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ISL8484 Datasheet(PDF) 8 Page - Intersil Corporation |
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ISL8484 Datasheet(HTML) 8 Page - Intersil Corporation |
8 / 13 page 8 FN6128.2 September 13, 2006 overvoltage protection for all pins (see Figure 8). These additional diodes limit the analog signal from 1V below V+ to 1V above GND. The low leakage current performance is unaffected by this approach, but the switch signal range is reduced and the resistance may increase, especially at low supply voltages. Power-Supply Considerations The ISL8484 construction is typical of most single supply CMOS analog switches, in that they have two supply pins: V+ and GND. V+ and GND drive the internal CMOS switches and set their analog voltage limits. Unlike switches with a 4V maximum supply voltage, the ISL8484 4.7V maximum supply voltage provides plenty of room for the 10% tolerance of 4.3V supplies, as well as room for overshoot and noise spikes. The minimum recommended supply voltage is 1.65V. It is important to note that the input signal range, switching times, and on-resistance degrade at lower supply voltages. Refer to the “Electrical Specifications” tables, beginning on page 3, and “Typical Performance Curves”, beginning on page 9, for details. V+ and GND also power the internal logic and level shiftiers. The level shiftiers convert the input logic levels to switched V+ and GND signals to drive the analog switch gate terminals. This family of switches cannot be operated with bipolar supplies, because the input switching point becomes negative in this configuration. Logic-Level Thresholds This switch family is 1.8V CMOS compatible (0.5V and 1.4V) over a supply range of 2.7V to 4.5V (see Figure 16). At 2.7V the VIL level is about 0.53V. This is still above the 1.8V CMOS guaranteed low output maximum level of 0.5V, but noise margin is reduced. 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. The ISL8484 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 2.85V logic (0V to 2.85V) while operating with a 4.2V supply the device draws only 8µA of current (see Figure 14 for VIN = 2.85V). High-Frequency Performance In 50 Ω systems, the signal response is reasonably flat even past 30MHz with a -3dB bandwidth of 120MHz (see Figure 19). 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 20 details the high Off Isolation and Crosstalk rejection provided by this part. At 100kHz, Off Isolation is about 68dB 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. FIGURE 8. OVERVOLTAGE PROTECTION GND VCOM VNO OR NC OPTIONAL PROTECTION V+ INX DIODE OPTIONAL PROTECTION DIODE OPTIONAL PROTECTION RESISTOR ISL8484 |
Similar Part No. - ISL8484_06 |
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Similar Description - ISL8484_06 |
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