8

LT1460-5

This motion is repeated for a number of cycles and the

relative output deviation is noted. The result shown in

Figure 7a is for two LT1460S8-5s mounted vertically and

Figure 7b is for two LT1460S8-5s mounted horizontally.

The parts oriented in Figure 7a impart less stress into the

package because stress is absorbed in the leads. Figures

7a and 7b show the deviation to be between 250

µV and

500

µV 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 7a and

7b are shown in Figures 8a and 8b. In this example the

slots can improve the output shift from about 100ppm to

nearly zero.

LONG DIMENSION

4

2

0

0

40

30

20

FLEXURE NUMBER

10

1460-5 F07a

–2

FLEXURE NUMBER

1460-5 F07b

LONG DIMENSION

4

2

0

0

40

30

20

10

–2

Figure 7b. Two Typical LT1460S8-5s, Horizontal

Orientation Without Slots

Figure 7a. Two Typical LT1460S8-5s, Vertical

Orientation Without Slots

SLOT

4

2

0

0

40

30

20

FLEXURE NUMBER

10

1460-5 F08a

–2

SLOT

4

2

0

0

40

30

20

FLEXURE NUMBER

10

1460-5 F08b

–2

Figure 8a. Same Two LT1460S8-5s in Figure 7a, but

With Slots

Figure 8b. Same Two LT1460S8-5s in Figure 7b, but

With Slots

Figure 6. Flexure Numbers

1

2

3

4

1460-5 F06