LT1207 OUUWUAPPLICATIS I FOR ATIO The amplifier’s supply current will be approximately 40 and for higher gains in the noninverting mode, the signal times the current in the Shutdown pin. The voltage across amplitude on the input pins is small and the overall slew the resistor in this condition is V+ – 3V rate is that of the output stage. The input stage slew rate BE. For example, a 60k resistor will set the amplifier’s supply current to 10mA is related to the quiescent current and will be reduced as with V the supply current is reduced. The output slew rate is set S = ±15V. by the value of the feedback resistors and the internal The photos (Figures 4a and 4b) show the effect of reducing capacitance. Larger feedback resistors will reduce the the quiescent supply current on the large-signal response. slew rate as will lower supply voltages, similar to the way The quiescent current can be reduced to 5mA in the the bandwidth is reduced. The photos (Figures 5a, 5b and inverting configuration without much change in response. 5c) show the large-signal response of the LT1207 or In noninverting mode, however, the slew rate is reduced various gain configurations. The slew rate varies from as the quiescent current is reduced. 860V/µs for a gain of 1, to 1400V/µs for a gain of – 1. When the LT1207 is used to drive capacitive loads, the available output current can limit the overall slew rate. In the fastest configuration, the LT1207 is capable of a slew rate of over 1V/ns. The current required to slew a capacitor LT1207 • F04a RF = 750Ω IQ = 5mA, 10mA, 20mA RL = 50Ω VS = ±15V Figure 4a. Large-Signal Response vs IQ, AV = –1 LT1207 • F05a RF = 825Ω VS = ±15V RL = 50Ω Figure 5a. Large-Signal Response, AV = 1 LT1207 • F04b RF = 750Ω IQ = 5mA, 10mA, 20mA RL = 50Ω VS = ±15V Figure 4b. Large-Signal Response vs IQ, AV = 2Slew Rate Unlike a traditional op amp, the slew rate of a current feedback amplifier is not independent of the amplifier gain LT1207 • F05b RF = RG = 750Ω VS = ±15V R configuration. There are slew rate limitations in both the L = 50Ω input stage and the output stage. In the inverting mode, Figure 5b. Large-Signal Response, AV = –1 10