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ISL43141IR Fiches technique(PDF) 10 Page - Intersil Corporation |
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ISL43141IR Fiches technique(HTML) 10 Page - Intersil Corporation |
10 / 16 page 10 Detailed Description The ISL43140–ISL43142 quad analog switches offer precise switching capability from a bipolar ±2V to ±6V or a single 2V to 12V supply with low on-resistance (50 Ω) and high speed switching (tON = 40ns, tOFF = 15ns). The devices are especially well suited to portable battery powered equipment thanks to the low operating supply voltage (2V), low power consumption (1 µW), low leakage currents (1nA max), and the tiny QFN packaging. High frequency applications also benefit from the wide bandwidth, and the very high off isolation and crosstalk rejection. Supply Sequencing And Overvoltage Protection With any CMOS device, proper power supply sequencing is required to protect the device from excessive input currents which might permanently damage the IC. All I/O pins contain ESD protection diodes from the pin to V+ and to V- (see Figure 8). To prevent forward biasing these diodes, V+ and V- must be applied before any input signals, and input signal voltages must remain between V+ and V-. If these conditions cannot be guaranteed, then one of the following two protection methods should be employed. Logic inputs can easily be protected by adding a 1k Ω resistor in series with the input (see Figure 8). The resistor limits the input current below the threshold that produces permanent damage, and the sub-microamp input current produces an insignificant voltage drop during normal operation. Adding a series resistor to the switch input defeats the purpose of using a low RON switch, so two small signal diodes can be added in series with the supply pins to provide overvoltage protection for all pins (see Figure 8). These additional diodes limit the analog signal from 1V below V+ to 1V above V-. The low leakage current performance is unaffected by this approach, but the switch resistance may increase, especially at low supply voltages. Power-Supply Considerations The ISL4314X construction is typical of most CMOS analog switches, in that they have three supply pins: V+, V-, and GND. V+ and V- drive the internal CMOS switches and set their analog voltage limits, so there are no connections between the analog signal path and GND. Unlike switches with a 13V maximum supply voltage, the ISL4314X 15V maximum supply voltage provides plenty of room for the 10% tolerance of 12V supplies (±6V or 12V single supply), as well as room for overshoot and noise spikes. This family of switches performs equally well when operated with bipolar or single voltage supplies. The addition of the GND pin allows for asymmetrical bipolar supplies (e.g. +5V and -3V). The minimum recommended supply voltage is 2V or ±2V. It is important to note that the input signal range, switching times, and on-resistance degrade at lower supply voltages. Refer to the electrical specification tables and Typical Performance Curves for details. V+ and GND power the internal logic (thus setting the digital switching point) and level shifters. The level shifters convert the logic levels to switched V+ and V- signals to drive the analog switch gate terminals, so switch parameters - especially RON - are strongly influenced by V-. Logic-Level Thresholds V+ and GND power the internal logic stages, so V- has no affect on logic thresholds. This switch family is TTL compatible (0.8V and 2.4V) over a V+ supply range of 2.5V to 10V (see Figure 17). At 12V the VIH level is about 2.7V, so for best results use a logic family the provides a VOH greater than 3V. The digital input stages draw supply current whenever the digital input voltage is not at one of the supply rails. Driving the digital input signals from GND to V+ with a fast transition time minimizes power dissipation. High-Frequency Performance In 5 0Ω systems, signal response is reasonably flat even past 100MHz (see Figure 18). Figure 18 also illustrates that the frequency response is very consistent over a wide V+ range, and for varying analog signal levels. An off switch acts like a capacitor and passes higher frequencies with less attenuation, resulting in signal feedthrough from a switch’s input to its output. Off Isolation is the resistance to this feedthrough, while Crosstalk indicates the amount of feedthrough from one switch to another. Figure 19 details the high Off Isolation and Crosstalk rejection provided by this family. At 10MHz, off isolation is about 50dB in 5 0Ω systems, decreasing approximately 20dB per decade as frequency increases. Higher load impedances decrease Off Isolation and Crosstalk rejection due to the voltage divider action of the switch OFF impedance and the load impedance. FIGURE 8. OVERVOLTAGE PROTECTION V- VCOM VNO or NC OPTIONAL PROTECTION V+ INX DIODE OPTIONAL PROTECTION DIODE OPTIONAL PROTECTION RESISTOR ISL43140, ISL43141, ISL43142 |
Numéro de pièce similaire - ISL43141IR |
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Description similaire - ISL43141IR |
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