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Advanced Linear Devices

ALD2726E/ALD2726

Functional Description of ALD2726

The ALD2726 is pre-programmed at the factory under

standard operating conditions for minimum equivalent input

offset voltage.

The ALD2726 offers similar programmable

features as the ALD2726E, but with more limited offset

voltage program range. It is intended for standard

operational amplifier applications where little or no electrical

programming by the user is necessary.

Each ALD2726E/ALD2726

has four additional pins,

compared 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

1 to 2 Volts. 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 1 Volt to 3 Volts.

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 pro-

gramming, 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

any value within the offset voltage programmable ranges,

and can be either equal zero, a positive value or a negative

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 ALD2721E 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.

FUNCTIONAL DESCRIPTION

The ALD2726E/ALD2726 utilizes EPADs as in-circuit

elements for trimming of offset voltage bias characteristics.

Each ALD2726E/ALD2726 operational amplifier has a pair of

EPAD-based circuits connected such that one circuit is used to

ALD2721E can be adjusted many times in both directions.

even when the device 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

stand-alone, with user application-specific programming or in-

system programming conditions. User application-specific

circuit programming refers to a situation where the Total Input

Offset Voltage of the ALD2726E can be trimmed with the actual

intended operating conditions.

Take the example of an application circuit that uses + 1V and

-1V power supplies, an operational amplifier input biased at

+1V, and an average operating temperature at +85

°C; the

circuit can be wired up to these conditions within an environ-

mental chamber with the ALD2726E inserted into a test socket

these bias conditions can be automatically zeroed out. 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 ALD2726E to operate in both normal mode and

in programming mode. One of the benefits of in-system

programming is that not only the ALD276E offset voltage from

operating bias conditions has been accounted for, any residual

errors introduced by other circuit components, such as resistor

or sensor induced voltage errors, can also be programmed and

corrected. In this way, the “in-system” circuit output can be

adjusted to a desired level eliminating need for another

trimming function.