Datasheet LT1497 (Analog Devices) - 10

LT1497
U U W U APPLICATIONS INFORMATION
the normally active emitter of Q2 will turn off as the entire configurations there is much less slew rate enhancement current available from the current source is used to slew because the input only moves 2V, barely enough to turn on the base of Q3. The base of Q4 is driven by Q1 without slew the input clamps. In inverting configurations as shown in limitation. When the differential input voltage exceeds two Figure 4 the noninverting input does not move so there is diode drops (about 1.4V) the extra clamp emitter on Q1 no input slew rate limitation. Slew overshoot is due to turns on and drives the base of Q3 directly. Once the base capacitance on the inverting input and can be reduced with of Q3 has been driven within 1.4V of its final value, the a larger feedback resistor. clamp emitter of Q1 turns off and the node must finish The output slew rate is set by the value of the feedback slewing using the current source. resistors and the internal capacitance. Larger feedback This effect can be seen in Figure 2 which shows the large resistors will reduce the slew rate as will lower supply signal behavior in a gain of 1 on ±15V supplies. The voltages, similar to the way the bandwidth is reduced. clamping action enhances the slew rate beyond the input The larger feedback resistors will also cut back on slew limitation, but always leads to slew overshoot after the overshoot. clamps turn off. Figure 3 shows that for higher gain 1497 F02 A 1497 F03 1497 F04 V = 1 RF = 560Ω AV = 10 RF = 560Ω RG = 62Ω AV = –1 RF = RG = 560Ω VS = ±15V RL = 100Ω VS = ±15V RL = 100Ω VS = ±15V RL = 100Ω
Figure 2. Large-Signal Response Figure 3. Large-Signal Response Figure 4. Large-Signal Response W W SI PLIFIED SCHE ATIC One Amplifier
V+ Q6 Q5 Q7 Q13 Q3 Q8 Q2 +IN – IN VOUT Q1 Q9 Q4 Q14 Q11 Q10 Q12 V– 1497 SS 10