SPDPXXD28_09 datasheet(9/14 Pages) SENSITRON

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SENSITRON

SEMICONDUCTOR

TECHNICAL DATA

DATASHEET 5023, Rev D.1

• 221 West Industry Court • Deer Park, NY 11729-4681

Phone (631) 586 7600 Fax (631) 242 9798

• www.sensitron.com • sales@sensitron.com • Page 9

SPDPXXD28 SERIES

whether or not it’s drawing current (GATE) and whether or not the LOAD and GATE outputs are valid responses

to the CONTROL input.

Table 6 – CONTROL, LOAD & GATE Truth Table

State

CONTROL

LOAD

GATE

Comments

SSPC failure or shorted LOAD output to ground

SSPC failure

Normal OFF condition

SSPC failure or shorted GATE output to BIAS supply

SSPC failure or shorted GATE output to ground

Normal ON condition with load current > 15% rated current

Tripped

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.

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