Design & Operating Notes:
1. The ALD4702A/ALD4702B/ALD4702 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 ALD4702A/ALD4702B/ALD4702 is
internally compensated for unity gain stability using a novel scheme.
This design produces a clean single pole roll off in the gain character-
istics while providing for more than 70 degrees of phase margin at the
unity gain frequency. A unity gain buffer using the ALD4702A/
ALD4702B/ALD4702 will typically drive 400pF of external load capaci-
tance without stability problems. In the inverting unity gain configura-
tion, it can drive up to 800pF of load capacitance. Compared to other
CMOS operational amplifiers, the ALD4702A/ALD4702B/ALD4702 is
much more resistant to parasitic oscillations.
2. The ALD4702A/ALD4702B/ALD4702 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 selected
to be about 1.5V above the negative supply voltage. As offset voltage
trimming on the ALD4702A/ALD4702B/ALD4702 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 ALD4702A/ALD4702B/
ALD4702 an effective analog signal buffer for medium to high
source impedance sensors, transducers, and other circuit net-
works.
5. The ALD4702A/ALD4702B/ALD4702 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 100KΩ or
higher value resistor at the input terminals will limit input currents
to acceptable levels while causing very small or negligible accu-
racy 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 AS A FUNCTION
OF SUPPLY VOLTAGE AND TEMPERATURE
1000
±6
±5
±4
±3
±2
±1
0
0
OPEN LOOP VOLTAGE
GAIN (V/mV)
T
A
= 25°C
}
-55°C
}
+25°C
100
}
+125°C
10
R
L
= 10KΩ
R
L
= 5KΩ
1
±1
±2
±3
±4
±5
±6
±7
0
±2
±4
SUPPLY VOLTAGE (V)
±6
±8
SUPPLY VOLTAGE (V)
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
10000
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
12
INPUT BIAS CURRENT (pA)
1000
100
V
S
=
±
2.5V
SUPPLY CURRENT (mA)
10
8
INPUTS GROUNDED
OUTPUTS UNLOADED
T
A
= -55°C
6
4
2
0
10
-25°C
+25°C
+80°C
+125°C
1.0
0.1
-50
-25
0
25
50
75
100
125
±1
±2
±3
±4
±5
±6
AMBIENT TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
ALD4702A/ALD4702B
ALD4702
Advanced Linear Devices
4 of 9
ALD [ ADVANCED LINEAR DEVICES ]
