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MAX4522CPE Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX4522CPE Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 15 page Applications Information Power-Supply Considerations Overview The MAX4521/MAX4522/MAX4523 construction is typi- cal of most CMOS analog switches. They have three supply pins: V+, V-, and GND. V+ and V- are used to drive the internal CMOS switches, and they set the lim- its of the analog voltage on any switch. Reverse ESD- protection diodes are internally connected between each analog-signal pin and both V+ and V-. If any ana- log signal exceeds V+ or V-, one of these diodes con- ducts. During normal operation these reverse-biased ESD diodes leak, forming the only current drawn from V+ or V-. Virtually all the analog leakage current is through the ESD diodes. Although the ESD diodes on a given sig- nal pin are identical and therefore fairly well balanced, they are reverse biased differently. Each is biased by either V+ or V- and the analog signal. This means their leakages vary as the signal varies. The difference in the two diode leakages from the signal path to the V+ and V- pins constitutes the analog-signal-path leakage cur- rent. All analog leakage current flows to the supply ter- minals, not to the other switch terminal. This explains how 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 GND. The analog-signal paths consist of an N-channel and P-channel MOSFET with their sources and drains paralleled, and their gates driven out of phase to V+ and V- by the logic-level translators. V+ and GND power the internal logic and logic-level translators, and set the input logic thresholds. The logic-level translators convert the logic levels to switched V+ and V- signals to drive the gates of the analog switches. This drive signal is the only connec- tion between the logic supplies and the analog sup- plies. V+ and V- have ESD-protection diodes to GND. The logic-level inputs and output have ESD protection to V+ and to GND. Increasing V- has no effect on the logic-level thresh- olds, but it does increase the drive to the P-channel switches, reducing their on-resistance. V- also sets the negative limit of the analog-signal voltage. The logic-level thresholds are CMOS/TTL compatible when V+ = +5V. The threshold increases slightly as V+ is raised, and when V+ reaches +12V, the level thresh- old is about 3.1V. This is above the TTL output high- level minimum of 2.8V, but still compatible with CMOS outputs. Bipolar Supplies The MAX4521/MAX4522/MAX4523 operate with bipolar supplies between ±2V and ±6V. The V+ and V- sup- plies need not be symmetrical, but their sum cannot exceed the absolute maximum rating of 13.0V. Do not connect the MAX4521/MAX4522/MAX4523 V+ to +3V, and then connect the logic-level-input pins to TTL logic-level signals. TTL logic-level outputs in excess of the absolute maximum ratings can damage the part and/or external circuits. Caution: The absolute maximum V+ to V- differential voltage is 13.0V. Typical ±6V or 12V supplies with ±10% tolerances can be as high as 13.2V. This voltage can damage the MAX4521/MAX4522/MAX4523. Even ±5% tolerance supplies may have overshoot or noise spikes that exceed 13.0V. Single Supply The MAX4521/MAX4522/MAX4523 operate from a single supply between +2V and +12V when V- is con- nected to GND. All of the bipolar precautions must be observed. High-Frequency Performance In 50 Ω systems, signal response is reasonably flat up to 50MHz (see Typical Operating Characteristics). Above 20MHz, the on-response has several minor peaks that are highly layout dependent. The problem with high-frequency operation is not turning the switch on, but turning it off. The off-state switch acts like a capacitor and passes higher frequencies with less attenuation. At 10MHz, off-isolation is about -52dB in 50 Ω systems, becoming worse (approximately 20dB per decade) as frequency increases. Higher circuit impedances also make off-isolation worse. Adjacent channel attenuation is about 3dB above that of a bare IC socket, and is due entirely to capacitive coupling. Quad, Low-Voltage, SPST Analog Switches 8 _______________________________________________________________________________________ |
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