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08/20/02
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1
ADVANCED ANALOG
HIGH RELIABILITY RADIATION
TOLERANT DC/DC CONVERTERS
L-SERIES
Description
n
Total Dose > 25K Rad(Si)
n
SEE > 37 MeV
.
cm
2
/mg
n
Internal EMI filter; Converter Capable of
meeting MIL-STD-461C CE03 and CS01
n
Low Weight, < 85 grams
n
Magnetically Coupled Feedback
n
16V to 50V DC Input Range
n
Up to 25W Output Power
n
Single and Dual Output Models Include
3.3, 5, 12, 15,
5,
12 and
15V
n
High Efficiency - to 82%
n
-55C to +125C Operating Temperature
Range
n
100M
@ 500VDC Isolation
n
Under-Voltage Lockout
n
Short Circuit and Overload Protection
n
Output Over Voltage Limiter
n
Adjustable Output Voltage
n
External Inhibit
n
1,500,000 Hour MTBF
Features
+ 28V Input, Single/Dual Output
The L-Series of DC/DC converters are radiation toler-
ant, high reliability devices designed for moderate ra-
diation environments such as those encountered by low
earth orbit satellites and launch vehicles. For higher
radiation environments, the G-Series of DC/DC con-
verters is recommended. Features include small size,
low weight and a high tolerance to total ionizing dose,
single event effects and environmental stresses such as
temperature extremes, mechanical shock, and vibration.
All components are fully derated to meet the require-
ments of MIL-STD-975 and MIL-STD-1547 and GSFC
PPL-21 Appendix B. Extensive documentation includ-
ing Radiation Susceptibility, Thermal Analysis, Stress
Analysis and MTBF are available.
The converters incorporate a fixed frequency single for-
ward topology with magnetic feedback and an internal
EMI filter. These converters are capable of meeting the
conducted emissions and conducted susceptibility re-
quirements of MIL-STD-461C without any additional
components. All models include an external inhibit port
and have an adjustable output voltage. They are en-
closed in a hermetic 1.5" x 2.3" x 0.425" steel package
and weigh less than 85 grams. The package utilizes
rugged ceramic feed-through copper core pins and is
sealed using parallel seam welding.
Full environmental screening includes temperature cy-
cling, constant acceleration, fine and gross leak, and
burn-in.
Non-flight versions of the L-Series converters are avail-
able for system development purposes. Variations in
electrical specifications and screening to meet custom
requirements can be accommodated.
Applications
n
Low Earth Orbit Satellites (LEO)
n
Launch Vehicles
PD - 94519A
2
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L-SERIES
The L-Series converters utilize a single-ended for-
ward topology with resonant reset. The nominal
switching frequency is 500kHz. Electrical isolation
and tight output regulation are achieved through the
use of a magnetically coupled feedback. Voltage
feed-forward with duty factor limiting provides high
line rejection and protection against output over volt-
age in the event of an internal control loop failure.
This mechanism limits the maximum output voltage
to approximately 20% over the nominal regardless of
the line voltage.
Circuit Description
An internal EMI filter allows the converter to meet the
conducted emissions requirements of MIL-STD-461C
on the input power leads. A single-stage output filter
reduces the typical output ripple to less than 50mV
peak-to-peak.
Output current is limited under any load fault condi-
tion to approximately 125% of rated. An overload
condition causes the converter output to behave like
a constant current source with the output voltage drop-
ping below nominal. The converter will resume nor-
mal operation when the load current is reduced be-
low the current limit point. This protects the converter
from both overload and short circuit conditions. The
current limit point exhibits a slightly negative tem-
perature coefficient to reduce the possibility of ther-
mal runaway.
An external inhibit port is provided to control con-
verter operation. The converter's operation is inhib-
ited when this pin is pulled low. It is intended to be
driven by an open collector logic device. The pin
may be left open for normal operation and has a
nominal open circuit voltage of 10.5V with respect to
the input return (pin 2).
The output voltage of all models can be adjusted
using a single external resistor.
