ADR4520ARZ-R7 datasheet(35/40 Pages) AD

35 / 40 page

Data Sheet

ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/ADR4550

Rev. D | Page 35 of 40

Boosted Output Current Reference

Figure 109 shows a configuration for obtaining higher current

drive capability from the ADR4520/ADR4525/ADR4530/

ADR4533/ADR4540/ADR4550 references without sacrificing

accuracy. The op amp regulates the current flow through the

metal-oxide semiconductor field effect transistor (MOSFET)

until VOUT equals the output voltage of the reference; current is

then drawn directly from VIN instead of from the reference

itself, allowing increased current drive capability.

0.1µF

2N7002

AD8663

VIN

VOUT

+16V

0.1µF

1µF

100Ω

200Ω

ADR4520/ADR4525/

ADR4530/ADR4533/

ADR4540/ADR4550

VIN

VOUT

GND

PART

NUMBER

MINIMUM

ADR4520,

ADR4525

1.0µF

ADR4530,

ADR4533,

ADR4540,

ADR4550

0.1µF

Figure 109. Boosted Output Current Reference

Because the current sourcing capability of this circuit depends only

on the current rating of the MOSFET, the output drive

capability can be adjusted to the application simply by choosing

an appropriate MOSFET. In all cases, tie the VOUT pin directly to

the load device to maintain maximum output voltage accuracy.

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 ADR4520/ADR4525/ADR4530/

ADR4533/ADR4540/ADR4550, Analog Devices measured the

output voltage of multiple units for more than 4500 hours (more

than 6 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), rather than 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.

Figure 110 shows the long-term drift of the ADR4520/

ADR4525/ADR4530/ADR4533/ADR4540/ADR4550. Sample 1,

Sample 2, and Sample 3 plot traces show sample units. The

mean drift after 4500 hours is 51 ppm. Note that the early life

drift (0 hours to 250 hours) accounts for 40% of the total drift

observed over 4500 hours, as shown in Figure 111. The first

1000 hours account for 50% of the total drift, and the remaining

3500 hours account for the remaining 50% of the drift. Thus, the

early life drift is the dominant contributor, whereas the drift

after 1000 hours is significantly lower.

500

1000

1500

2000

2500

3000

3500

4000

4500

TIME (Hours)

–150

–100

–50

100

150

MEAN

MEAN PLUS ONE STANDARD DEVIATION

MEAN MINUS ONE STANDARD DEVI ATION

SAMPLE 1

SAMPLE 2

SAMPLE 3

108 UNITS

TA = 25°C

Figure 110. Measured Long-Term Drift of the ADR4520/ADR4525/ADR4530/

ADR4533/ADR4540/ADR4550 over 4,500 Hours

100

150

200

250

TIME (Hours)

–50

–40

–30

–20

–10

108 UNITS

TA = 25°C

MEAN

MEAN PLUS ONE STANDARD DEVIATION

MEAN MINUS ONE STANDARD DEVI ATION

SAMPLE 1

SAMPLE 2

SAMPLE 3

Figure 111. Measured Early Life Drift of the ADR4520/ADR4525/ADR4530/

ADR4533/ADR4540/ADR4550

TIME (HOURS)

–40

1000

2000

3000

4000

5000

–30

–20

–10

54 UNITS

TA = 25°C

MEAN

MEAN PLUS ONE STANDARD DEVI ATION

MEAN MINUS ONE STANDARD DEVI ATION

SAMPLE 1

SAMPLE 2

SAMPLE 3

Figure 112. Measured Long-Term Drift of the ADR4525D/ADR4540D/

ADR4550D over 4,500 Hours

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