DC Solid State Power Controller Module

SENSITRON
SEMICONDUCTOR
SPD40D28
TECHNICAL DATA
DATASHEET 5012, Rev. -
DC Solid State Power Controller Module
Description:
The Solid State Power Controller (SSPC) Module is a 40 Amp microcontroller-based Solid State Relay
designed to be used in hi-rel 28V DC applications. This module has integrated current sensing with no
derating over the full operating temperature range. The module is the electronic equivalent to an
electromechanical circuit breaker with isolated control and status.
Compliant Documents & Standards:
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MIL-STD-1275B, Notice1
Characteristics of 28 Volt DC Electrical Systems in Military Vehicles –
20 April 2004
MIL-STD-704F
Aircraft Electrical Power Characteristics - 12 March 2004
MIL-STD-217F, Notice 2
Reliability Prediction of Electronic Equipment - 28 Feb 1995
Module Features:
Epoxy Shell Construction
Solid State Reliability; Low Weight (20 gms) - High Power Density
Same Pin Out as Industry Standard SSPCs in a Smaller Outline
Extremely Low Power, No Derating Over the Full Temperature Range
Electrical Features:
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•
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•
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28VDC Input: Current Rating of 40A with Very Low Drop; 24mV, typ.
True I2t Protection from 50A to 400A with Nuisance Trip Suppression
Instant Trip Protection (50 µsec typ) for Loads Above 400A
Unlimited Interrupt Capability; Repetitive Fault Handling Capability
Thermal Memory
Internally Generated Isolated Supply to Drive the Switch
Low Bias Supply Current: 20 mA typ @ 5V DC
High Control Circuit Isolation: 750V DC Control to Power Circuit
Soft Turn-On to Reduce EMC Issues
EMI Tolerant
Module Reset with a Low Level Signal; Trip Reset Circuit is Trip-Free
TTL/CMOS Compatible, Optically Isolated, Input and Outputs
Schmitt-Trigger Control Input for Noise Immunity
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SENSITRON
SEMICONDUCTOR
SPD40D28
TECHNICAL DATA
DATASHEET 5012, Rev. Table 1 - Electrical Characteristics (at 25 oC and Vbias = 5.0V DC unless otherwise specified)
Control & Status (TTL/CMOS Compatible)
BIAS (Vcc)
BIAS (Vcc) Current
GATE Status, Load Status Signals
CONTROL Signal
VT+ (Positive-going input threshold voltage)
VT− (Negative-going input threshold voltage)
∆VT Hysteresis (VT+ VT−)
Reset
5.0V DC Nominal, 6.5V DC Absolute Maximum
4.5V to 5.5 VDC
20 mA typ
25 mA, max
Voh=3.7V, min, at Ioh=-20mA
Vol=0.4V, max, at Iol=20mA
2.0V, min, 3.5V, max
1.2V, min, 2.3V, max
0.6V, min, 1.4V, max
Cycle CONTROL Signal
Power
Input Voltage – Continuous
– Transient
Power Dissipation
Current
Max Voltage Drop
Max current without tripping
Trip time
Output Rise Time (turn ON)
Output Fall Time under normal turn-off
Output Fall Time under Fault
Min Load Requirement
0 to 40V DC, 50V DC Absolute Maximum
+600V or –600V Spike (< 10 uS)
< 0.7W typ @ 25A @ 25°C
< 1.75W max @ 40A @ 25°C
< 2.55W max @ 40A @ 100°C
40A Continuous
See Trip Curve
24 mV typ @ 25A, TA = 25 oC
40 mV max @ 40A, TA = 25 oC
60 mV max @ 40A, TA = -55 oC ~ 100 oC
44A DC, min
See Trip Curve
110 µsec typ
110 usec typ
50 usec typ
Nil
Protection
Short Circuit Protection
Instant Trip
Unlimited
800%, min; 1200%, max
Physical Characteristics
Temperature
Operating Temperature
Storage Temperature
TA = -55 °C to +100 °C
TA = -55 °C to +125 °C
Environmental
Altitude
Case Dimensions
Operating Orientation
Weight
MTBF (Estimate: MIL STD 217F)
Up to 30,000 ft
Can be installed in an unpressurized area
1.825”L x 1.25”W x 0.38”H
Any
20 grams typ
1.1 Mhrs at 25°C Full load
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SENSITRON
SEMICONDUCTOR
SPD40D28
TECHNICAL DATA
DATASHEET 5012, Rev. -
Figure 1 - Trip Curve
Figure 2 - Timing Diagram
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SENSITRON
SEMICONDUCTOR
SPD40D28
TECHNICAL DATA
DATASHEET 5012, Rev. Table 2 - Signal Timing – (-55 oC to 100 oC @ LINE = 28V DC)
Parameter
Symbol
CONTROL to GATE Status Delay for Turn On
t0
Turn ON Delay
t1
Load Current Rise Time
t2
