ALD2724E/ALD2724

Advanced Linear Devices

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FUNCTIONAL DESCRIPTION

The ALD2724E/ALD2724 uses EPADs as in-circuit ele-

ments for trimming of offset voltage bias characteristics.

Each ALD2724E/ALD2724 has a pair of EPAD-based cir-

other direction.

While each of the EPAD devices is a

the ALD2724E can be adjusted many times in both direc-

permanently, even when the device power is removed.

Functional Description of ALD2724E

The ALD2724E 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 ALD2724E 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 ALD2724E can be trimmed with

the actual intended operating conditions.

For example, an application circuit may have +5V and -5V

power supplies, and the operational amplifier input is biased

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

The circuit can be wired up to these conditions within an

environmental chamber with the ALD2724E inserted into a

test socket connected to this circuit while it is being electri-

and the input noise voltage of the operational amplifier.

In-System Programming refers to the condition where the

EPAD adjustment is made after the ALD2724E has been

inserted into a circuit board. In this case, the circuit design

must provide for the ALD2724E to operate in normal mode

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

programming is that not only is the ALD2724E 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 ALD2724

The ALD2724 is pre-programmed at the factory under stan-

dard operating conditions for minimum equivalent input off-

set voltage.

The ALD2724 offers similar programmable

features as the ALD2724E, 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.

Each ALD2724E/ALD2724 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 4V.

VExx pins are programming pins, used during electrical

programming mode to inject charge into the internal EPADs.

Increasing voltage on VE1A/VE1B decreases the offset

voltage whereas increasing voltage on VE2A/VE2B in-

creases 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

any value within the offset voltage programmable ranges,

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

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 ALD2724E 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.