A
DVANCED
L
INEAR
D
EVICES,
I
NC.
TM
ALD2726E/ALD2726
e
®
EPAD
D
LE
AB
E
N
DUAL EPAD® ULTRA MICROPOWER CMOS OPERATIONAL AMPLIFIER
KEY FEATURES
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•
•
•
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•
•
•
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•
EPAD (Electrically Programmable Analog Device)
User programmable V
OS
trimmer
Computer-assisted trimming
Rail-to-rail input/output
Compatible with standard EPAD Programmer
Each amplifier V
OS
can be trimmed to a different V
OS
level
High precision through in-system circuit precision trimming
Reduces or eliminates V
OS
, PSRR, CMRR and TCV
OS
errors
System level “calibration” capability
Application Specific Programming mode
In-System Programming mode
Electrically programmable to compensate for external
component tolerances
• Achieves 0.01pA input bias current and 35
µ
V input offset
voltage simultaneously
•
±
1V to
±
5V operation
BENEFITS
• Eliminates manual and elaborate
system trimming procedures
• Remote controlled automated trimming
• In-System Programming capability
• No external components
• No internal clocking noise source
• Simple and cost effective
• Small package size
• Extremely small total functional
volume size
• Low system implementation cost
• Micropower
APPLICATIONS
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Sensor interface circuits
Transducer biasing circuits
Capacitive and charge integration circuits
Biochemical probe interface
Signal conditioning
Portable instruments
High source impedance electrode
amplifiers
Precision Sample and Hold amplifiers
Precision current to voltage converter
Error correction circuits
Sensor compensation circuits
Precision gain amplifiers
Periodic In-system calibration
System output level shifter
GENERAL DESCRIPTION
The ALD2726E/ALD2726 is a dual monolithic rail-to-rail precision CMOS
operational amplifier with integrated user programmable EPAD (Electri-
cally Programmable Analog Device) based offset voltage adjustment. The
ALD2726E/ALD2726 is a dual version of the ALD1726E/ALD2726 opera-
tional amplifier. Each ALD2721E/ALD2721 operational amplifier features
individual user-programming offset voltage trimming, resulting in signifi-
cantly enhanced total system performance and user flexibility. EPAD
technology is an exclusive ALD design which has been refined for analog
applications where precision voltage trimming is necessary to achieve a
desired performance. It utilizes CMOS FETs as in-circuit elements for
trimming of offset voltage bias characteristics with the aid of a personal
computer under software control. Once programmed, the set parameters
are stored indefinitely within the device even after power-down. EPAD
offers the circuit designer a convenient and cost-effective trimming solution
for achieving the very highest amplifier/system performance.
The ALD2726E/ALD2726 dual operational amplifier features rail-to-rail
input and output voltage ranges, tolerance to over-voltage input spikes of
300mV beyond supply rails, capacitive loading up to 25pF, extremely low
input currents of 0.01pA typical, high open loop voltage gain, useful
bandwidth of 700KHz, slew rate of 0.7V/µs, and low typical supply current
of 50µA for both amplifiers.
ORDERING INFORMATION
Operating Temperature Range
0°C to +70°C
14-Pin
Small Outline
Package (SOIC)
ALD2726ESB
ALD2726SB
0°C to +70°C
14-Pin
Plastic Dip
Package
ALD2726EPB
ALD2726PB
-55°C to +125°C
14-Pin
CERDIP
Package
ALD2726EDB
ALD2726DB
PIN CONFIGURATION
-IN
A
+IN
A
V-
N/C
N/C
+IN
B
-IN
B
1
2
3
4
5
6
7
14
13
12
11
10
9
8
TOP VIEW
SB, PB, DB PACKAGES
VE
2A
VE
1A
OUT
A
V+
OUT
B
VE
1B
VE
2B
* Contact factory for high temperature versions.
* N/C Pins are internally connected. Do not connect externally.
Rev 2.1 ©2011 Advanced Linear Devices, Inc. 415 Tasman Drive, Sunnyvale, CA 94089-1706 Tel: (408) 747-1155 Fax: (408) 747-1286
www.aldinc.com
FUNCTIONAL DESCRIPTION
The ALD2726E/ALD2726 uses EPADs as in-circuit ele-
ments for trimming of offset voltage bias characteristics.
Each ALD2726E/ALD2726 has a pair of EPAD-based cir-
cuits connected such that one circuit is used to adjust V
OS
in
one direction and the other circuit is used to adjust V
OS
in the
other direction. While each of the EPAD devices is a
monotonically adjustable programmable device, the V
OS
of
the ALD2726E can be adjusted many times in both direc-
tions. Once programmed, the set V
OS
levels are stored
permanently, even when the device power is removed.