Turn ON to LOAD Status Delay
t3
CONTROL to GATE Status Delay for Turn Off
t4
Turn OFF Delay
t5
Load Current Fall Time
t6
Turn OFF to LOAD Delay
t7
Min
50
50
Max
1
200
200
1
1
200
200
1
Units
mS
µS
µS
mS
mS
µS
µS
mS
Note: Current Fall Time from trip dependent on magnitude of overload
Figure 3 - Mechanical Dimensions
Table 3 - Pin Definitions
Pin Number Pin Name
1
BIAS
2
GND
3
GATE Status
4
LOAD Status
5
CONTROL Input
6
LINE
7
--8
PWRGND
9
--10
LOAD
Function
+5V DC Supply
5V Return
Switch Status
Load Current Detection
On/Off Control
+28V DC Supply
No Pin
28V Return
No Pin
Load Connection
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SENSITRON
SEMICONDUCTOR
SPD40D28
TECHNICAL DATA
DATASHEET 5012, Rev. -
Figure 4 - Electrical Block Diagram
Description
Figure 4 shows the block diagram of the SPD40D28. It uses a SN74LVC3G14 device for digital I/O. This TTL
compatible device has a Schmitt-Trigger input to minimize the effects of noise on the input. Its outputs can each
drive more than 10 standard TTL loads. It’s also compatible with CMOS inputs and outputs. The
SN74LVC3G14 is isolated from the remainder of the module circuitry by three optocouplers.
The block labeled “Control & Protection Circuitry” gets power from the DC-DC converter and is referenced to the
output of the SPD40D28. This block contains an amplifier to gain up the voltage developed across the sense
resistor. It also contains a microcontroller with on-board timers, A/D converter, clock generator and independent
watchdog timer. The microcontroller implements a precision I2t protection curve as well as an Instant Trip
function to protect the wiring and to protect itself. It performs all of the functions of multiple analog comparators
and discrete logic in one high-reliability component.
The code programmed in the microcontroller acquires the output of the internal A/D converter, squares the
result and applies it to a simulated RC circuit. It checks the output of the simulated circuit to determine whether
or not to trip (turn off the power Mosfets). Because the microcontroller simulates an analog RC circuit, the
SSPC has ‘thermal memory’. That is, it trips faster if there had been current flowing prior to the overload than if
there hadn’t been current flowing. This behavior imitates thermal circuit breakers and better protects the
application’s wiring since the wiring cannot take as much an overload if current had been flowing prior to the
overload.
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SENSITRON
SEMICONDUCTOR
SPD40D28
TECHNICAL DATA
DATASHEET 5012, Rev. The watchdog timer operates from its own internal clock so a failure of the main clock will not stop the watchdog
timer. The code programmed in the microcontroller will periodically reset the watchdog timer preventing it from
timing out. If the code malfunctions for any reason, the watchdog timer is not reset and it times out. When the
watchdog timer times out, it resets the microcontroller. Since the code is designed to detect levels and not
edges, the output of the module, and therefore the output of the SPD40D28, immediately reflects the command
on its input.
The Power Mosfets used in the SPD40D28 have been selected for very low Rds(on) and results in low voltage
drop and low power dissipation. In most applications, the SPD40D28 will be operated at 50 – 60% of rated
current to provide a safety margin. As can be seen in Table 1, when the SPD40D28 is operated at 25 Amps,
62.5% of rated current, it only dissipates 0.7 Watt at room temperature. No heatsinking is required for this
condition. However, if the SPD40D28 is to be operated at maximum rating and/or at elevated temperatures, the
dissipation can exceed 2.5 watts and heatsinking may be required. Some heatsinking can be accomplished by
adding copper area to the LINE and LOAD pins, a heatsink can be epoxied to the surface of the module or a flat
copper or aluminum heatsink can be sandwiched between the SPD40D28 and the printed circuit board using a
thermal pad to maximize heat transfer. Each application should be evaluated at maximum expected constant
current.
