LM363 Datasheet, PDF (12/22 Pages) National Semiconductor (TI) – LM363 Precision Instrumentation Amplifier

Application Hints (Continued)
COMPENSATION AND OUTPUT CLAMPING
The LM363 is internally compensated for unity feedback
from output to sense Increasing gain with external dividers
will decrease the bandwidth and increase stability margin
Without external compensation the amplifier can stably
drive capacitive loads up to 400 pF When used as an op
amp (sense and reference pins grounded feedback to in-
verting input) the LM363 is stable for gains of 100 or more
For greater stability the device may be over-compensated
as in Figure 6 Tables I and II depict suggested compensa-
tion components along with the resulting changes in large
and small signal bandwidth for the 8-pin and 16-pin pack-
ages respectively
Note that the RC network from pin 8 of the 8-pin device to
ground has a large effect on power bandwidth especially at
low gains The Miller capacitance utilized for overcompen-
sating the 16-pin device permits higher slew rate and larger
load capacitance for the same bandwidth and is preferred
when bandwidth must be greatly reduced (e g to reduce
output noise)
Heavy Miller overcompensation on the 16-pin package can
degrade AC PSRR A large capacitor between pins 15 and
16 couples transients on the positive supply to the output
buffer Since the amplifier bandwidth is severely rolled off it
cannot keep the output at the correct state at moderate
frequencies Hence for good PSRR either keep the Miller
capacitance under 1000 pF or use the pin 15-to-ground
compensation shown in Table I
TL H 5609 – 14
FIGURE 6 Overcompensation
TABLE I Overcompensation on 8-Pin Package
Gain
500
100
10
Compensation Network
(Pin 8 to Ground)
100 pF 15k
1000 pF 5k
0 01 mF 500X
0 1 mF
100 pF 15k
1000 pF 5k
0 01 mF 500X
0 1 mF
100 pF 15k
1000 pF 5k
0 01 mF 500X
0 1 mF
Small Signal
3 dB
Bandwidth
(kHz)
125
95
45
10
1
240
170
80
20
2
240
170
90
20
2
Power
Bandwidth
(g10V Swing)
(Hz)
100k
15k
1 8k
200
20
100k
15k
1 8k
200
20
100k
15k
1 8k
200
20
Maximum
Capacitive
Load
(pF)
400
600
800
1000
1000
400
900
1200
1600
2000
400
900
1200
1600
2000
Also stable for C_L t 0 05 mF
Pin 15 to ground on 16-pin package
TABLE II Overcompensation on 16-Pin Package
Gain
Compensation
Capacitor
(Pin 15 to 16)
1000
10 pF
100 pF
1000 pF
0 01 mF
10 pF
100
100 pF
1000 pF
0 01 mF
10 pF
10
100 pF
1000 pF
0 01 mF
Also stable for C_L t 0 05 mF
Small Signal
3 dB
Bandwidth
(Hz)
45k
16k
2 5k
250
25
140k
50k
7 5k
750
75
180k
60k
9k
900
90
Power
Bandwidth
(g10V Swing)
(Hz)
45k
16k
2 5k
250
25
100k
50k
7 5k
750
75
90k
50k
9k
900
90
Maximum
Capacitive
Load
(pF)
1000
2000
2500
3000
3000
900
1600
2000
2000
2000
600
1100
1600
2000
2000
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