Design & Operating Notes:
1. The 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 ALD4702 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 ALD4702 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 ALD4702 is much more
resistant to parasitic oscillations.
2. The ALD4702 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 opera-
tional amplifiers, this switching point has been selected to be about
1.5V above the negative supply voltage. As offset voltage trimming on
the 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 ALD4702 an
effective analog signal buffer for medium to high source imped-
ance sensors, transducers, and other circuit networks.
5. The 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 accuracy effects.
TYPICAL PERFORMANCE CHARACTERISTICS
COMMON MODE INPUT VOLTAGE RANGE
AS A FUNCTION OF SUPPLY VOLTAGE
±7
±6
COMMON MODE INPUT
)
VOLTAGE RANGE (V
OPEN LOOP VOLTAGE GAIN AS A FUNCTION
OF SUPPLY VOLTAGE AND TEMPERATURE
1000
} -55°C
T
A
= 25°C
OPEN LOOP VOLTAGE
GAIN (V/mV)
±5
±4
±3
±2
±1
0
0
±1
±2
±3
±4
±5
±6
±7
} +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
12
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
SUPPLY CURRENT (mA)
10
8
T
A
= -55°C
6
4
2
0
-25°C
+25°C
+80°C
+125°C
INPUTS GROUNDED
OUTPUTS UNLOADED
INPUT BIAS CURRENT (pA)
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)
ALD4702A/ALD4702B
ALD4702
Advanced Linear Devices
4
ALD [ ADVANCED LINEAR DEVICES ]
