LT6275 データシートの表示（PDF） - Analog Devices
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LT6275 Datasheet PDF : 20 Pages
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LT6274/LT6275
TYPICAL APPLICATIONS
Noninverting Amplifier Slew Rate and Step Response
RG
RF
Figure 1 shows a noninverting amplifier with closed-loop
gain of 11V/V. The closed-loop bandwidth of this ampli-
fier is approximately GBW/11 (GBW = Gain-Bandwidth
Product). For a step input, the output follows an expo-
nential curve:
VOUT
= VINITIAL + AV
• VINPUTSTEP
•
⎛
⎜⎜⎜1–
e
–⎛⎜
⎝
t
τ
⎞
⎟
⎠
⎞
⎟
⎟⎟
(1)
⎝
⎠
where τ = time constant associated with the closed-loop
bandwidth.
The maximum slew rate occurs in the beginning of the
output response:
VOUTSRMAX
=
A
V
•
VINPUSTEP
•
1
τ
(2)
Keep in mind that the closed-loop bandwidth and the
closed-loop gain are related (τ = τo AV), so Equation (2)
is simplified to:
VOUTSRMAX
=
VINPUTSTEP
•
1
τo
(3)
200
2k
+15V
1/2 LT6275
VIN
–15V
VOUT
6275 TA06
Figure 1. LT6275 Configured in a Noninverting Gain of AV = +11V/V
15
12 AV = +11
9
6
3
0
–3
–6
–9
–12
–15
50ns/DIV
6275 TA07
Figure 2. Noninverting Amplifier Step Response (AV = +11V/V)
where τo = time constant associated with the LT6274/ capability ensures that the output response is never slew
LT6275 GBW.
rate limited despite the very high excursion.
Interestingly, Equation (3) reveals that the maximum slew
rate is nominally related only to the input step size and the
op amp’s inherent GBW. Closing the loop to implement
AV > 1 gain configurations slows down the response, but
increases the excursion. The resulting maximum slew rate
remains the same.
The LT6274/LT6275 feature ample slew rate capability
with low power consumption. Because the input stage
architecture allows high slew rate with low input stage
quiescent currents, the overall power consumption when
amplifying pulses is very low; additional power is only
drawn from the supplies during the highest slew rate
moments of the exponential response.
Since GBW of the LT6274/LT6275 is 40MHz, Equation (3)
suggests that the maximum slew rate in a step response
whose output swings 25V (implying VINPUTSTEP = 25/11
= 2.27V) is 571V/µs. The LT6274/LT6275 high slew
Figure 2 shows the output response to varying input step
amplitudes. Note that none of the exponential responses
is limited by the initial slew rate (which increases with
increasing amplitude).
As a particular example, with AV = +11V/V, 15V output
excursion, and 40 MHz GBW, Equation (3) predicts a
maximum slew rate of 343V/μs. Measurement on the cor-
responding curve in Figure 2 shows 390V/μs, which is in
good agreement with the prediction. As another example,
with an 18.5V output excursion, the predicted maximum
slew rate is 423V/μs; measurement shows 460V/μs.
As the peak to peak voltage of the input step changes, the
maximum initial slew rate changes. The 63% rise time
of the closed loop response, however, does not change
(as seen in Figure 2), because the closed loop bandwidth
stays constant for all input amplitudes.
6275fa
14
For more information www.linear.com/LT6275
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