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LTC2355-12 Datasheet(PDF) 10 Page - Linear Technology |
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LTC2355-12 Datasheet(HTML) 10 Page - Linear Technology |
10 / 18 page LTC2355-12/LTC2355-14 0 2355fa DRIVING THE ANALOG INPUT ThedifferentialanaloginputsoftheLTC2355-12/LTC2355-14 may be driven differentially or as a single-ended input (i.e., the AIN– input is grounded). Both differential analog in- puts, AIN+ and AIN–, are sampled at the same instant. Any unwanted signal that is common to both inputs of each input pair will be reduced by the common mode rejection of the sample-and-hold circuit. The inputs draw only one small current spike while charging the sample-and-hold capacitors at the end of conversion. During conversion, the analog inputs draw only a small leakage current. If the source impedance of the driving circuit is low, then the LTC2355-12/LTC2355-14 inputs can be driven directly. As source impedance increases, so will acquisition time. For minimum acquisition time with high source impedance, a buffer amplifier must be used. The main requirement is that the amplifier driving the analog input(s) must settle after the small current spike before the next conversion starts (settling time must be 39ns for full throughput rate). Also keep in mind while choosing an input amplifier the amount of noise and harmonic distortion added by the amplifier. CHOOSING AN INPUT AMPLIFIER Choosing an input amplifier is easy if a few requirements are taken into consideration. First, to limit the magnitude of the voltage spike seen by the amplifier from charging the samplingcapacitor,chooseanamplifierthathasalowoutput impedance(<100Ω)attheclosed-loopbandwidthfrequency. For example, if an amplifier is used in a gain of 1 and has a unity-gainbandwidthof50MHz,thentheoutputimpedanceat 50MHz must be less than 100Ω. The second requirement is thattheclosed-loopbandwidthmustbegreaterthan40MHz to ensure adequate small-signal settling for full throughput rate. If slower op amps are used, more time for settling can be provided by increasing the time between conversions. The best choice for an op amp to drive the LTC2355-12/ LTC2355-14 will depend on the application. Generally, ap- plications fall into two categories: AC applications where dynamic specifications are most critical and time domain applications where DC accuracy and settling time are most critical. The following list is a summary of the op amps that are suitable for driving the LTC2355-12/LTC2355-14. (More applications inFormation detailed information is available in the Linear Technology Databooks and on the LinearView™ CD-ROM.) LTC1566-1: Low Noise 2.3MHz Continuous Time Low- Pass Filter. LT®1630: Dual 30MHz Rail-to-Rail Voltage FB Amplifier. 2.7V to ±15V supplies. Very high AVOL, 500µV offset and 520ns settling to 0.5LSB for a 4V swing. THD and noise are –93dB to 40kHz and below 1LSB to 320kHz (AV = 1, 2VP-P into 1kΩ, VS = 5V), making the part excellent for AC applications(to1/3Nyquist)whererail-to-railperformance is desired. Quad version is available as LT1631. LT1632: Dual 45MHz Rail-to-Rail Voltage FB Amplifier. 2.7V to ±15V supplies. Very high AVOL, 1.5mV offset and 400ns settling to 0.5LSB for a 4V swing. It is suitable for applications with a single 5V supply. THD and noise are –93dB to 40kHz and below 1LSB to 800kHz (AV = 1, 2VP-P into 1kΩ, VS = 5V), making the part excellent for ACapplicationswhererail-to-railperformanceisdesired. Quad version is available as LT1633. LT1813: Dual 100MHz 750V/µs 3mA Voltage Feedback Amplifier.5Vto±5Vsupplies.Distortionis–86dBto100kHz and –77dB to 1MHz with ±5V supplies (2VP-P into 500Ω). Excellent part for fast AC applications with ±5V supplies. LT1801: 80MHz GBWP, –75dBc at 500kHz, 2mA/Amplifier, 8.5nV/√Hz. LT1806/LT1807:325MHzGBWP,–80dBcDistortionat5MHz,Uni- ty-Gain Stable, R-R In and Out, 10mA/Amplifier, 3.5nV/√Hz. LT1810: 180MHz GBWP, –90dBc Distortion at 5MHz, Unity-Gain Stable, R-R In and Out, 15mA/Amplifier, 16nV/√Hz. LT1818/LT1819: 400MHz, 2500V/µs,9mA, Single/Dual Voltage Mode Operational Amplifier. LT6200: 165MHz GBWP, –85dBc Distortion at 1MHz, Unity-Gain Stable, R-R In and Out, 15mA/Amplifier, 0.95nV/√Hz. LT6203: 100MHz GBWP, –80dBc Distortion at 1MHz, Unity-Gain Stable, R-R In and Out, 3mA/Amplifier, 1.9nV/√Hz. LT6600-10: Amplifier/Filter Differential In/Out with 10MHz Cutoff. LinearView is a trademark of Linear Technology Corporation. |
Similar Part No. - LTC2355-12_15 |
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Similar Description - LTC2355-12_15 |
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