SENSITRON
SEMICONDUCTOR
TECHNICAL DATA
DATASHEET 5002, Rev B
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SPDPXXD28 SERIES
Table 6 – CONTROL, LOAD & GATE Truth Table
State
CONTROL
LOAD
GATE
Comments
1
L
L
L
SSPC failure or shorted LOAD output to ground
2
L
L
H
SSPC failure
3
L
H
L
Normal OFF condition
4
L
H
H
SSPC failure or shorted GATE output to BIAS supply
5
H
L
L
SSPC failure or shorted GATE output to ground
6
H
L
H
Normal ON condition with load current > 15% rated current
7
H
H
L
Tripped
8
H
H
H
Normal ON condition with load current < 5% rated current
Wire Size
MIL-W-5088L has a chart the shows wire size as a function of wire temperature and current. This chart is for a
single copper wire in free air. For an ambient temperature of 70
oC, the chart allows an 18-gauge wire to handle
25 Amps continuously at a wire temperature of 200
oC – a wire temperature rise of 130 oC. For a wire
temperature limited to 150
oC, the chart requires a 16-gauge wire and for a wire temperature of 105 oC, the chart
requires a 14-gauge wire.
Amendment 1 of MIL-W-5088L has a table for copper wire in a bundle, group or harness with condition on the
number of wires, percent of total harness capacity, etc. This table shows that a 12 gauge wire is necessary for
200
oC operation, 10-gauge for 150 oC and 8-gauge for 105 oC.
MIL-W-5088L has various figures showing derating for harnesses as a function of the number of current carrying
conductors for different altitudes. MIL-W-5088L only specifies wire for DC or RMS AC conditions, not for
transient or overload conditions. MIL-W-5088L and its amendment should be consulted to determine minimum
wire sizes for other currents and conditions.
For transient or overload conditions, the transient or overload happens so quickly that heat is not transferred
from the wire to the surroundings. The heat caused by the I
2R heating of the wire causes the temperature to
rise at a linear rate controlled by the heat capacity of the wire. The equation for this linear rise in temperature,
with respect to time, can be solved as: I
2t = constant. Every wire has an I2t rating that’s dependent on the
temperature rise allowed and the diameter of the wire. If the I
2t rating of the SSPC or circuit breaker is less than
the I
2t rating of the wire, then the SSPC or circuit breaker can protect the wire. The maximum I2t rating for the
SPD2P05D28 is 7.45 x 10
3 Amp2-Seconds. Every wire size in the paragraphs above has an I2t rating that
exceeds the SPDP25D28 I
2t rating for the temperature rises stated. Therefore, to select a wire size, it’s simply a
matter of determining the maximum temperature rise of the application and deciding whether or not the wire will
be in a bundle and use the information above. Similarly, the I
2t ratings for the SPDP12D28 and SPDP05D28
are 1.72 x 10
3 Amp2-Seconds and 300 Amp2-Seconds, respectively.