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ISL43410IR-T Fiches technique(PDF) 9 Page - Intersil Corporation |
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ISL43410IR-T Fiches technique(HTML) 9 Page - Intersil Corporation |
9 / 13 page 9 FN6044.4 May 12, 2008 . Power-Supply Considerations The ISL43410 construction is typical of most CMOS analog switches, except that they have only two supply pins: V+ and GND. V+ and GND drive the internal CMOS switches and set their analog voltage limits. Unlike switches with a 13V maximum supply voltage, the ISL43410’s 15V maximum supply voltage provides plenty of room for the 10% tolerance of 12V supplies, as well as room for overshoot and noise spikes. The minimum recommended supply voltage is 2.0V. 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 beginning on page 3 and “Typical Performance Curves” on page 10 for details. V+ and GND also power the internal logic and level shifters. The level shifters convert the input logic levels to switched V+ and GND signals to drive the analog switch gate terminals. This device cannot be operated with bipolar supplies because the input switching point becomes negative in this configuration. Logic-Level Thresholds The ISL43410 is TTL compatible (0.8V and 2.4V) over a supply range of 3V to 11V (see Figure 11). At 12V, the VIH level is about 2.5V. This is still below the TTL guaranteed high output minimum level of 2.8V, but noise margin is reduced. For best results with a 12V supply, use a logic family that 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 (see Figure 12). Driving the digital input signals from GND to V+ with a fast transition time minimizes power dissipation. The ISL43410 has been designed to minimize the supply current whenever the digital input voltage is not driven to the supply rails (0V to V+). For example, driving the device with 3V logic (0V to 3V) while operating with a 5V supply, the device draws only 10µA of current (see Figure 12 for VIN = 3V). Similar devices of competitors can draw 8x this amount of current. High-Frequency Performance In 50 Ω systems, signal response is reasonably flat even past 100MHz (see Figure 17). Figure 17 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 feed through from a switch’s input to its output. OFF-Isolation is the resistance to this feed through, while crosstalk indicates the amount of feed through from one switch to another. Figure 18 details the high OFF-Isolation and crosstalk rejection provided by this family. At 10MHz, OFF-Isolation is about 55dB in 50 Ω 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. Leakage Considerations Reverse ESD protection diodes are internally connected between each analog-signal pin and both V+ and GND. One of these diodes conducts if any analog signal exceeds V+ or GND. Virtually all the analog leakage current comes from the ESD diodes to V+ or GND. Although the ESD diodes on a given signal pin are identical and therefore fairly well balanced, they are reverse biased differently. Each is biased by either V+ or GND and the analog signal. This means their leakages will vary as the signal varies. The difference in the two diode leakages to the V+ and GND pins constitutes the analog-signal-path leakage current. All analog leakage current flows between each pin and one of the supply terminals, not to the other switch terminal. This is why both sides of a given switch can show leakage currents of the same or opposite polarity. There is no connection between the analog signal paths and V+ or GND. GND VCOM VNO OR NC OPTIONAL PROTECTION V+ IN DIODE OPTIONAL PROTECTION DIODE OPTIONAL PROTECTION RESISTOR FOR LOGIC INPUTS 1k Ω ADD 1k Ω FIGURE 8. OVERVOLTAGE PROTECTION ISL43410 |
Numéro de pièce similaire - ISL43410IR-T |
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Description similaire - ISL43410IR-T |
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