LT1461-2.5 Linear Technology, LT1461-2.5 Datasheet - Page 8

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

APPLICATIONS
LT1461-2.5
or a region where the flexure of the board is minimum. The
package should always be mounted so that the leads
absorb the stress and not the package. The package is
generally aligned with the leads parallel to the long side of
the PC board as shown in Figure 5a.
A qualitative technique to evaluate the effect of stress on
voltage references is to solder the part into a PC board and
deform the board a fixed amount as shown in Figure 4. The
flexure #1 represents no displacement, flexure #2 is
concave movement, flexure #3 is relaxation to no dis-
placement and finally, flexure #4 is a convex movement.
8
–1
–1
1
0
1
0
2
2
0
0
Figure 5a. Two Typical LT1461S8-2.5s,
Vertical Orientation Without Slots
Figure 5b. Two Typical LT1461S8-2.5s,
Horizontal Orientation Without Slots
1
2
3
4
10
10
Figure 4. Flexure Numbers
U
INFORMATION
FLEXURE NUMBER
FLEXURE NUMBER
U
LONG DIMENSION
LONG DIMENSION
20
20
W
1461 F04
30
30
U
1461 F05a
1461 F05b
40
40
This motion is repeated for a number of cycles and the
relative output deviation is noted. The result shown in
Figure 5a is for two LT1461S8-2.5s mounted vertically
and Figure 5b is for two LT1461S8-2.5s mounted horizon-
tally. The parts oriented in Figure 5a impart less stress into
the package because stress is absorbed in the leads.
Figures 5a and 5b show the deviation to be between 125 V
and 250 V and implies a 50ppm and 100ppm change
respectively. 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 tempera-
ture 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.
Figure 6a. Same Two LT1461S8-2.5s in Figure 5a, but with Slots
Figure 6b. Same Two LT1461S8-2.5s in Figure 5b, but with Slots
–1
–1
2
1
0
2
1
0
0
0
10
10
FLEXURE NUMBER
FLEXURE NUMBER
20
20
SLOT
SLOT
30
30
1461 F06a
1461 F06b
40
40