ADA4177-1ARMZ-R7 datasheet(29/33 Pages) AD

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Data Sheet

ADA4177-1/ADA4177-2/ADA4177-4

Rev. E | Page 29 of 33

Figure 95 shows the input and output of a comparator circuit

referenced to ground using the ADA4177-1/ADA4177-2/

ADA4177-4. The supply voltages are ±5 V. The −INx input is

grounded and a positive input is stepped to ±1 V. Both the

positive and negative recovery is approximately 4 µs.

VIN

VOUT

Figure 95. ADA4177-1/ADA4177-2/ADA4177-4 Used as a Comparator with

±5 V Supplies and a ±1 V Input Step, Voltage Follower Configuration

OUTPUT PHASE REVERSAL

Phase reversal is defined as a change in polarity in the amplifier

transfer function. Many op amps exhibit phase reversal when

the voltage applied to the input is greater than the maximum

common-mode voltage. In some instances, this phase reversal

can cause permanent damage to the amplifier. In feedback

loops, it can result in system lockups or equipment damage.

The ADA4177-1/ADA4177-2/ADA4177-4 are immune to phase

reversal problems even at input voltages beyond the power

supply settings.

Figure 96. Output Showing No Phase Reversal in Overvoltage Condition

PROPER PRINTED CIRCUIT BOARD (PCB) LAYOUT

The ADA4177-1/ADA4177-2/ADA4177-4 are high precision

devices. To ensure optimum performance at the PCB level, take

care in the design of the board layout.

To avoid leakage currents, maintain a clean and moisture free

board surface. Coating the surface creates a barrier to moisture

accumulation and reduces parasitic resistance on the board.

Keeping supply traces short and properly bypassing the power

supplies minimizes the power supply disturbances caused by

the output current variation, such as when driving an ac signal

into a heavy load. Connect bypass capacitors as closely as possible

to the device supply pins. Stray capacitances are a concern at the

outputs and the inputs of the amplifier. Keep the signal traces at

least 5 mm from supply lines to minimize coupling.

A variation in temperature across the PCB can cause a mismatch

in the Seebeck voltages at solder joints and other points where

dissimilar metals are in contact, resulting in thermal voltage errors.

To minimize these thermocouple effects, orient resistors so that

heat sources warm both ends equally. Ensure, where possible,

that input signal paths contain matching numbers and types of

components, to match the number and type of thermocouple

junctions. For example, dummy components such as zero value

resistors can be used to match real resistors in the opposite

input path. Place matching components in close proximity to

each other, and orient them in the same manner. Ensure that

leads are of equal length so that thermal conduction is in

equilibrium. Keep heat sources on the PCB as far away from

amplifier input circuitry as is practical.

The use of a ground plane is highly recommended. A ground

plane reduces EMI noise and maintains a constant temperature

across the circuit board.

LONG-TERM DRIFT

The stability of a precision signal path over its lifetime or

between calibration procedures is dependent on the long-term

stability of the analog components in the path, such as op amps,

references, and data converters. To help system designers

predict the long-term drift of circuits that use the ADA4177-1/

ADA4177-2/ADA4177-4, Analog Devices measured the offset

voltage of multiple units for 10,000 hours (more than 13 months)

using a high precision measurement system, including an

ultrastable oil bath. To replicate real-world system performance,

the devices under test (DUTs) were soldered onto an FR4 PCB

using a standard reflow profile (as defined in the JEDEC J-STD-

020D standard), as opposed to testing them in sockets. This

manner of testing is important because expansion and

contraction of the PCB can apply stress to the integrated circuit

(IC) package and contribute to shifts in the offset voltage.

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