SENSITRON
SEMICONDUCTOR
TECHNICAL DATA
DATASHEET 5019, Rev-
• 221 West Industry Court
Deer Park, NY 11729-4681
Phone (631) 586 7600 Fax (631) 242 9798
•
• World Wide Web - http://www.sensitron.com • E-Mail Address - sales@sensitron.com • Page 10
SPDPXXD270 SERIES
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 an 18 gauge wire is necessary for
200
oC operation, 16-gauge for 150 oC and 14-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
SPDxxD270 is 130 Amp
2-Seconds. Every wire size in the paragraphs above has an I2t rating that exceeds the
SPDPxxD270 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.
Application Connections
Due to the presence of the circuitry that keeps the output at safe voltage when the SPDPxxD270 series are off,
the SPDPxxD270 Series may only be configured as a high-side switch as shown in Figure 3.
Rise Time & Fall Time
The rise and fall times of the SPDPxxD270 are pre-set at the factory for a nominal 600µS rise time and 100µS
fall time with a LINE supply of 270VDC (see Table 1 for min/max limits). The rise and fall times will vary linearly
with supply voltage. The “PWR RTN” pin is used to control the rise and fall times. If the “PWR RTN” pin is left
open, the rise and fall times will be less than 25uS. Leaving the “PWR RTN” pin open can be useful when a
faster rise or fall time is desirable; however, the Output Leakage Sink will not be functional with the “PWR RTN”
pin open.
With the “PWR RTN” pin connected as in Figures 3, the SPDPxxD270, when set for a 10 Amp rating, can turn
on into a capacitive load of 220µF, typ, without tripping for any power supply voltage within the ratings. The
capacitive load capability is proportional to current rating and can be therefore easily calculated for each model
and setting in the SPDPxxD270 Series.
Wiring and Load Inductance
Wiring inductance can cause voltage transients when the SPDPxxD270 is switched off due to an overload.
Generally, these transients are small but must be considered when long wires are used on either the “LINE” or
“LOAD” pins or both. A 30 foot length of wire in free air will cause a transient voltage of about 10 Volts when the
SPDP10D270 trips at an Instant Trip level of 80 Amps. At the rated load current of 10 Amps, the voltage
transient will be less than 1 Volt. If longer wire lengths are used, a transient suppressor may be used at the
“LINE” pin so that the total voltage between the “LINE” and “LOAD” pins is less than 500 Volts.
The
SPDPxxD270V series includes a reverse biased diode from the “LOAD” to “PWR RTN” pins to prevent
damaging transients on the output due to inductive loads.
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