Datasheet

ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/ADR4550 Data Sheet
Rev. B | Page 32 of 37
Boosted Output Current Reference
Figure 84 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 V
OUT
equals the output voltage of the reference; current is
then drawn directly from V
IN
instead of from the reference
itself, allowing increased current drive capability.
10203-056
C
L
C
L
0.1µF
2N7002
AD8663
V
IN
U6
V
OUT
+16V
0.1µF1µF
R1
100Ω
R
L
200Ω
ADR4520/ADR4525/
ADR4530/ADR4533/
ADR4540/ADR4550
V
IN
V
OUT
GND
2 6
4
PART
NUMBER
MINIMUM
C
L
ADR4520,
ADR4525
1.0µF
ADR4530,
ADR4533,
ADR4540,
ADR4550
0.1µF
Figure 85. 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 V
OUT
pin directly to
the load device to maintain maximum output voltage accuracy.
LONG-TERM DRIFT (LTD)
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 over 4,500 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), 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.
Figure 85 shows the LTD of the ADR4520/ADR4525/ADR4530/
ADR4533/ADR4540/ADR4550. The red, blue, and green traces
show sample units. The mean drift after 4,500 hours is 51 ppm.
Note that the early life drift (0 to 250 hours) accounts for 40% of
the total drift observed over 4,500 hours, as shown in Figure 86.
The first 1,000 hours account for 50% of the total drift, and the
remaining 3,500 hours account for the remaining 50% of the drift.
It is clear that the early life drift is the dominant contributor,
while the drift after 1,000 hours is significantly lower.
0 500 1000 1500 2000 2500 3000 3500 4000 4500
TIME (Hours)
–150
–100
–50
0
50
100
150
CHANGE IN OUTPUT VO
LT
AGE (ppm)
MEAN
MEAN PLUS ONE STANDARD DEVIATION
MEAN MINUS ONE STANDARD DEVIATION
SAMPLE 1
SAMPLE 2
SAMPLE 3
V
SY
= 5V
108 UNITS
T
A
= 25°C
10203-797
Figure 86. Measured Long-Term Drift of the ADR4520/ADR4525/ADR4530/
ADR4533/ADR4540/ADR4550 over 4,500 Hours
0 50 100 150 200 250
TIME (Hours)
–50
–40
–30
–20
–10
0
10
20
30
40
50
CHANGE IN OUTPUT VOLTAGE (ppm)
V
SY
= 5V
108 UNITS
T
A
= 25°C
MEAN
MEAN PLUS ONE STANDARD DEVIATION
MEAN MINUS ONE STANDARD DEVIATION
SAMPLE 1
SAMPLE 2
SAMPLE 3
10203-798
Figure 87. Measured Early Life Drift of the ADR4520/ADR4525/ADR4530/
ADR4533/ADR4540/ADR4550
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