ADA4665-2ARZ-RL Analog Devices Inc, ADA4665-2ARZ-RL Datasheet - Page 15

• Manufacturer Part Number: ADA4665-2ARZ-RL
• Description: 2.7V-16V Dual RR CMOS (non-precision)
• Manufacturer: Analog Devices Inc

Specifications of ADA4665-2ARZ-RL

• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Slew Rate: 1 V/µs
• Gain Bandwidth Product: 1.2MHz
• Current - Input Bias: 0.1pA
• Voltage - Input Offset: 1000µV
• Current - Supply: 290µA
• Current - Output / Channel: 30mA
• Voltage - Supply, Single/dual (±): 5 V ~ 16 V, ±2.5 V ~ 8 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
RAIL-TO-RAIL INPUT OPERATION
The ADA4665-2 is a unity-gain stable CMOS operational
amplifier designed with rail-to-rail input/output swing
capability to optimize performance. The rail-to-rail input
feature is vital to maintain the wide dynamic input voltage
range and to maximize signal swing to both supply rails. For
example, the rail-to-rail input feature is extremely useful in
buffer applications where the input voltage must cover both
the supply rails.
The input stage has two input differential pairs, nMOS and
pMOS. When the input common-mode voltage is at the low
end of the input voltage range, the pMOS input differential pair
is active and amplifies the input signal. As the input common-
mode voltage is slowly increased, the pMOS differential pair
gradually turns off while the nMOS input differential pair turns
on. This transition is inherent to all rail-to-rail input amplifiers
that use the dual differential pairs topology. For the ADA4665-2,
this transition occurs approximately 1 V away from the positive
rail and results in a change in offset voltage due to the different
offset voltages of the differential pairs (see Figure 5 and Figure 8).
CURRENT SHUNT SENSOR
Many applications require the sensing of signals near the
positive or the negative rails. Current shunt sensors are one
such application and are mostly used for feedback control
systems. They are also used in a variety of other applications,
including power metering, battery fuel gauging, and feedback
controls in electrical power steering. In such applications, it is
desirable to use a shunt with very low resistance to minimize
the series voltage drop. This not only minimizes wasted power,
but also allows the measurement of high currents while saving
power. The ADA4665-2 provides a low cost solution for
implementing current shunt sensors.
Figure 55 shows a low-side current sensing circuit, and Figure 56
shows a high-side current sensing circuit using the ADA4665-2.
A typical shunt resistor of 0.1 Ω is used. In these circuits, the
difference amplifier amplifies the voltage drop across the shunt
resistor by a factor of 100. For true difference amplification,
matching of the resistor ratio is very important, where R1/R2 =
R3/R4. The rail-to-rail feature of the ADA4665-2 allows the
output of the op amp to almost reach 16 V (the power supply of
the op amp). This allows the current shunt sensor to sense up to
approximately 1.6 A of current.
Rev. 0 | Page 15 of 20
ACTIVE FILTERS
The ADA4665-2 is well suited for active filter designs. An active
filter requires an op amp with a unity-gain bandwidth at least
100 times greater than the product of the corner frequency, f
and the quality factor, Q. An example of an active filter is the
Sallen-Key, one of the most widely used filter topologies. This
topology gives the user the flexibility of implementing either
a low-pass or a high-pass filter by simply interchanging the
resistors and capacitors. To achieve the desired performance,
1% or better component tolerances are usually required.
Figure 57 shows a two-pole low-pass filter. It is configured as a
unity-gain filter with cutoff frequency at 10 kHz. Resistor and
capacitor values are chosen to give a quality factor, Q, of 1/√2
for a Butterworth filter, which has maximally flat pass-band
frequency response. Figure 58 shows the frequency response of
the low-pass Sallen-Key filter. The response falls off at a rate of
40 dB per decade after the cutoff frequency of 10 kHz.
V
*V
V
*V
SUPPLY
SUPPLY
OUT
OUT
OUT
OUT
16V
16V
*
*
= AMPLIFIER GAIN × VOLTAGE ACROSS R
= 100 × R
= 10 × I
= AMPLIFIER GAIN × VOLTAGE ACROSS R
= 100 × R
= 10 × I
ADA4665-2
ADA4665-2
Figure 56. High-Side Current Sensing Circuit
Figure 55. Low-Side Current Sensing Circuit
S
S
× I
× I
1MΩ
1MΩ
1MΩ
1MΩ
R4
R2
R2
R4
16V
16V
1/2
1/2
I
I
I
I
10kΩ
10kΩ
10kΩ
10kΩ
R3
R1
R1
R3
0.1Ω
0.1Ω
R
R
S
S
S
S
ADA4665-2
R
R
L
L
c
,