AD8698 데이터 시트보기 (PDF) - Analog Devices
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AD8698 Datasheet PDF : 20 Pages
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AD8698
APPLICATIONS
INPUT OVERVOLTAGE PROTECTION
The AD8698 has internal protective circuitry which allows
voltages at either input to exceed the supply voltage. However,
if voltages applied at either input exceed the supply voltage by
more than 2 V, it is recommended to use a resistor in series
with the inputs to limit the input current and prevent damaging
the device.
The value of the resistor can be calculated from the following
formula:
VIN −VS ≤5mA
RS + 500
DRIVING CAPACITIVE LOADS
The AD8698 is stable even when driving heavy capacitive
loads in any configuration. Although the AD8698 will safely
drive capacitive loads well over 10 nF, it is recommended to
use external compensation should the amplifier be subjected
to driving a load exceeding 50 nF. This is particularly
important in positive unity gain configurations, the worst
case for stability. Figure 49 shows the output of the AD8698
with a 68 nF load in response to a 400 mV signal at its
positive input; the overshoot is less than 25% without any
external compensation. Using a simple “snubber” network
reduces the overshoot to less than 10% as shown in
Figure 50.
VS = ±15V
CL = 68nF
AV = 1
VS = ±15V
CL = 68nF
RS = 30Ω
CS = 5nF
AV = 1
TIME (10µs/DIV)
Figure 50. Compensated Capacitive Load Drive with Snubber
The snubber network consists of a simple RC network
whose values are determined empirically.
V–
V+
+
– 400mV
RS
CL
CS
Figure 51. Snubber Network
Table 5 provides a few starting values for optimum
compensation.
Table 5. Compensation Values
CL (nF)
RS (Ω)
CS (nF)
47
20
7
68
30
5
100
50
3
The use of the snubber network does not recover the loss of
bandwidth incurred by the load capacitance. The AD8698
maintains a unity gain bandwidth of 1 MHz with load
capacitances of up to 1 nF.
TIME (10µs/DIV)
Figure 49. Heavy Capacitive Load Drive without Compensation
Rev. 0 | Page 14 of 20
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