Design Methodology
The L-Series was developed using a proven con-
servative design methodology which includes se-
lecting radiation tolerance and established reliabil-
ity components and fully derating to the requirements
of MIL-STD-975 and MIL-STD-1547. Heavy derat-
ing of the power MOSFET gate and drain voltages
minimize the possibility of SEGR and SEB. A mag-
netic feedback circuit is utilized instead of opto-cou-
plers to minimize temperature, radiation and aging
sensitivity. PSPICE was used extensively to predict
and optimize circuit performance for both beginning
and end-of-life. Thorough design analyses include
Radiation Susceptibility ( TREE ), Stress, Thermal,
and Reliability ( MTBF ).
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3
L-SERIES
Input voltage range - -0.5Vdc to +60Vdc Input voltage range - 16Vdc to +60Vdc
Output power - Internally limited Input voltage range
1
- 16Vdc to +38Vdc
Lead temperature - +300C for 10 seconds Output power - 0 to Max. Rated
Operating temperature - -55C to +135C Operating temperature
2
- -55C to +125C
Storage temperature - -55C to +135C Operating temperature
1
- -55C to +70C
1
Meets derating per MIL-STD-975
2
For operation at +125C see table note 13
Absolute Maximum Ratings
Recommended Operating Conditions
Electrical Performance Characteristics
For Notes to Specifications, refer to page 5
Limits
Parameter
Group A
Subgroup
Conditions
-55C T
C
+85C
V
IN
= 28V DC 5%, C
L
= 0
unless otherwise specified
Min
Nom
Max
Unit
Input Voltage
18
28
50
V
Output Voltage ( Vout )
M3L2803R3S
M3L2805S
M3L2812S
M3L2815S
M3L2805D
M3L2812D
M3L2815D
M3L2803R3S
M3L2805S
M3L2812S
M3L2815S
M3L2805D
M3L2812D
M3L2815D
1
1
1
1
1
1
1
2,3
2,3
2,3
2,3
2,3
2,3
2,3
I
OUT
= 100% rated load
Note 4
I
OUT
= 100% rated load
Note 4
3.27
4.95
11.88
14.85
4.95
11.88
14.85
3.23
4.90
11.76
14.70
4.90
11.76
14.70
3.30
5.00
12.00
15.00
5.00
12.00
15.00
3.33
5.05
12.12
15.15
5.05
12.12
15.15
3.37
5.10
12.24
15.30
5.10
12.24
15.30
V
V
V
V
V
V
V
V
V
V
V
V
V
V
Output power ( P
OUT
)
M3L2803R3S
All Others
1,2,3
V
IN
= 16, 28, 50 Volts, Note 2
0
0
20
25
W
W
Output current ( I
OUT
)
M3L2803R3S
M3L2805S
M3L2812S
M3L2815S
M3L2805D
M3L2812D
M3L2815D
1,2,3
V
IN
= 16, 28, 50 Volts, Note 2
Either Output, Note 3
Either Output, Note 3
Either Output, Note 3
0
0
0
0
0
0
0
6.06
5.00
2.08
1.67
4.00
1.67
1.33
A
A
A
A
A
A
A
Line regulation ( VR
LINE
)
1,2,3
V
IN
= 16, 28, 50 Volts
I
OUT
= 0, 50%, 100% rated, Note 4
-0.5
0.5
%
Load regulation ( VR
LOAD
)
1,2,3
I
OUT
= 0, 50%, 100% rated, Note 4
V
IN
= 16, 28, 50 Volts
-1.0
1.0
%
Cross regulation ( VR
CROSS
)
M3L2805D
M3L2812D
M3L2815D
1,2,3
V
IN
= 16, 28, 50 Volts
Duals only, Note 5
-5.0
-3.0
-3.0
5.0
3.0
3.0
%
%
%
4
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L-SERIES
Electrical Performance Characteristics
( continued )
For Notes to Specifications, refer to page 5
Limits
Parameter
Group A
Subgroup
Conditions
-55C T
C
+85C
V
IN
= 28V DC 5%, C
L
= 0
unless otherwise specified
Min
Nom
Max
Unit
Input current, no load ( I
IN
)
M3L2803R3S
M3L2805S
M3L2812S
M3L2815S
M3L2805D
M3L2812D
M3L2815D
1,2,3
I
OUT
= 0, Pin 4 open
60
70
70
70
70
100
100
mA
mA
mA
mA
mA
mA
mA
Input current inhibited
1,2,3
Pin 4 shorted to pin 2
8
mA
Output ripple ( V
RIP
)
M3L2803R3S
M3L2805S
M3L2812S
M3L2815S
M3L2805D
M3L2812D
M3L2815D
1,2,3
V
IN
= 16, 28, 50 Volts
I
OUT
= 100% rated load
Notes 4, 6
35
50
70
80
80
80
80
mV p-p
mV p-p
mV p-p
mV p-p
mV p-p
mV p-p
mV p-p
Switching frequency ( F
