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 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
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
±5
±4
±3
±2
±1
0
0
±1
±2
±3
±4
±5
±6
±7
OPEN LOOP VOLTAGE
GAIN (V/mV)
±6
T
A
= 25°C
} -55°C
} +25°C
100
} +125°C
10
R
L
= 10KΩ
R
L
= 5KΩ
1
0
±2
±4
SUPPLY VOLTAGE (V)
±6
±8
SUPPLY VOLTAGE (V)
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
10000
INPUT BIAS CURRENT (pA)
6
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
SUPPLY CURRENT (mA)
5
4
3
2
1
0
INPUTS GROUNDED
OUTPUTS UNLOADED
T
A
= -55°C
-25°C
+25°C
+80°C
+125°C
1000
100
V
S
=
±
2.5V
10
1.0
0.1
-50
-25
0
25
50
75
100
125
±1
±2
±3
±4
±5
±6
AMBIENT TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
ALD2702A/ALD2702B
ALD2702
Advanced Linear Devices
4
ALD [ ADVANCED LINEAR DEVICES ]
