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LT1492 数据表(PDF) 12 Page - Linear Technology |
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LT1492 数据表(HTML) 12 Page - Linear Technology |
12 / 16 page 12 LT1492/LT1493 Feedback Components Because the input currents of the LT1492/LT1493 are less than 100nA, it is possible to use high value feedback resistors to set the gain. However, care must be taken to insure that the pole that is formed by the feedback resis- tors and the input capacitance does not degrade the stability of the amplifier. For example, if a single supply, noninverting gain of 2 is set with two 62k resistors, the LT1492/LT1493 will probably oscillate. This is because the amplifier goes open-loop at 1MHz (6dB of gain) and has 50 ° of phase margin. The feedback resistors and the 10pF input capacitance generate a pole at 500kHz that introduces 63 ° of phase shift at 1MHz! The solution is simple, lower the values of the resistors or add a feedback capacitor of 10pF or more. Capacitive Loading The LT1492/LT1493 are optimized for low voltage, single supply operation. The Maximum Capacitive Load vs Load Current typical performance curve shows the circuit per- formance without any load resistance. When the output is sinking current or driving heavy loads with high supplies, capacitive load handling is degraded. APPLICATIONS INFORMATION Comparator Applications Sometimes it is desirable to use an op amp as a compara- tor. When operating the LT1492/LT1493 on a single 3.3V or 5V supply, the output interfaces directly with most TTL and CMOS logic. The response time of the LT1492/LT1493 is a strong function of the amount of input overdrive as shown in the following photos. These amplifiers are unity-gain stable op amps and not fast comparators, therefore, the logic being driven may oscillate due to the long transition time. The output can be speeded up by adding 20mV or more of hysteresis (positive feedback), but the offset is then a function of the input direction. Maximum Capacitive Load vs Load Current Comparator Response (+) 20mV, 10mV, 5mV, 2mV Overdrives 4 2 0 0 100 20 µs/DIV VS = 5V RL = ∞ 1492/93 AI02 Comparator Response (–) 20mV, 10mV, 5mV, 2mV Overdrives 20 µs/DIV VS = 5V RL = ∞ 1492/93 AI02 0 4 2 0 100 LOAD CURRENT (mA) 0.1 10 100 1000 10000 1 10 100 1492/93 AI01 SOURCING SINKING VS = ±2.5V VS = ±2.5V VS = ±15V VS = ±15V |
类似零件编号 - LT1492 |
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类似说明 - LT1492 |
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