S
)
1,2,3
Sync. Input (Pin 4) open
425
500
575
KHz
Efficiency ( E
FF
)
M3L2803R3S
M3L2805S
M3L2812S
M3L2815S
M3L2805D
M3L2812D
M3L2815D
1,2,3
I
OUT
= 100% rated load
Note 4
68
75
75
75
75
75
75
75
79
80
81
79
79
80
%
%
%
%
%
%
%
Enable Input ( Inhibit Function )
open circuit voltage
drive current ( sink )
voltage range
1,2,3
Note 1
9.5
-0.5
11.5
500
50
V
A
V
Current Limit Point
Expressed as a percentage
of full rated load current
1,2,3
V
out
= 90% of Nominal, Note 4
105
130
%
Power dissipation, load fault (P
D
)
1,2,3
Short Circuit, Overload, Note 8
14
W
Output response to
step load changes (V
TLD
)
4,5,6
Half Load to/from Full Load, Notes 4,9
-300
300
mV pk
Recovery time,
step load changes (T
TLD
)
4,5,6
Half Load to/from Full Load, Note
4,9,10
200
S
Output response to
step line changes (V
TLN
)
4,5,6
16V to/from 50V
I
OUT
= 100% rated load, Notes 1,4,11
-300
300
mV pk
Recovery Time,
step line changes (T
TLN
)
4,5,6
16V to/from 50V
I
OUT
= 100% rated load, Notes
1,4,10,11
200
S
Turn-on Response
Overshoot (V
OS
)
Turn-on Delay (T
DLY
)
4,5,6
No Load, Full Load
Notes 4,12
2
500
10
mV
mS
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5
L-SERIES
Electrical Performance Characteristics
( continued )
Table I. Electrical Performance Characteristics - notes
1)
Parameter is tested as part of design characterization or after design changes. Thereafter, parameter shall be guaranteed to the
limits specified.
2)
Parameter verified during line and load regulation tests.
3)
Output load current must be distributed such that at least 20% of the total load current is being provided by one of the outputs.
4)
Load current split equally between outputs on dual output models.
5)
Cross regulation is measured with 20% rated load on output under test while changing the load on the other output from 20% to 80%
of rated.
6)
Guaranteed for a D.C. to 20MHz bandwidth. Tested using a 20KHz to 10MHz bandwidth using the circuit shown below.
7)
Capacitive load may be any value from 0 to the maximum limit without compromising dc performance. A capacitive load in excess
of the maximum limit may interfere with the proper operation of the converter's overload protection, causing erratic behavior during
turn-on.
8)
Overload power dissipation is defined as the device power dissipation with the load set such that V
OUT
= 90% of nominal.
9)
Load step transition time
10
Sec.
10)
Recovery time is measured from the initiation of the transient to where V
OUT
has returned to within 1% of
its steady state value.
11)
Line step transition time
100
Sec.
12)
Turn-on delay time from either a step application of input power or a logic low to a logic high transition on the inhibit pin (pin 4) to
the point where V
OUT
= 90% of nominal.
13)
For operation at temperatures between +85C and +125C, derate the maximum output power linearly from 100% to 75%.
Parameter
Group A
Subgroup
Conditions
-55C T
C
+85C
V
IN
= 28V DC 5%, C
L
= 0
unless otherwise specified
Limits
Unit
Capacitive Load (CL)
M3L2803R3S
M3L2805S
M3L2812S
M3L2815S
M3L2805D
M3L2812D
M3L2815D
1
I
OUT
= 100% rated load
No effect on DC performance
Notes 1, 4, 7
Each output on duals
2200
1000
180
120
500
90
60
F
F
F
F
F
F
F
Line Rejection
1
I
OUT
= 100% rated load
DC to 50KHz, Notes 1, 4
40
50
dB
Isolation
1
Input to Output or Any Pin to Case
except pin 3, test @ 500VDC
100
M
Device Weight
85
grams
MTBF
MIL-HDBK-217F2, SF, 35C
1.5 x 10
6
Hours
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