Low-Cost, High-Slew-Rate,
Rail-to-Rail I/O Op Amps in SC70
Pin Description
PIN
NAME
MAX4490
1
2
3
4
5
–
–
–
–
–
–
–
–
–
MAX4491
–
4
–
–
8
3
2
1
5
6
7
–
–
–
MAX4492
–
11
–
–
4
3
2
1
5
6
7
10, 12
9, 13
8, 14
IN+
V
SS
IN-
OUT
V
DD
INA+
INA-
OUTA
INB+
INB-
OUTB
INC+, IND+
INC-, IND-
OUTC, OUTD
Noninverting Input
Negative Supply Input. Connect to ground for single-supply operation.
Inverting Input
Amplifier Output
Positive Supply Input
Noninverting Input to Amplifier A
Inverting Input to Amplifier A
Amplifier A Output
Noninverting Input to Amplifier B
Inverting Input to Amplifier B
Amplifier B Output
Noninverting Inputs to Amplifiers C and D
Inverting Inputs to Amplifiers C and D
Amplifiers C and D Outputs
FUNCTION
MAX4490/MAX4491/MAX4492
Detailed Description
Rail-to-Rail Input Stage
The MAX4490/MAX4491/MAX4492 CMOS operational
amplifiers have parallel-connected N- and P-channel
differential input stages that combine to accept a com-
mon-mode range extending to both supply rails. The N-
channel stage is active for common-mode input
voltages typically greater than (V
SS
+ 1.2V), and the P-
channel stage is active for common-mode input volt-
ages typically less than (V
DD
- 1.2V).
when the load is connected to V
DD
/2. Consistent resis-
tive drive capability is (2.5 - 0.1) / 2.2 = 1.1kΩ. For the
same application, resistive drive capability is 2.2kΩ
when the load is connected to V
DD
or V
SS
.
Applications Information
Power-Supply Considerations
The MAX4490/MAX4491/MAX4492 operate from a sin-
gle +2.7V to +5.5V supply or from dual ±1.35V to
±2.75V supplies with typically 800µA supply current
per amplifier. A high power-supply rejection ratio of
100dB allows for extended operation from a decaying
battery voltage, thereby simplifying designs for
portable applications. For single-supply operation,
bypass the power supply with a 0.1µF ceramic capaci-
tor placed close to the V
DD
pin. For dual-supply opera-
tion, bypass each supply to ground.
Rail-to-Rail Output Stage
The MAX4490/MAX4491/MAX4492 CMOS operational
amplifiers feature class-AB push-pull output stages that
can drive a 100kΩ load to within 1.5mV of either supply
rail. Short-circuit output current is typically ±50mA.
Figures 1a and 1b show the typical temperature depen-
dence of output source and sink currents, respectively,
for three fixed values of (V
DD
- V
OH
) and (V
OL
- V
SS
).
For example, at V
DD
= +5.0V, the load currents that
maintain (V
DD
- V
OH
) = 100mV and (V
OL
- V
SS
) = 100mV
at T
A
= +25°C are 2.2mA and 3.3mA, respectively,
Input Capacitance
One consequence of the parallel-connected differential
input stages for rail-to-rail operation is a relatively large
input capacitance C
IN
(typically 5pF). This introduces a
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