MILPRF19500/427P
6.5 Applications data.
6.5.1 Half-sine-wave application with 1N5614 through 1N5622 (US). For a printed board mounting example with
FR4 base material where the full 1 amp IO rating (half-sine-wave) is used at a TJ = 175șC and ambient temperature of
55șC, the following steps guide the user in calculating what the printed board copper mounting pad size needs to be
with 1 ounce, 2 ounce, and 3 ounce copper foil. For axial-leaded, the lead length for mounting will be .187 inch (4.76
mm) or less from body to entry point on printed board surface.
a.
Use the IO versus Po curve on figure 7 to look up 1 A (X-axis) and follow up to the TJ = 175șC curve (lower) for
0.90 watts.
b.
Calculate maximum thermal resistance needed (175șC - 55șC) / 0.90W = 133șC/W.
c.
Locate the thermal resistance of 133șC/W on Y-axis using a thermal resistance versus copper mounting pad
area plot on one of the three curves on figure 8 for different weights of copper foil and then intersect curve
horizontally to get answer. These curves assume still air and horizontal printed board position.
* d.
In this example, the copper mounting pad sizes for the different copper foil weights would be as follows:
1)
.030 x .030 inch (0.76 x 0.76 mm) for 1 ounce copper foil.
2)
.018 X .018 inch (0.46 x 0.46 mm) for 2 ounce copper foil.
3)
.011 X .011 inch (0.28 x 0.28 mm) for 3 ounce copper foil.
e.
Add a conservative guard-band to the copper mounting pad size (larger) to keep TJ > 175șC.
6.5.2 Square-wave application with 1N5614 through 1N5622 (US). For a printed board mounting example with
FR4 base material to support a 0.5 amp IO square wave switching at a 0.50 duty factor (50 percent duty cycle) at
TJ = 125șC and ambient temperature of 55șC, the following steps guide the user in calculating what the printed board
copper mounting pad size needs to be with 1 ounce, 2 ounce, and 3 ounce copper foil.
a.
Locate the size of copper mounting pads on standard FR4 base material to support operation at 0.5 A IO
square wave switching at a 0.50 duty factor (50 percent duty cycle) at TJ = 125șC with TA = 55șC.
Calculate peak IF = 0.5A / 0.50 duty factor = 1 A.
b.
Use the VF versus IF curve on figure 9 to look up IF = 1 A (Y-axis) and follow across to the TJ = 125șC curve
c.
(middle) for VF = 0.70 V.
Calculate power = IF * VF * duty factor = 1 * 0.85 * 0.50 = 0.425 W.
d.
e.
Calculate maximum thermal resistance needed (125șC - 55șC) / 0.425 W = 165șC/W.
f.
Locate the thermal resistance of 165șC/W on the Y-axis using a thermal resistance versus copper mounting
pad area plot on one of the three curves on figure 8 for different weights of copper foil and then intersect curve
horizontally determine the answer. Curves assume still air and horizontal printed board position.
* g.
In this example, the copper mounting pad sizes for the different copper foil weights would be as follows:
1)
.015 x .015 inch (0.38 x 0.38 mm) for 1 ounce copper foil.
2)
.009 x .009 inch (0.23 x 0.23 mm) for 2 ounce copper foil.
3)
.0061 x .0061 inch (0.15 x 0.15 mm) for 3 ounce copper foil.
A conservative pad guard-band is optional since TJ ≥ 125șC. Multilayer printed boards or forced air cooling will
h.
improve performance. Closed confinement of the printed board will do the opposite. Use sound thermal
management.
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