Chip information – Rainbow Electronics MAX4492 User Manual
Page 7
Driving Capacitive Loads
In conjunction with op amp output resistance, capaci-
tive loads introduce a pole frequency that can reduce
phase margin and lead to unstable operation. The
MAX4490/MAX4491/MAX4492 drive capacitive loads
up to 300pF without significant degradation of step
response and slew rate (Figure 4). Capacitive-Load
Stability (page 1) shows regions of stable and margin-
ally stable (step overshoot <10%) operation for different
combinations of capacitive and resistive loads.
Improve stability for large capacitive loads by adding
an isolation resistor (typically 10
Ω) in series with the
output (Figure 5). Note that the isolation resistor forms a
voltage divider with potential for gain error.
Chip Information
MAX4490 TRANSISTOR COUNT: 60
MAX4491 TRANSISTOR COUNT: 120
MAX4492 TRANSISTOR COUNT: 240
SUBSTRATE CONNECTED TO V
SS
MAX4490/MAX4491/MAX4492
Low-Cost, High-Slew-Rate,
Rail-to-Rail I/O Op Amps in SC70
_______________________________________________________________________________________
7
Figure 4. Step Response With and Without Capacitive Loading
A
V
= +1, R
L
= 100k
Ω, C
L
= 0
4a)
4b)
WITHOUT CAPACITIVE LOADING
WITH CAPACITIVE LOADING
A
V
= +1, R
L
= 100k
Ω, C
L
= 300pF
Figure 3. Step Response With and Without Feedback
Compensation
A
V
= -1, R
L
= 4k
Ω, C
f
= 0
3a)
3b)
WITHOUT FEEDBACK COMPENSATION
WITH FEEDBACK COMPENSATION
A
V
= -1, R
L
= 4k
Ω, C
f
= 5pF