For overloads, no heatsinking is required providing the SPD40D28 is allowed some time to cool down. The
SPD40D28 has sufficient thermal mass that the temperature will rise only a few degrees under the worst-case
overload. Repetitive overloads should be avoided. When the SPD40D28 reports a trip condition, the controller
driving the SPD40D28 should allow no more than four repetitions and then allow a few minutes to cool down
before trying to turn on again.
The SPD40D28 will trip on overloads in the ALWAYS TRIP region shown in Figure 1 and will never trip when in
the NEVER TRIP region. The SPD40D28 can be reset by bringing the CONTROL pin to a logic low. When the
CONTROL pin is brought back to a logic high, the SPD40D28 will turn back on. If the overload is still present,
the SPD40D28 will trip again. Cycling the 5 Volt BIAS power will also reset the SPD40D28. If the CONTROL
pin is at a logic high when the BIAS power is cycled, the SPD40D28 will turn back on when the BIAS power is
re-applied.
Status Outputs
The LOAD and GATE status outputs of the SPD40D28 show whether or not the load is drawing current and
whether or not the SPD40D28 Power Mosfet switch is on. A logic high on the LOAD status output shows that
the load draws < 5% of rated load and a logic low shows that the load draws > 15% of rated current. A load that
draws between 5% and 15% of rated current could result in either a high or low logic level on the LOAD status
output. A logic high on the GATE output indicates that the Power Mosfet switch is on while a logic low indicates
that the switch is off.
As can be seen in Table 4, of the 8 possible states for the combination of CONTROL, LOAD and GATE, only 3
states represent valid SSPC operation. The other 5 states indicate either a failed SSPC or, more likely, a short
to ground or a short to the BIAS supply of one of the logic outputs. By comparing the CONTROL input with the
LOAD and GATE outputs, the user can determine whether or not the load is supposed to be on (GATE),
whether or not it’s drawing current (GATE) and whether or not the LOAD and GATE outputs are valid responses
to the CONTROL input.
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SENSITRON
SEMICONDUCTOR
SPD40D28
TECHNICAL DATA
DATASHEET 5012, Rev. State
1
2
3
4
5
6
7
8
CONTROL
L
L
L
L
H
H
H
H
LOAD
L
L
H
H
L
L
H
H
GATE
L
H
L
H
L
H
L
H
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
Table 4 – CONTROL, LOAD & GATE Truth Table
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 14-gauge wire to handle
40 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 12-gauge wire and for a wire temperature of 105 oC, the chart
requires a 10-gauge wire.
Amendment 1 of MIL-W-5088L has a table for copper wire in a bundle, group or harness with conditions on the
number of wires, percent of total harness capacity, etc. This table shows that a 8-gauge wire is necessary for
200 oC operation, 8 gauge for 150 oC and 6 gauge for 105 oC.
MIL-W-5088L has various figures showing derating for harnesses as a function of the number of current carrying
conductors and for altitude. MIL-W-5088L only specifies wire for DC or RMS AC conditions, not for transient or
overload 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 I2R 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: I2t = constant. Every wire has an I2t rating that’s dependent on the
temperature rise allowed and the diameter of the wire. If the I2t rating of the SSPC or circuit breaker is less than
the I2t rating of the wire, then the SSPC or circuit breaker can protect the wire. The maximum I2t rating for the
SPD40D28 is 19.1 x 103 Amp2-Seconds. Every wire size in the paragraphs above has an I2t rating that exceeds
the SPD40D28 I2t 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
The SPD40D28 may be configured as a high-side or low-side switch and may be used in positive or negative
supply applications. Figure 5 shows the connections as a high-side switch with a positive power supply.
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SENSITRON
SEMICONDUCTOR
SPD40D28
TECHNICAL DATA
DATASHEET 5012, Rev. -
Figure 5 – High-Side Switch, Positive Supply
Figure 6 shows a low-side switch with a negative power supply. Note that the PWRGND pin is now connected
to the LINE pin (see Rise/Fall Time paragraph below for more information on the PWRGND pin).
