MIL-PRF-19500/590K
6.5 Application data.
6.5.1 Half-sine-wave application for the worst-case (highest voltage) 1N6631. For a PCB mounting with
FR4 material where the full 1.4 Amp IO rating (half-sine wave) is used at a TJ of +150ºC and ambient
temperature of 25ºC as shown on the first page ratings, the following steps guide the user in what the PCB
pad size will need to be with 1 oz, 2 oz, and 3 oz copper. For axial-leaded, the lead length for mounting will
be 0.187 inch (4.76 mm) or less from body to entry point on PCB surface.
a.
between the two lower curves for 2.48 watts.
b.
Calculate maximum thermal resistance needed (150ºC to 25ºC) / 2.48 W = 50ºC/W.
c.
Look up thermal resistance of 50ºC/W on Y-axis using a thermal resistance versus pad area plot on
one of the three curves on figure 9 for different weights of copper cladding and then intersect curve
horizontally to get answer. These curves assume still air, horizontal position.
2
2
2
2
In this example, the answer is: 1 oz PCB = 0.6 in (1.52 mm ), 2 oz PCB = 0.32 in (8.13 mm ), 3 oz PCB
d.
2
2
= 0.21 in (5.33 mm ) for each pad.
Add a conservative guard-band to the pad size (larger) to keep TJ below +150ºC.
e.
6.5.2 Square-wave application with 1N6626 to 1N6631. For a PCB mounting example with FR4 material to
support a 0.7 amp IO square-wave switching at a 0.50 duty factor (50 percent duty cycle) at TJ = +125ºC and ambient
temperature of 55ºC, the following steps guide the user in what the PCB pad size will need to be with 1 oz, 2 oz, and
3 oz copper.
Find size of copper pads on standard FR4 PCB to support operation at 0.7 amp IO square wave switching at
a.
a 0.50 duty factor (50 percent duty cycle) at TJ = 125ºC with TA = 55ºC.
Calculate peak IF = 0.7A / 0.50 duty factor = 1.4 amps.
b.
Use the VF versus IF curve in figure 10 to look up IF = 1.4 A (Y-axis) and follow across to the TJ = 125ºC
c.
curve for VF = 1.42 V.
Calculate power = IF x VF x duty factor = 1.4 x 1.42 x 0.50 = 0.994 watts.
d.
e.
Calculate maximum thermal resistance needed (+125ºC to 55ºC) / 0.994 W = 70ºC/W.
f.
Look up thermal resistance of 70ºC/W on the Y-axis using a thermal resistance versus pad area plot on one
of the three curves on figure 9 for different weights of copper cladding and then intersect curve horizontally
to get answer. Curves assume still air, horizontal position.
2
2
2
2
In this example, the answer is: 1oz PCB = 0.20 in (5.08 mm ), 2oz PCB = 0.11 in (2.79 mm ), 3oz PCB =
g.
2
2
0.08 in (2.03 mm ) for each pad.
A conservative pad guard-band is optional since TJ is only +125ºC. NOTE: Multilayer PCBs, forced air
h.
cooling will improve performance. Closed confinement of the PCB will do the opposite. Please use sound
thermal management.
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