Datasheet LT1236LS8 (Analog Devices) - 9

LT1236LS8
applicaTions inForMaTion Hysteresis
stresses on the die have changed position. This shift is Thermal hysteresis is a measure of change of output volt- similar, but more extreme than thermal hysteresis. age as a result of temperature cycling. Figure 2a and 2b Experimental results of IR reflow shift are shown below illustrate the typical hysteresis based on data taken from in Figure 4. These results show only shift due to reflow the LT1236LS8. A proprietary design technique minimizes and not mechanical stress. thermal hysteresis. 300 380s
IR Reflow Shift
TP = 260°C RAMP DOWN The mechanical stress of soldering a part to a board can 225 TL = 217°C TS(MAX) = 200°C cause the output voltage to shift. Moreover, the heat of t T P S = 190°C 30s an IR reflow or convection soldering oven can also cause TURE (°C) 150 T = 150°C the output voltage to shift. The materials that make up a tL RAMP TO semiconductor device and its package have different rates 130s TEMPERA 150°C of expansion and contraction. After a part undergoes the 75 40s extreme heat of a lead-free IR reflow profile, like the one 120s shown in Figure 3, the output voltage shifts. After the 0 device expands, due to the heat, and then contracts, the 0 2 4 6 8 10 MINUTES 1236ls8 F03 22
Figure 3. Lead-Free Reflow Profile
25°C TO 0°C TO 25°C 20 25°C TO 70°C TO 25°C 18 10 16 1× REFLOW 9 3× REFLOW 14 24Hr REST 8 12 7 10 8 6 NUMBER OF UNITS 6 5 4 4 2 NUMBER OF UNITS 3 0 2 –50 –30 –10 10 30 50 70 90 DISTRIBUTION (ppm) 1 1236ls8 F02a 0
Figure 2a. Hysteresis Plot 0°C to 70°C
–0.05 –0.04 –0.03 –0.02 –0.01 0 0.01 REFLOW SHIFT (%) 1236ls8 F04 35 25°C TO –40°C TO 25°C
Figure 4. Output Voltage Shift Due to IR Reflow
25°C TO 85°C TO 25°C 30
Humidity Sensitivity
25 Plastic mold compounds absorb moisture. With changes 20 in relative humidity, plastic packaging materials change 15 the amount of pressure they apply to the die inside, which NUMBER OF UNITS can cause slight changes in the output of a voltage refer- 10 ence, usually on the order of 100ppm. The LS8 package is 5 hermetic, so it is not affected by humidity, and is therefore 0 more stable in environments where humidity may be a –120 –80 –40 0 40 80 120 concern. However, PC Board material may absorb moisture DISTRIBUTION (ppm) 1236ls8 F02b and apply mechanical stress to the LT1236LS8. Proper
Figure 2b. Hysteresis Plot –40°C to 85°C
board materials and layout are essential. 1236ls8f 9 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Typical Applications Package Description Typical Application Related Parts