Functional Description of ALD2726E
The ALD2726E is pre-programmed at the factory under
standard operating conditions for minimum equivalent input
offset voltage. It also has a guaranteed offset voltage
program range, which is ideal for applications that require
electrical offset voltage programming.
The ALD2726E is an operational amplifier that can be
trimmed with user application-specific programming or in-
system programming conditions. User application-specific
circuit programming refers to the situation where the Total
Input Offset Voltage of the ALD2726E can be trimmed with
the actual intended operating conditions.
For example, an application circuit may have +1V and -1V
power supplies, and the operational amplifier input is biased
at +1V, and an average operating temperature at +85
°
C.
The circuit can be wired up to these conditions within an
environmental chamber with the ALD2726E inserted into a
test socket connected to this circuit while it is being electri-
cally trimmed. Any error in V
OS
due to these bias conditions
can be automatically zeroed out. The Total V
OS
error is now
limited only by the adjustable range and the stability of V
OS
,
and the input noise voltage of the operational amplifier.
Therefore, this Total V
OS
error now includes V
OS
as V
OS
is
traditionally specified; plus the V
OS
error contributions from
PSRR, CMRR, TCV
OS
, and noise. Typically this total V
OS
error (V
OST
) is approximately
±35µV
for the ALD2726E.
In-System Programming refers to the condition where the
EPAD adjustment is made after the ALD2726E has been
inserted into a circuit board. In this case, the circuit design
must provide for the ALD2721E to operate in normal mode
and in programming mode. One of the benefits of in-system
programming is that not only is the ALD2726E offset voltage
from operating bias conditions accounted for, any residual
errors introduced by other circuit components, such as
resistor or sensor induced voltage errors, can also be cor-
rected. In this way, the “in-system” circuit output can be
adjusted to a desired level, eliminating the need for another
trimming function.
Functional Description of ALD2726
The ALD2726 is pre-programmed at the factory under stan-
dard operating conditions for minimum equivalent input off-
set voltage. The ALD2726 offers similar programmable
features as the ALD2726E, but with a more limited offset
voltage program range. In is intended for standard opera-
tional amplifier applications, where little or no electrical
porggramming by the user is necessary.
USER PROGRAMMABLE V
OS
FEATURE
Each ALD2726E/ALD2726 has four additional pins, com-
pared to a conventional dual operational amplifier which has
eight pins. These four additional pins are named VE1A,
VE2A for op amp A and VE1B, VE2B for op amp B. Each of
these pins VE1A, VE2A, VE1B, VE2B (represented by VExx)
are connected to a separate, internal offset bias circuit. VExx
pins have initial internal bias voltage values of approximately
1V to 2V. The voltage on these pins can be programmed
using the ALD E100 EPAD Programmer and the appropriate
Adapter Module. The useful programming range of voltages
on VExx pins are 1V to 3V.
VExx pins are programming pins, used during electrical
programming mode to inject charge into the internal EPADs.
Increasing voltage on VE1A/VE1B increases the offset volt-
age whereas increasing voltage on VE2A/VE2B decreases
the offset voltage of op amp A and op amp B, respectively.
The injected charge is then permanently stored. After
programming, VExx pins must be left open in order for these
voltages to remain at the programmed levels.
During programming, voltages on VExx pins are increased
incrementally to program the offset voltage of the operational
amplifier to the desired V
OS
. Note that desired V
OS
can be
any value within the offset voltage programmable ranges,
and can be equal zero, a positive value or a negative value.
This V
OS
value can also be reprogrammed to a different
value at a later time, provided that the useful VE1x or VE2x
programming voltage range has not been exceeded. VExx
pins can also serve as capacitively coupled input pins.
Internally, VE1 and VE2 are programmed and connected
differentially. Temperature drift effects between the two
internal offset bias circuits cancel each other and introduce
less net temperature drift coefficient change than offset
voltage trimming techniques such as offset adjustment with
an external trimmer potentiometer.
While programming, V+, VE1 and VE2 pins may be alter-
nately pulsed with 12V (approximately) pulses generated by
the EPAD Programmer. In-system programming requires
the ALD2726E application circuit to accommodate these
programming pulses. This can be accomplished by adding
resistors at certain appropriate circuit nodes. For more
information, see Application Note AN1700.
ALD2726E/ALD2726
Advanced Linear Devices
2 of 13
PCB Design
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