LT1461DHS8-2.5 Linear Technology, LT1461DHS8-2.5 Datasheet - Page 12

• Manufacturer Part Number: LT1461DHS8-2.5
• Description: IC REF LDO MICROPWR 2.5V 8SOIC
• Manufacturer: Linear Technology

Specifications of LT1461DHS8-2.5

• Reference Type: Series
• Voltage - Output: 2.5V
• Tolerance: ±0.15%
• Temperature Coefficient: 20ppm/°C
• Voltage - Input: 3 ~ 20 V
• Number Of Channels: 1
• Current - Quiescent: 50µA
• Current - Output: 100mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Cathode: -

APPLICATIO S I FOR ATIO
LT1461
Long-Term Drift
Long-term drift cannot be extrapolated from acceler-
ated high temperature testing. This erroneous technique
gives drift numbers that are wildly optimistic. The only
way long-term drift can be determined is to measure it
over the time interval of interest. The erroneous tech-
nique uses the Arrhenius Equation to derive an accelera-
tion factor from elevated temperature readings. The
equation is:
where: E
To show how absurd this technique is, compare the
LT1461 data. Typical 1000 hour long-term drift at 30 C =
60ppm. The typical 1000 hour long-term drift at 130 C =
120ppm. From the Arrhenius Equation the acceleration
factor is:
The erroneous projected long-term drift is:
For a 2.5V reference, this corresponds to a 0.39 V shift
after 1000 hours. This is pretty hard to determine (read
impossible) if the peak-to-peak output noise is larger than
this number. As a practical matter, one of the best labora-
tory references available is the Fluke 732A and its long-
term drift is 1.5 V/mo. This performance is only available
from the best subsurface zener references utilizing spe-
cialized heater techniques.
The LT1461 long-term drift data was taken with parts that
were soldered onto PC boards similar to a “real world”
application. The boards were then placed into a constant
temperature oven with T
12
120ppm/767 = 0.156ppm/1000 hr
A
A
F
F
K = Boltzmann’s Constant
T2 = Test Condition in Kelvin
T1 = Use Condition Temperature in Kelvin
e
e
A
E
0 0000863
K T
= Activation Energy (Assume 0.7)
A
.
0 7
1
.
1
–
T
1
2
U
303
1
–
403
U
1
A
= 30 C, their outputs were
767
W
U
scanned regularly and measured with an 8.5 digit DVM. As
an additional accuracy check on the DVM, a Fluke 732A
laboratory reference was also scanned. Figure 7 shows the
long-term drift measurement system. The data taken is
shown at the end of the Typical Performance Characteris-
tics section of this data sheet. The long-term drift is the
trend line that asymptotes to a value at 2000 hours. Note
the slope in output shift between 0 hours and 1000 hours
compared to the slope between 1000 hours and 2000
hours. Long-term drift is affected by differential stresses
between the IC and the board material created during
board assembly.
Hysteresis
The hysteresis curves found in the Typical Performance
Characteristics represent the worst-case data taken on 35
typical parts after multiple temperature cycles. As ex-
pected, the parts that are cycled over the wider – 40 C to
125 C temperature range have more hysteresis than those
cycled over lower ranges. Note that the hysteresis coming
from 125 C to 25 C has an influence on the – 40 C to 25 C
hysteresis. The – 40 C to 25 C hysteresis is different
depending on the part’s previous temperature. This is
because not all of the high temperature stress is relieved
during the 25 C measurement.
The typical performance hysteresis curves are for parts
mounted in a socket and represent the performance of the
LABORATORY
PCB1
REFERENCE
FLUKE
PCB2
732A
Figure 7. Long-Term Drift Measurement Setup
PCB3
SCANNER
8.5 DIGIT
DVM
COMPUTER
1461 F07