Design & Operating Notes:
3. Theinputbiasandoffsetcurrentsareessentiallyinputprotectiondiode
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
applicationswheresourceimpedanceisveryhigh,itmaybenecessary
to limit noise and hum pickup through proper shielding.
1. The ALD2704A/ALD2704B/ALD2704 CMOS operational amplifier
uses a 3 gain stage architecture and an improved frequency compen-
sation scheme to achieve large voltage gain, high output driving
capability, and better frequency stability. The ALD2704A/ALD2704B/
ALD2704 is internally compensated for unity gain stability using a
novel scheme. This design produces a clean single pole roll off in the
gaincharacteristicswhileprovidingformorethan70degreesofphase
margin at the unity gain frequency. A unity gain buffer using the
ALD2704A/ALD2704B/ALD2704 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 ALD2704A/ALD2704B/
ALD2704 is much more resistant to parasitic oscillations.
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. The
voltagefollowerconfiguration, theoscillationandresistantwiththerail-
to-rail input and output feature, makes the ALD2704A/ALD2704B/
ALD2704 an effective analog signal buffer for medium to high source
impedance sensors, transducers, and other circuit networks.
2. The ALD2704A/ALD2704B/ALD2704 has complementary p-channel
andn-channelinputdifferentialstagesconnectedinparalleltoaccom-
plish 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 se-
lected to be about 1.5V above the negative supply voltage. As offset
voltage trimming on the ALD2704A/ALD2704B/ALD2704 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 (10V operation), where the common mode voltage does not
make excursions below this switching point.
5. The ALD2704A/ALD2704B/ALD2704 operational amplifier has been
designed to provide 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 100KΩ 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
OPEN LOOP VOLTAGE GAIN AS A FUNCTION
OF SUPPLY VOLTAGE AND TEMPERATURE
COMMON MODE INPUT VOLTAGE RANGE
AS A FUNCTION OF SUPPLY VOLTAGE
1000
±7
}
}
-55°C
+25°C
T
= 25°C
A
±6
100
±5
±4
±3
}
+125°C
10
1
R = 10KΩ
L
R = 5KΩ
L
±2
0
±2
±4
SUPPLY VOLTAGE (V)
±6
±8
±3
±5
SUPPLY VOLTAGE (V)
±2
±4
±6
±7
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
10000
8
7
INPUTS GROUNDED
OUTPUT UNLOADED
V
S
= ±5.0V
1000
100
6
5
4
3
2
T
A
= -55°C
-25°C
+25°C
10
+80°C
+125°C
1.0
0.1
1
0
-50 -25
0
25
50
75
100
125
0
±1
±2
±3
±4
±5
±6
±7
AMBIENT TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
ALD2704A/ALD2704B
ALD2704
Advanced Linear Devices
4 of 9
ALD [ ADVANCED LINEAR DEVICES ]
