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Advanced Linear Devices

ALD1722E/ALD1722

FUNCTIONAL DESCRIPTION

The ALD1722E/ALD1722 uses EPADs as in-circuit ele-

ments for trimming of offset voltage bias characteristics.

Each ALD1722E/ALD1722 has a pair of EPAD-based cir-

other direction.

Functional Description of ALD1722E

While each of the EPAD devices is a monotonically adjust-

be adjusted many times in both directions. Once pro-

when the device power is removed.

The ALD1722E provides the user with an operational ampli-

fier that can be trimmed with user application-specific pro-

gramming or in-system programming conditions. User appli-

cation-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.

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.

For example, an application circuit may have +6V and -2.5V

power supplies, and the operational amplifier input is biased

at +0.7V, and the average operating temperature is at 55

The circuit can be wired up to these conditions within an

environmental chamber, and the ALD1722E can be inserted

into a test socket connected to this circuit while it is being

error is now limited only by the adjustable range and the

ALD1722E.

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-

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 other trimming com-

ponents.

USER PROGRAMMABLE Vos FEATURE

Each ALD1722E/ALD1722 has two pins named VE1 and

VE2 which are internally connected to an internal offset bias

circuit. VE1/VE2 have initial typical values of 1.6 Volt. The

voltage on these pins can be programmed using the ALD

E100 EPAD Programmer and the appropriate Adapter Mod-

ule. The useful programming range of VE1 and VE2 is 1.6

Volt to 3.5 Volts. VE1 and VE2 pins are programming pins,

used during programming mode. The Programming pin is

used during electrical programming to inject charge into the

internal EPADs. Increases of VE1 decrease the offset volt-

age while increases of VE2 increase 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

increased incrementally to set the offset voltage of the

mable ranges, and can be either zero, a positive value or a

to a different value at a later time, provided that the useful

VE1 or VE2 programming 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/ALD1722 application circuit to accommo-

date these programming pulses. This can be accomplished

by adding resistors at certain appropriate circuit nodes. For

more information, see Application Note AN1700.

Functional Description of ALD1722

The ALD1722 is pre-programmed at the factory under stan-

dard operating conditions for minimum equivalent input off-

set voltage.

The ALD1722 offers similar programmable

features as the ALD1722E, but with more limited offset

voltage program range. It is intended for standard opera-

tional amplifier applications where little or no electrical pro-

gramming by the user is necessary.