MIL-PRF-19500/477K
temperature of 55ēC, the following steps guide the user in what the printed board copper mounting pad size will need
to be with 1 ounce, 2 ounce, and 3 ounce copper for a 1N5802(US), 1N5804(US), and 1N5806(US). 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 on figure 13 to look up 1 amp (X-axis) and follow up to the TJ =175ēC curve (lower)
for 0.78 watts.
b. Calculate maximum thermal resistance needed (175ēC 55ēC) / 0.78 W = 154ēC/W.
c. Look up thermal resistance of 154ēC/W on Y-axis using a thermal resistance versus copper mounting pad
area plot on one of the three curves on figure 14 for different weights of copper foil and then intersect curve
horizontally to get the 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:
2
2
1) .013 in (0.3302 mm ) for 1 ounce copper foil.
2
2
2) .0080 in (0.2032 mm ) for 2 ounce copper foil.
2
2
3) .0053 in (0.13462 mm ) for 3 ounce copper foil.
e. Add a conservative guard-band to the copper mounting pad size (larger) to keep TJ below 175ēC.
6.5.4 Square-wave application with 1N5802(US) , 1N5804(US), 1N5806(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=125ēC and ambient temperature of 55ēC, the following steps guide the user in what the printed board
copper mounting pad size will need to be with 1 ounce, 2 ounce, and 3 ounce copper.
a. Find size of copper mounting pads on standard FR4 base material 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 on figure 15 to look up IF = 1 A (Y-axis) and follow across to the TJ = 125ēC curve
(middle) for VF = 0.70 V.
d. Calculate power = IF * VF * duty factor = 2 * 0.70 * 0.50 = 0.70 W.
e. Calculate maximum thermal resistance needed (125ēC 55ēC) / 0.70 W = 100ēC/W.
f. Look up thermal resistance of 100ēC/W on the Y-axis using a thermal resistance versus copper mounting pad
area plot on one of the three curves on figure 14 for different weights of copper foil cladding and then intersect
curve horizontally to get 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:
2
2
1) .084 in (2.1336 mm ) for 1 ounce copper foil.
2
2
2) .051 in (1.2954 mm ) for 2 ounce copper foil.
2
2
3) .034 in (0.8636 mm ) for 3 ounce copper foil.
h. A conservative pad guard-band is optional since TJ is only 125ēC. NOTE: Multilayer printed boards or, forced
air cooling will improve performance. Closed confinement of the printed boards or will do the opposite. Use
sound thermal management.
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