Figure 6 – Low-Side Switch, Positive Supply
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SENSITRON
SEMICONDUCTOR
SPD40D28
TECHNICAL DATA
DATASHEET 5012, Rev. Figure 7 and Figure 8 show negative supply high-side switch and low-side switch implementations. Again, note
the connection of the PWRGND pin.
Figure 7 – High Side Switch, Negative Supply
Figure 8 – Low Side Switch, Negative Supply
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SENSITRON
SEMICONDUCTOR
SPD40D28
TECHNICAL DATA
DATASHEET 5012, Rev. Rise Time & Fall Time
The rise and fall times of the SPD40D28 is pre-set at the factory for a nominal 100uS with a LINE supply of
28VDC (see Table 2 for min/max limits). The rise and fall times will vary linearly with supply voltage. The
PWRGND pin is used to control the rise and fall times. If the PWRGND pin is left open, the rise and fall times
will be about 50uS. Leaving the PWRGND pin open can be useful when a faster rise or fall time is desirable.
With the PWRGND pin connected as in Figures 5 through 8, the SPD40D28 can turn on into a capacitive load of
700uF, min, 1400uF, typ, without tripping for any power supply voltage within the ratings.
Wiring and Load Inductance
Wiring inductance can cause voltage transients when the SPD40D28 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 10 foot length of wire in free air will cause a transient voltage of about 16 Volts when the
SPD40D28 trips at an Instant Trip level of 400 Amps. At the rated load current of 40 Amps, the voltage transient
will be less than 2 Volts. If longer wire lengths are used, a transient suppressor may be used at the LINE pin
and a power diode may be used at the LOAD pin so that the total voltage between the LINE and LOAD pins is
less than 50 Volts.
When powering inductive loads, the negative voltage transient at the LOAD pin can cause the voltage between
LINE and LOAD to exceed the SPD40D28 rating of 50 Volts and a power diode from the LOAD pin to ground
must be used. The cathode of the power diode is connected to the LOAD pin with the anode connected to
ground. The power diode must be able to carry the load current when the SPD40D28 switches off.
Paralleling
Putting two SPD40D28s in parallel will not double the rating to 80 Amps. Due to differences in the Rds(on) of the
Power Mosfets in the SPD40D28s, the current will not share equally. In addition, there are unit-to-unit
differences in the trip curves so that two SPD40D28s in parallel may possibly trip at 55 Amps. Also, both
SPD40D28s will not trip together; the SPD40D28 carrying the higher current will trip first followed by the other
SPD40D28. Multiple SPD40D28s may be used in parallel as long as these complexities are appreciated.
Board Layout
The current-carrying power circuit should be kept well away from the control circuit and other low-level circuits in
the system. It’s unlikely, but possible, that magnetic coupling could affect the control circuit when turning normal
loads on and off. However, in the case of an overload, the magnetic coupling could be 10 times greater than
with normal loads. Effects of such coupling could cause ‘chattering’ when turning on and off, oscillation, and the
possibility of turning the SPD40D28 back on after an overload. The SPD40D28 is a Trip-Free device. Once
tripped it will not turn back on until reset and commanded on again. Reset is accomplished by bringing the
CONTROL pin low and turning the SPD40D28 back on is accomplished by bringing the CONTROL pin high.
Sufficient magnetic coupling between the current-carrying power circuit and the control circuit can negate the
Trip-Free characteristic.
MIL-STD-704F and MIL-STD-1275B
These standards cover the characteristics of the electrical systems in Military Aircraft and Vehicles. The
SPD40D28 meets all of the requirements of MIL-STD-704F including Normal, Emergency, Abnormal and
Electric Starting conditions with the Ripple, Distortion Factor and Distortion Spectrum defined in the standard.
The SPD40D28 also meets all of the requirements of MIL-STD-1275B including operation with Battery and
Generator, Generator Only and Battery Only for all of the conditions described in the standard including
Cranking, Surges, Spikes and Ripple.
In addition, the SPD40D28 can withstand + 600 V spikes for 10uS. This capability is beyond that required by
the standards cited above.
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SENSITRON
SEMICONDUCTOR
SPD40D28
TECHNICAL DATA
DATASHEET 5012, Rev. -
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