AD744
Table II. Recommended Values of C
COMP
vs. Various Load Conditions for the Circuits of
Figures 31 and 32.
R1
( )
4.99 k
4.99 k
4.99 k
4.99 k
499
Ω
499
Ω
499
Ω
R2
( )
4.99 k
4.99 k
4.99 k
4.99 k
4.99 k
4.99 k
4.99 k
Gain
Follower
2
2
2
2
11
11
11
Gain
Inverter
1
1
1
1
10
10
10
Max
C
LOAD
(pF)
50
150
1000
>2000
270
390
1000
C
COMP
(pF)
0
5
20
25
0
2
5
C
LEAD
(pF)
7
7
–
–
–
–
–
Slew
Rate
(V/ s)
75
37
14
12.5
2
75
50
37
2
–3 dB
Bandwidth
(MHz)
2.5
1
2.3
1
1.2
1.0
1.2
0.85
0.60
NOTES
1
Bandwidth with C
LEAD
adjusted for minimum settling time.
2
Into large capacitive loads the AD744’s 25 mA output current limit sets the slew rate of the amplifier, in V/
µs,
equal to 0.025
amps divided by the value of C
LOAD
in
µF.
Slew rate is specified into rated max C
LOAD
except for cases marked
2
, which are
specified with a 50 pF. load.
C
LEAD
*
R2*
+V
S
R1*
V
IN
1 F
0.1 F
Due to manufacturing variations in the value of the internal
C
COMP
, it is recommended that the amplifier’s response be
optimized for the desired gain by using a 2 to 10 pF trimmer
capacitor rather than using a fixed value.
R1*
R2*
+V
S
1 F
0.1 F
AD744
OPTIONAL
C
COMP
*SEE
TABLE II
1 F
–V
S
0.1 F
V
OUT
AD744
V
OUT
NOT CONNECTED
2 – 10pF
*SEE
TABLE III
Figure 32. AD744 Connected as an Inverting Amplifier
Operating at Gains of 1 or Greater
Using Decompensation to Extend the Gain Bandwidth
Product
\
V
IN
1 F
–V
S
0.1 F
When the AD744 is used in applications where the closed-loop
gain is greater than 10, gain bandwidth product may be enhanced
by connecting a small capacitor between Pins 1 and 5 (Figure
33). At low frequencies, this capacitor cancels the effects of the
chip’s internal compensation capacitor, C
COMP
, effectively dec-
ompensating the amplifier.
Figure 33. Using the Decompensation Connection to
Extend Gain Bandwidth
Table III. Performance Summary for the Circuit of Figure 33
R1
( )
1k
100
100
R2
( )
Gain
Follower
Gain
Inverter
10
100
1000
–3 dB
Bandwidth
2.5 MHz
760 kHz
225 kHz
Gain/BW
Product
25 MHz
76 MHz
225 MHz
10 k 11
10 k 101
100 k 1001
REV. C
–9–
AD [ ANALOG DEVICES ]
