REV. C
AD744
–9–
Table II. Recommended Values of CCOMP vs. Various Load Conditions for the Circuits of
Figures 31 and 32.
Max
Slew
–3 dB
R1
R2
Gain
CLOAD
CCOMP
CLEAD
Rate
Bandwidth
( )( )
Follower
Inverter
(pF)
(V/ s)
(MHz)
4.99 k
2
1
50
0
7
75
2.5
1
4.99 k
2
1
150
5
7
37
2.31
4.99 k
2
1
1000
20
–
14
1.2
4.99 k
2
1
>2000
25
–
12.5
2
1.0
499
4.99 k
11
10
270
0
–
75
1.2
499
4.99 k
11
10
390
2
–
50
0.85
499
4.99 k
11
10
1000
5
–
37
2
0.60
NOTES
1Bandwidth with C
LEAD adjusted for minimum settling time.
2Into large capacitive loads the AD744’s 25 mA output current limit sets the slew rate of the amplifier, in V/
s, equal to 0.025
amps divided by the value of CLOAD in
F. Slew rate is specified into rated max C
LOAD except for cases marked
2, which are
specified with a 50 pF. load.
AD744
1 F
0.1 F
–VS
CCOMP
1 F
0.1 F
+VS
VOUT
VIN
OPTIONAL
R2*
CLEAD*
R1*
*SEE TABLE II
Figure 32. AD744 Connected as an Inverting Amplifier
Operating at Gains of 1 or Greater
Using Decompensation to Extend the Gain Bandwidth
Product
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, CCOMP, effectively dec-
ompensating the amplifier.
Due to manufacturing variations in the value of the internal
CCOMP, 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.
\
AD744
1 F
0.1 F
–VS
1 F
0.1 F
+VS
VOUT
VIN
NOT CONNECTED
R2*
R1*
2 – 10pF
*SEE TABLE III
Figure 33. Using the Decompensation Connection to
Extend Gain Bandwidth
Table III. Performance Summary for the Circuit of Figure 33
R1
R2
Gain
–3 dB
Gain/BW
( )( )
Follower
Inverter
Bandwidth
Product
1 k
10 k
11
10
2.5 MHz
25 MHz
100
10 k
101
100
760 kHz
76 MHz
100
100 k
1001
1000
225 kHz
225 MHz