Design & Operating Notes:
1. The ALD4704A/ALD4704B/ALD4704 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 ALD4704A/ALD4704B/
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
ALD4704A/ALD4704B/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 ALD4704A/ALD4704B/
ALD4704 is much more resistant to parasitic oscillations.
2. The ALD4704A/ALD4704B/ALD4704 has complementary p-channel
and n-channel input differential stages connected in parallel to accom-
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 ALD4704A/ALD4704B/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 ALD4704A/ALD4704B/ALD4704 an effective analog sig-
nal buffer for medium to high source impedance sensors, transducers,
and other circuit networks.
5. The ALD4704A/ALD4704B/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 100KΩ or higher
value resistor at the input terminals will limit input currents to accept-
able levels while causing very small or negligible accuracy effects.
TYPICAL PERFORMANCE CHARACTERISTICS
COMMON MODE INPUT VOLTAGE RANGE
AS A FUNCTION OF SUPPLY VOLTAGE
±7
COMMON MODE INPUT
VOLTAGE RANGE (V)
OPEN LOOP VOLTAGE
GAIN (V/mV)
OPEN LOOP VOLTAGE GAIN AS A FUNCTION
OF SUPPLY VOLTAGE AND TEMPERATURE
1000
T
A
= 25°C
±6
±5
±4
±3
±2
±2
±3
±4
±5
±6
±7
SUPPLY VOLTAGE (V)
}
-55°C
}
+25°C
100
}
+125°C
10
R
L
= 10KΩ
R
L
= 5KΩ
1
0
±2
±4
SUPPLY VOLTAGE (V)
±6
±8
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
10000
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
8
7
6
5
4
3
2
1
T
A
= -55°C
-25°C
+25°C
+80°C
+125°C
INPUTS GROUNDED
OUTPUT UNLOADED
INPUT BIAS CURRENT (pA)
1000
100
V
S
=
±5.0V
10
1.0
0.1
-50
-25
0
25
50
75
100
125
SUPPLY CURRENT (mA)
0
0
±1
±2
±3
±4
±5
±6
±7
AMBIENT TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
ALD4704A/ALD4704B
ALD4704
Advanced Linear Devices
4 of 9
±7
INPUT
E (V)
±6
±5
ALD [ ADVANCED LINEAR DEVICES ]
