ALD4704A/ALD4704B

Advanced Linear Devices

4

ALD4704

TYPICAL PERFORMANCE CHARACTERISTICS

Design & Operating Notes:

1. The ALD4704 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 ALD4704 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 ALD4704 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 ALD4704 is much more

resistant to parasitic oscillations.

2. The ALD4704 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 opera-

tional amplifiers, this switching point has been selected to be about

1.5V above the negative supply voltage. As offset voltage trimming on

the ALD4704 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 neces-

sary 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 ALD4704 an effective analog signal buffer for medium to

high source impedance sensors, transducers, and other circuit net-

works.

5. The ALD4704 operational amplifier has been designed with static

discharge protection and 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.

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

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

SUPPLY CURRENT AS A FUNCTION

OF SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

0

0

±1

±2

±3

±4

±5

±6

+80

°C

+25

°C

-25

°C

±7

2

4

6

8

10

12

14

16

INPUTS GROUNDED

OUTPUT UNLOADED

+125

°C

COMMON MODE INPUT VOLTAGE RANGE

AS A FUNCTION OF SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

±7

±6

±5

±4

±3

±2

±2

±3

±4

±5

±6

±7