MIL-PRF-19500/429N
6.5 Applications data.
6.5.1 Half-sine-wave application with 1N5615-1N5623. For a PCB mounting example with FR4 material where the
full 1 amp IO rating (half-sine-wave) is used at a TJ of +175ēC and ambient temperature of +55ēC, the following steps
guide the user in what the PCB pad size will need to be with 1 ounce, 2 ounce, and 3 ounce Copper for a 1N5615 to
1N5623. For axial-leaded, the lead length for mounting will be .187 inch (4.76 mm) or less from body to entry point
on PCB surface.
a. Use the IO versus Po curve in figure 8 to look up 1 Amp (X-axis) and follow up to the TJ = 175ēC curve (lower)
for 1.04 watts.
b. Calculate maximum thermal resistance needed (175ēC 55ēC) /1.04 W = 115 ēC/W.
c. Look up thermal resistance of 115ēC/W on Y-axis using a thermal resistance versus pad area plot on one of
the three curves in figure 9 for different weights of copper cladding and then intersect curve horizontally to get
answer. These curves assume still air, horizontal position.
d. In this example, the answer is: 1 ounce PCB = .042 in X 0.42 in (1.067 mm X 1.067 mm), 2 ounce PCB = .025
in X .025 in (0.635 mm X 0.635 mm), 3 ounce PCB = .014 in X .014 in (0.356 mm X 0.356 mm) for each pad.
e. Add a conservative guard-band to the pad size (larger) to keep TJ below 175ēC.
6.5.2 Square-wave application with 1N5615-1N5623. For a PCB mounting example with FR4 material to support a
0.5 amp IO square wave switching at a 0.50 duty factor (50 percent duty cycle) at TJ = +125ēC and ambient
temperature of +55ēC, the following steps guide the user in what the PCB pad size will need to be with 1 ounce, 2
ounce, and 3 ounce copper.
a. Find size of copper pads on standard FR4 PCB to support operation at 0.5 amp IO square wave switching at a
0.50 duty factor (50 percent duty cycle) at TJ = +125ēC with TA = +55ēC.
b. Calculate peak IF = 0.5A/0.50 duty factor = 1 amp.
c. Use the VF versus IF curve in figure 10 to look up IF = 1 A (Y-axis) and follow across to the TJ = 125ēC curve
(middle) for VF = 0.96 V.
d. Calculate power = IF * VF * duty factor = 1 x 0.96 x 0.50 = 0.48 W.
e. Calculate maximum thermal resistance needed (125ēC 55ēC) / 0.48 W = 146ēC/W.
f. Look up thermal resistance of 146ēC/W on the Y-axis using a thermal resistance versus pad area plot on one
of the three curves in figure 10 for different weights of copper cladding and then intersect curve horizontally to
get answer. Curves assume still air, horizontal position.
g. Answer: 1 ounce PCB = .02 in X .02 in (0.508 mm X 0.508 mm), 2 ounce PCB = .012 in X .012 in (0.305 mm
X 0.305 mm ), 3 ounce PCB = .008 in X .008 in (0.202 mm X 0.202 mm) for each pad.
h. A conservative pad guard-band is optional since TJ is only 125ēC. NOTE: Multilayer PCB's, forced air cooling,
etc. will improve performance. Closed confinement of the PCB will do the opposite. Please use sound thermal
management.
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