits within the device. Therefore, adequate current limiting on the digital and analog inputs is needed to prevent damage during the time the voltages on these inputs are more positive than V+. HIZ State An internal pull-down resistor connected to the HIZ pin ensures the device will be active with no connection to the HIZ pin. The HIZ state is established within approximately 30ns by placing a logic high (>2V) on the HIZ pin. If the HIZ state is selected, the output is a high impedance 1.4M Ω. Use this state to control the logic when more than one mux shares a common output. In the HIZ state the output is three-stated, and maintains its high Z even in the presence of high slew rates. The supply current during this state is basically the same as the active state. Limiting the Output Current No output short circuit current limit exists on these parts. All applications need to limit the output current to less than 50mA. Adequate thermal heat sinking of the parts is also required. V+ V+ V- V- V+ V- V+ V- LOGIC CONTROL GND IN0 IN1 S0 OUT EXTERNAL CIRCUITS SCHOTTKY PROTECTION V+ V- POWER GND SIGNAL LOGIC V+ SUPPLY V- SUPPLY DE-COUPLING CAPS FIGURE 25. SCHOTTKY PROTECTION CIRCUIT ISL59442 |
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