ALD1731A/ALD1731

Advanced Linear Devices

4 of 9

Design & Operating Notes:

stage architecture and an improved frequency compensation

scheme to achieve large voltage gain, high output driving capability,

and better frequency stability. In a conventional CMOS operational

amplifier design, compensation is achieved with a pole splitting

capacitor together with a nulling resistor. This method is, however,

very bias dependent and thus cannot accommodate the large range

of supply voltage operation as is required from a stand alone CMOS

operational amplifier. The ALD1731A/ALD1731 is internally compen-

sated for unity gain stability using a novel scheme that does not use

a nulling resistor. This scheme produces a clean single pole roll off

in the gain characteristics while providing for more than 70 degrees

of phase margin at the unity gain frequency.

channel input differential stages connected in parallel to accomplish

rail to rail common mode input voltage ranges. This means that with

the ranges of common mode input voltage close to the power

supplies, one of the two differential stages is switched off internally.

To maintain compatibility with other operational amplifiers, this

switching point has been selected to be about 1.5V below the positive

supply voltage. Since offset voltage trimming on the ALD1731A/

ALD1731 is made when the input voltage is symmetrical to the supply

voltages, this internal switching does not affect a large variety of

applications such as an inverting amplifier or non-inverting amplifier

with a gain larger than 2.5 (5V operation), where the common mode

voltage does not make excursions below this switching point. The

user should, however, be aware that this switching does take place if

the operational amplifier is connected as a unity gain buffer and

should make provisions in the design to allow for input offset voltage

variations.

temperature. This low input bias current assures that the analog

signal from the source will not be distorted by input bias currents.

would not be a problem as the source impedance would limit the node

impedance. However, for applications where source impedance is

very high, it may be necessary to limit noise and hum pickup through

proper shielding.

capable of driving a low resistance load. The output voltage swing is

limited by the drain to source on-resistance of the output transistors

as determined by the bias circuitry, and the value of the load resistor.

When connected in the voltage follower configuration, the oscillation

resistant feature, combined with the rail to rail input and output

feature, makes an effective analog signal buffer for medium to high

source impedance sensors, transducers, and other circuit networks.

provide full static discharge protection. Internally, the design has

been carefully implemented to minimize latch up. However, care must

be exercised when handling the device to avoid strong static fields

that may degrade a diode junction, causing increased input leakage

currents. In using the operational amplifier, the user is advised to

power up the circuit before, or simultaneously with, any input voltages

applied and to limit input voltages not to exceed 0.3V of the power

supply voltage levels.

numerous benefits in reduced power supply requirements, less

noise coupling and current spikes, less thermally induced drift,

better overall reliability due to lower self heating, and lower input

bias current. It requires practically no warm up time as the chip

junction heats up to only 0.1°C above ambient temperature under

most operating conditions.

provides robust high temperature operation. Contact factory for

custom screening versions.

TYPICAL PERFORMANCE CHARACTERISTICS

COMMON MODE INPUT VOLTAGE RANGE

AS A FUNCTION OF SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

±5

±3

0

±1

±4

±2

0

±1

±2

±3

±4

±5

±6

±6

OPEN LOOP VOLTAGE GAIN AS A

FUNCTION OF LOAD RESISTANCE

LOAD RESISTANCE (Ω)

10M

10K

100K

1M

1000

100

10

1

SUPPLY CURRENT AS A FUNCTION

OF SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

500

300

0

100

400

200

0

±1

±2

±3

±4

±5

±6

+25°C

+70°C

+125°C

INPUTS GROUNDED

OUTPUT UNLOADED

-25°C

INPUT BIAS CURRENT AS A FUNCTION

OF AMBIENT TEMPERATURE

AMBIENT TEMPERATURE (°C)

100

10

1.0

0.01

0.1

1000

+100

-25

0

+75

+125

+50

+25

-50