Low-Cost, High-Slew-Rate,
Rail-to-Rail I/O Op Amps in SC70
MAX4490/MAX4491/MAX4492
pole at frequency (2πR′C
IN
)
-1
, where R′ is the parallel
combination of the gain-setting resistors for the invert-
ing or noninverting amplifier configuration (Figure 2). If
the pole frequency is less than or comparable to the
unity-gain bandwidth (10MHz), the phase margin will
be reduced, and the amplifier will exhibit degraded
AC performance through either ringing in the step
response or sustained oscillations. The pole frequency is
10MHz when R′ = 3.2kΩ. To maximize stability, R′ <3kΩ
is recommended.
Applications that require rail-to-rail operation with mini-
mal loading (for small V
DD
- V
OH
and V
OL
- V
SS
) will
typically require R′ values >3kΩ. To improve step
response under these conditions, connect a small
capacitor C
f
between the inverting input and output.
Choose C
f
as follows:
C
f
= 5(R / R
f
) [pf]
where R
f
is the feedback resistor and R is the gain-set-
ting resistor (Figure 2).
Figure 3 shows the step response for a noninverting
amplifier subject to R′ = 4kΩ with and without the C
f
feedback capacitor.
6
OUTPUT SOURCE CURRENT (mA)
5
4
3
2
1
0
-40 -25 -10 5
V
DD
= +2.7V
INVERTING
V
DD
- V
OH
= 200mV
V
DD
- V
OH
= 100mV
V
DD
- V
OH
= 50mV
V
DD
= +5.0V
R
V
OUT
C
f
R
f
V
IN
MAX4490
R′ = R || R
f
R
f
C
f
= RC
IN
20 35 50 65 80 95 110 125
TEMPERATURE (°C)
Figure 1a. Output Source Current vs. Temperature
NONINVERTING
V
IN
9
8
OUTPUT SINK CURRENT (mA)
7
6
5
4
3
2
1
0
V
DD
= +2.7V
V
DD
- V
OH
= 200mV
V
DD
- V
OH
= 100mV
V
DD
- V
OH
= 50mV
V
DD
= +5.0V
V
OUT
MAX4490
R
f
C
f
R
R′ = R || R
f
R
f
C
f
= RC
IN
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
Figure 2. Inverting and Noninverting Amplifier with Feedback
Compensation
Figure 1b. Output Sink Current vs. Temperature
6
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
