Design & Operating Notes:
1. The ALD2702A/ALD2702B/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 ALD2702A/
ALD2702B/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 ALD2702A/ALD2702B/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 ALD2702A/ALD2702B/ALD2702 has
shown itself to be more resistant to parasitic oscillations.
2. The ALD2702A/ALD2702B/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 ALD2702A/ALD2702B/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 ALD2702A/ALD2702B/ALD2702 an effective analog signal
buffer for medium to high source impedance sensors, transducers,
and other circuit networks.
5. The ALD2702A/ALD2702B/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
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
6
SUPPLY CURRENT (mA)
INPUT BIAS CURRENT (pA)
1000
100
V
S
=
±
2.5V
5
4
INPUTS GROUNDED
OUTPUTS UNLOADED
T
A
= -55°C
3
2
1
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)
ALD2702A/ALD2702B
ALD2702
Advanced Linear Devices
4 of 9
ALD [ ADVANCED LINEAR DEVICES ]
