Datasheet

LT1460
20
1460fc
1
2
3
4
1460 F19
LONG DIMENSION
2
1
0
0
40
3020
FLEXURE NUMBER
10
1460 F20a
–1
OUTPUT DEVIATION (mV)
FLEXURE NUMBER
1460 F20b
LONG DIMENSION
2
1
0
0
40
302010
–1
OUTPUT DEVIATION (mV)
deform the board a fixed amount as shown in Figure 19.
The flexure #1 represents no displacement, flexure #2 is
concave movement, flexure #3 is relaxation to no displace-
ment and finally, flexure #4 is a convex movement. This
motion is repeated for a number of cycles and the relative
output deviation is noted. The result shown in Figure 20a
is for two LT1460S8-2.5s mounted vertically and Figure
20b is for two LT1460S8-2.5s mounted horizontally. The
parts oriented in Figure 20a impart less stress into the
package because stress is absorbed in the leads. Figures
20a and 20b show the deviation to be between 125µV and
Figure 19. Flexure Numbers
Figure 20b. Two Typical LT1460S8-2.5s, Horizontal
Orientation Without Slots
Figure 20a. Two Typical LT1460S8-2.5s, Vertical
Orientation Without Slots
250µV and implies a 50ppm and 100ppm change respec-
tively. This corresponds to a 13- to 14-bit system and is
not a problem for most 10- to 12-bit systems unless the
system has a calibration. In this case, as with temperature
hysteresis, this low level can be important and even more
careful techniques are required.
The most effective technique to improve PC board stress
is to cut slots in the board around the reference to serve
as a strain relief. These slots can be cut on three sides of
the reference and the leads can exit on the fourth side. This
“tongue” of PC board material can be oriented in the long
direction of the board to further reduce stress transferred
to the reference.
The results of slotting the PC boards of Figures 20a and
20b are shown in Figures 21a and 21b. In this example
the slots can improve the output shift from about 100ppm
to nearly zero.
SLOT
2
1
0
0
40
3020
FLEXURE NUMBER
10
1460 F21a
–1
OUTPUT DEVIATION (mV)
SLOT
2
1
0
0
40
3020
FLEXURE NUMBER
10
1460 F21b
–1
OUTPUT DEVIATION (mV)
Figure 21a. Same Two LT1460S8-2.5s in Figure 16a,
but with Slots
Figure 21b. Same Two LT1460S8-2.5s in Figure 16b,
but with Slots
applications inForMation