ALD2702A/ALD2702B

Advanced Linear Devices

4

ALD2702

Design & Operating Notes:

1. The ALD2702 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. The ALD2702 is internally compensated

for unity gain stability using a novel scheme. This design 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. A unity gain buffer using the ALD2702 will typically

drive 400pF of external load capacitance without stability problems.

In the inverting unity gain configuration, it can drive up to 800pF

of load capacitance.

Compared to other CMOS operational

amplifiers, the ALD2702 has shown itself to be more resistant to

parasitic oscillations.

2. The ALD2702 has complementary p-channel and n-channel input

differential stages connected in parallel to accomplish rail-to-rail input

common mode voltage range. With the 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

above the negative supply voltage. As offset voltage trimming on the

ALD2702 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 greater than 2.5 (5V operation), where the common mode

voltage does not make excursions below this switching point.

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. 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 the ALD2702 an effective analog signal buffer for medium to

high source impedance sensors, transducers, and other circuit

networks.

5. The ALD2702 operational amplifier has been designed with 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. 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 to not exceed 0.3V of the power supply voltage levels.

Alternatively, a 100K

Ω or higher value resistor at the input terminals

will limit input currents to acceptable levels while causing very small

or negligible accuracy effects.

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 SUPPLY VOLTAGE AND TEMPERATURE

SUPPLY VOLTAGE (V)

1000

100

10

1

0

±2

±4

±6

} -55

°C

} +25

°C

} +125

°C

±8

SUPPLY CURRENT AS A FUNCTION

OF SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

6

5

4

3

1

2

0

±6

±5

±4

±3

±1

±2

INPUTS GROUNDED

OUTPUTS UNLOADED

-25

°C

+80

°C

+125

°C

+25

°C

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