LT1461-2.5 Linear Technology, LT1461-2.5 Datasheet - Page 10

• Manufacturer Part Number: LT1461-2.5
• Description: Micropower Precision Low Dropout Series Voltage Reference
• Manufacturer: Linear Technology

APPLICATIONS
LT1461-2.5
The typical performance hysteresis curves are for parts
mounted in a socket and represents the performance of
the parts alone. What is more interesting are parts IR sol-
dered onto a PC board. If the PC board is then temperature
cycled several times from – 40 C to 85 C, the resulting
hysteresis curve is shown in Figure 8. This graph shows
the influence of the PC board stress on the reference.
When the LT1461 is soldered onto a PC board, the output
shifts due to thermal hysteresis. Figure 9 shows the effect
of soldering 40 pieces onto a PC board using standard IR
reflow techniques. The average output voltage shift is
–110ppm. Remeasurement of these parts after 12 days
shows the outputs typically shift back 45ppm toward their
initial value. This second shift is due to the relaxation of
stress incurred during soldering.
10
U
Figure 9. Typical Distribution of Output Voltage Shift After Soldering Onto PC Board
INFORMATION
U
12
11
10
Figure 8. – 40 C to 85 C Hysteresis of 35 Parts Soldered Onto a PC Board
9
8
7
6
5
4
3
2
1
0
– 200
WORST-CASE HYSTERESIS
ON 35 UNITS
–160
W
–120
12
10
8
6
4
2
0
–300
– 80
U
–200
OUTPUT VOLTAGE SHIFT (ppm)
85 C TO 25 C
HYSTERESIS (ppm)
– 40
–100
0
0
The LT1461 is capable of dissipating high power, i.e.,
17.5V • 50mA = 875mW. The SO-8 package has a thermal
resistance of 190 C/W and this dissipation causes a
166 C internal rise producing a junction temperature of
T
thermal shutdown will limit the junction temperature to
around 150 C. This high temperature excursion will cause
the output to shift due to thermal hysteresis. Under these
conditions, a typical output shift is –135ppm, although
this number can be higher. This high dissipation can cause
the 25 C output accuracy to exceed its specified limit. For
best accuracy and precision, the LT1461 junction tem-
perature should not exceed 125 C.
J
100
= 25 C + 166 C = 191 C. What will actually occur is the
40
200
80
1461 F09
300
120
– 40 C TO 25 C
160
1461 F08
200