AD8601ART(Rev0) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
AD8601ART
(Rev.:Rev0)
(Rev.:Rev0)
Analog Devices
AD8601ART Datasheet PDF : 16 Pages
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AD8601/AD8602
5
4
VS = 5V
TA = 25؇C
3
2
1
0.1% 0.01%
0
0.1%
0.01%
؊1
؊2
؊3
؊4
؊5
0
200
400
600
800
SETTLING TIME – ns
1,000
TPC 49. Output Swing vs. Settling Time
THEORY OF OPERATION
The AD8601/AD8602 family of amplifiers are rail-to-rail input and
output precision CMOS amplifiers specified from 2.7 V to 5.0 V of
power supply voltage. These amplifiers use Analog Devices’ propri-
etary technology called DigiTrim™ to achieve a higher degree of
precision than available from most CMOS amplifiers. DigiTrim
technology is a method of trimming the offset voltage of the
amplifier after it has already been assembled. The advantage in
post-package trimming lies in the fact that it corrects any offset
voltages due to the mechanical stresses of assembly. This tech-
nology is scalable and utilized with every package option, including
SOT23-5, providing lower offset voltages than previously achieved in
these small packages.
The DigiTrim process is done at the factory and does not add
additional pins to the amplifier. All AD860x amplifiers are avail-
able in standard op amp pinouts, making DigiTrim completely
transparent to the user. The AD860x can be used in any preci-
sion op amp application.
The input stage of the amplifier is a true rail-to-rail architecture,
allowing the input common-mode voltage range of the op amp to
extend to both positive and negative supply rails. The voltage swing
of the output stage is also rail-to-rail and is achieved by using an
NMOS and PMOS transistor pair connected in a common-source
configuration. The maximum output voltage swing is proportional
to the output current, and larger currents will limit how close the
output voltage can get to the supply rail. This is a characteristic of
all rail-to-rail output amplifiers. With 1 mA of output current, the
output voltage can reach within 20 mV of the positive rail and
15 mV of the negative rail.
The open-loop gain of the AD860x is 100 dB, typical, with a load
of 2 kΩ. Because of the rail-to-rail output configuration, the gain
of the output stage, and thus the open-loop gain of the amplifier,
is dependent on the load resistance. Open-loop gain will decrease
with smaller load resistances. Again, this is a characteristic inher-
ent to all rail-to-rail output amplifiers.
Rail-to-Rail Input Stage
The input common-mode voltage range of the AD860x extends
to both positive and negative supply voltages. This maximizes
the usable voltage range of the amplifier, an important feature
DigiTrim is a trademark of Analog Devices.
for single supply and low voltage applications. This rail-to-rail
input range is achieved by using two input differential pairs, one
NMOS and one PMOS, placed in parallel. The NMOS pair is
active at the upper end of the common-mode voltage range, and
the PMOS pair is active at the lower end of the common-mode
range.
The NMOS and PMOS input stage are separately trimmed using
DigiTrim to minimize the offset voltage in both differential pairs.
Both NMOS and PMOS input differential pairs are active in a
500 mV transition region, when the input common-mode voltage
is between approximately 1.5 V and 1 V below the positive supply
voltage. Input offset voltage will shift slightly in this transition
region, as shown in Figures 5 and 6. Common-mode rejection
ratio will also be slightly lower when the input common-mode
voltage is within this transition band. Compared to the Burr
Brown OPA2340 rail-to-rail input amplifier, shown in Figure 1,
the AD860x, shown in Figure 2, exhibits lower offset voltage shift
across the entire input common-mode range, including the transi-
tion region.
0.7
0.4
0.1
؊0.2
؊0.5
؊0.8
؊1.1
؊1.4
0
1
2
3
4
5
VCM – V
Figure 1. Burr Brown OPA2340UR Input Offset Voltage
vs. Common-Mode Voltage, 24 SOIC Units @ 25°C
0.7
0.4
0.1
؊0.2
؊0.5
؊0.8
؊1.1
؊1.4
0
1
2
3
4
5
VCM – V
Figure 2. AD8602AR Input Offset Voltage vs.
Common-Mode Voltage, 300 SOIC Units @ 25°C
REV. 0
–13–
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