參數資料
型號: AD744AQ
廠商: Analog Devices Inc
文件頁數: 11/12頁
文件大小: 0K
描述: IC OPAMP BIFET 13MHZ PREC 8CDIP
標準包裝: 48
放大器類型: J-FET
電路數: 1
轉換速率: 75 V/µs
-3db帶寬: 13MHz
電流 - 輸入偏壓: 30pA
電壓 - 輸入偏移: 300µV
電流 - 電源: 3.5mA
電流 - 輸出 / 通道: 25mA
電壓 - 電源,單路/雙路(±): ±4.5 V ~ 18 V
工作溫度: -40°C ~ 85°C
安裝類型: 通孔
封裝/外殼: 8-CDIP(0.300",7.62mm)
供應商設備封裝: 8-CERDIP
包裝: 管件
REV. C
AD744
–8–
EXTERNAL FREQUENCY COMPENSATION
Even though the AD744 is useable without compensation in
most applications, it may be externally compensated for even
more flexibility. This is accomplished by connecting a capacitor
between Pins 5 and 8. Figure 28, a simplified schematic of the
AD744, shows where this capacitor is connected. This feature is
useful because it allows the AD744 to be used as a unity gain
voltage follower. It also enables the amplifier to drive capacitive
loads up to 2000 pF and greater.
5pF
+IN
300
–IN
NULL /
COMPENSATION
NULL /
DECOMPENSATION
300
COMPENSATION
2mA
400 A
+VS
OUTPUT
–VS
1k
8k
Figure 28. AD744 Simplified Schematic
The slew rate and gain bandwidth product of the AD744 are in-
versely proportional to the value of the compensation capacitor,
CCOMP. Therefore, when trying to maximize the speed of the
amplifier, the value of CCOMP should be minimized. CCOMP can
also be used to slow the amplifier to a point where the slew rate
is perfectly symmetrical and well controlled. Figure 29 sum-
marizes the effect of external compensation on slew rate and
bandwidth.
CCOMP – pF
2
0
GAIN
BANDWIDTH
MHz
20
0.02
0.2
10
100
1000
10
SLEW
RATE
V/
s
100
0.1
1.0
Figure 29. Gain Bandwidth and Slew Rate vs. CCOMP
The following section provides tables to show what CCOMP values
will provide the necessary compensation for given circuit configurations
and capacitive loads. In each case, the recommended CCOMP is a
minimum value. A larger CCOMP can always be used, but slew rate
and bandwidth performance will be degraded.
Figure 30 shows the AD744 configured as a unity gain voltage
follower. In this case, a minimum compensation capacitor of
5 pF is necessary for stable operation. Larger compensation ca-
pacitors can be used for driving larger capacitive loads. Table I
outlines recommended minimum values for CCOMP based on
the desired capacitive load. It also gives the slew rate and band-
width that will be achieved for each case.
AD744
1 F
0.1 F
–VS
CCOMP 5pF
1 F
0.1 F
+VS
VOUT
VIN
Figure 30. AD744 Connected as a Unity Gain
Voltage Follower
Table I. Recommended Values of CCOMP vs.
Various Capacitive Loads
Max
–3 dB
CLOAD
CCOMP
Slew Rate
Bandwidth
Gain
(pF)
(V/ s)
(MHz)
1
50
5
37
6.5
1
150
10
25
4.3
1
2000
25
12.5
2.0
Figures 31 and 32 show the AD744 as a voltage follower
with gain and as an inverting amplifier. In these cases, external
compensation is not necessary for stable operation. How-
ever, compensation may be applied to drive capacitive loads
above 50 pF. Table II gives recommended CCOMP values, along
with expected slew rates and bandwidths for a variety of load
conditions and gains for the circuits in Figures 31 and 32.
AD744
1 F
0.1 F
–VS
CCOMP
1 F
0.1 F
+VS
VOUT
VIN
OPTIONAL
R2*
CLEAD*
R1*
*SEE TABLE II
Figure 31. AD744 Connected as a Voltage Follower
Operating at Gains of 2 or Greater
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