__________Applications Information

Rail-to-Rail Inputs and Outputs

The MAX4162/MAX4163/MAX4164 input common-mode

range extends 250mV beyond each of the supply rails,

providing a substantial increase in dynamic range over

other op amps (even many of those referred to as rail-to-

rail). Although the minimum operating voltage is speci-

fied at 2.5V, the devices typically provide full rail-to-rail

operation below 2.0V (Figure 1). These amplifiers do not

suffer from midswing common-mode-rejection degrada-

tion or crossover nonlinearity often encountered in other

rail-to-rail op amps. Extremely low, 1.0pA input bias cur-

rent makes these devices ideal for applications such as

pH probes, electrometers, and ionization detectors.

They are also protected against phase reversal (inferred

from CMRR test) and latchup for input signals extending

beyond the supply rails. The output stage achieves a

lower output impedance than traditional rail-to-rail out-

put stages, providing an output voltage range that typi-

cally swings within 150mV of the supply rails for 1mA

loads. This architecture also maintains high open-loop

gain and output swing while driving substantial loads.

Output Loading and Stability

These devices drive 1mA loads to within 150mV of the

supply rails while consuming only 25µA of quiescent

current. Internal compensation allows these amplifiers to

remain unity-gain stable while driving any capacitive

load (Figure 2).

Internal Charge Pump

An internal charge pump provides two internal supplies

typically 2V beyond each rail. These internal rails allow

the MAX4162/MAX4163/MAX4164 to achieve true rail-

to-rail inputs and outputs, while providing excellent

common-mode rejection, power-supply rejection ratios,

and gain linearity.

These charge pumps require no external components,

and in most applications are entirely transparent to the

user. Two characteristics may be visible to the user,

depending on the application:

UCSP, Micropower, Single-Supply, 10V,

Rail-to-Rail I/O Op Amps

10

______________________________________________________________________________________

IN

200mV/div

500mV

0

500mV

0

OUT

200mV/div

LARGE CAPACITIVE-LOAD DRIVE

MAX4162-36

5µs/div

Figure 2. Large Capacitive-Load Drive

IN

0.667V/div

2V

0

2V

0

OUT

0.667V/div

RAIL-TO-RAIL

INPUT/OUTPUT VOLTAGE RANGE

MAX4162-34

200µs/div

IN

1V/div

3V

0

3V

0

OUT

1V/div

RAIL-TO-RAIL

INPUT/OUTPUT VOLTAGE RANGE

MAX4162-35

200µs/div

a)

b)