ALD4701A/ALD4701B

Advanced Linear Devices

4 of 9

ALD4701

TYPICAL PERFORMANCE CHARACTERISTICS

INPUT BIAS CURRENT AS A FUNCTION

OF AMBIENT TEMPERATURE

AMBIENT TEMPERATURE (°C)

1000

100

10

0.1

1.0

100

-25

0

75

125

50

25

-50

10000

OPEN LOOP VOLTAGE GAIN AS A

FUNCTION OF LOAD RESISTANCE

10M

LOAD RESISTANCE (Ω)

10K

100K

1M

1000

100

10

1

COMMON MODE INPUT VOLTAGE RANGE

AS A FUNCTION OF SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

±7

±6

±5

±4

±3

±2

±1

0

0

±1

±2

±3

±4

±5

±6

±7

Design & Operating Notes:

1. The ALD4701A/ALD4701B/ALD4701 CMOS operational amplifier uses

a 3 gain 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 capaci-

tor 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 ALD4701A/ALD4701B/ALD4701 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.

2. The ALD4701A/ALD4701B/ALD4701 has complementary p-channel

and n-channel input differential stages connected in parallel to accom-

plish rail-to-rail input common mode voltage range. 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 ALD4701A/ALD4701B/

ALD4701 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 above 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 provision in his design to allow for input offset voltage variations.

3. The input bias and offset currents are essentially input protection diode

reverse bias leakage currents, and are typically less than 1pA at room

temperature. This low input bias current assures that the analog signal

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

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.

4. The output stage consists of class AB complementary output drivers,

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.

5. The ALD4701A/ALD4701B/ALD4701 operational amplifier has been

designed to 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.

6. The ALD4701A/ALD4701B/ALD4701, with its micropower operation,

offers 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 0.4°C above ambient temperature under most operating condi-

tions.

SUPPLY CURRENT AS A FUNCTION

OF SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

1600

800

1200

0

400

0

±1

±2

±3

±4

±5

±6

+25°C

+70°C

+125°C

INPUTS GROUNDED

OUTPUT UNLOADED

-25°C