A
DVANCED
L
INEAR
D
EVICES,
I
NC.
TM
ALD1722E
e
®
EPAD
D
LE
AB
E
N
EPAD® LOW POWER CMOS OPERATIONAL AMPLIFIER
KEY FEATURES
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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
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 25
µ
V input offset
voltage simultaneously
Compatible with industry standard pinout
BENEFITS
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Eliminates manual system trimming
Drive up to 4000pF load capacitance
Remote controlled automated trimming
In-System Programming capable
Industry standard pinout
Rail-to-rail input/output
Input bias current of 0.01pA and
input offset voltage of 25µV
No external components
No internal chopper clocking noise
No chopper dynamic power dissipation
Simple and cost effective
Small package size
Low power
APPLICATIONS
GENERAL DESCRIPTION
The ALD1722E is a monolithic rail-to-rail precision CMOS operational
amplifier with integrated user programmable EPAD (Electrically Program-
mable Analog Device) based offset voltage adjustment. The ALD1722E
is a direct replacement of the ALD1712 operational amplifier, with the
added feature of user-programmable offset voltage trimming resulting in
significantly 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 perfor-
mance.
The ALD1722E operational amplifier features rail-to-rail input and output
voltage ranges, tolerance to over-voltage input spikes of 300mV beyond
supply rails, high capacitive loading up to 4000pF, extremely low input
currents of 0.01pA typical, high open loop voltage gain, useful bandwidth
of 1.5MHz, slew rate of 2.1V/µs, and low supply current of 0.8mA.
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Sensor interface circuits
Unity gain buffer amplifier
Precision analog cable driver
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
Current sources
Periodic In-system calibration
System output level shifter
PIN CONFIGURATION
VE1
1
2
3
4
TOP VIEW
SAL, PAL, DA PACKAGES
* N/C Pin is internally connected. Do not connect externally.
8
2
7
6
5
VE2
V+
OUT
N/C
ORDERING INFORMATION
(“L” suffix denotes lead-free (RoHS))
Operating Temperature Range
0°C to +70°C
8-Pin
Small Outline
Package (SOIC)
ALD1722ESAL
0°C to +70°C
8-Pin
Plastic Dip
Package
ALD1722EPAL
-55°C to +125°C
8-Pin
CERDIP
Package
ALD1722EDA
-IN
+IN
V-
* Contact factory for leaded (non-RoHS) or high temperature versions.
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 ALD1722E uses EPADs as in-circuit elements for trim-
ming of offset voltage bias characteristics. Each ALD1722E
has a pair of EPAD-based circuits 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 program-
mable device, the V
OS
of the ALD1722E can be adjusted
many times in both directions. Once programmed, the set
V
OS
levels are stored permanently, even when the device
power is removed.
The ALD1722E 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 ALD1722E 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 ALD1722E can be trimmed with
the actual intended operating conditions.
For example, an application circuit may have +6V and -2.5V
power supplies, and the operational amplifier input is biased
at +0.7V, and an average operating temperature at 55
°
C.
The circuit can be wired up to these conditions within an
environmental chamber with the ALD1722E 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 term (V
OST
) is approximately
±25µV
for the ALD1722E.
The V
OS
contribution due to PSRR, CMRR, TCV
OS
and
external components can be large for operational amplifiers
without trimming. Therefore the ALD1722E with EPAD trim-
ming is able to provide much improved system performance
by reducing these other sources of error to provide signifi-
cantly reduced V
OST.
In-System Programming refers to the condition where the
EPAD adjustment is made after the ALD1722E has been
inserted into a circuit board. In this case, the circuit design
must provide for the ALD1722E to operate in normal mode
and in programming mode. One of the benefits of in-system
programming is that not only is the ALD1722E 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.
USER PROGRAMMABLE V
OS
FEATURE
Each ALD1722E has two pins named VE1 and VE2 which are
internally connected to an internal offset bias circuit. VE1/
VE2 have initial typical values of 1.6V. The voltage on these
pins can be programmed using the ALD E100 EPAD Pro-
grammer and the appropriate Adapter Module. The useful
programming range of VE1 and VE2 is 1.6V to 3.5V.
VE1 and VE2 pins are programming pins, used during
programming mode to inject charge into the internal EPADs.
Increasing voltage on VE1 decreases the offset voltage
whereas increasing voltage on VE2 increases the offset
voltage of the operational amplifier. The injected charge is
permanently stored and determines the offset voltage of the
operational amplifier. After programming, VE1 and VE2
terminals must be left open to settle on a voltage determined
by internal bias currents.
During programming, the voltages on VE1 or VE2 are in-
creased incrementally to set the offset voltage of the opera-
tional amplifier to the desired Vos. Note that desired Vos can
be any value within the offset voltage programmable ranges,
and can be 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 VE1 or VE2 program-
ming voltage range has not been exceeded. VE1 or VE2 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 ALD1722E 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.
ALD1722E
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