F
EATURES
–55° to +125°C operation
16 to 40 VDC input
Fully Isolated
Magnetic feedback
Fixed frequency
Topology – Single Ended Forward
50 V for up to 50 ms
transient protection
• Inhibit and synchronization functions
• Indefinite short circuit protection
• Up to 84% efficiency, 21 watts/in
3
•
•
•
•
•
•
•
DC/DC C
ONVERTERS
28 V
OLT
I
NPUT
MHD SERIES
20 WATT
MODELS
VDC O
UTPUT
SINGLE
5
12
15
18
DUAL
±5
±12
±15
Size (max.): Non-flanged, case H2
2.125 x 1.125 x 0.400 inches (53.98 x 28.58 x 10.16 mm)
Flanged case, K3
2.910 x 1.125 x 0.400 inches (73.91 x 28.58 x 10.16 mm)
See Section B8, cases H2 and K3 for dimensions.
Weight:
52 grams max., flanged 55 grams max.
Screening: Standard, ES, or 883 (Class H). See Section C2 for screening
options, see Section A5 for ordering information.
DESCRIPTION
The MHD Series™ of DC/DC converters offers up to 20 watts of
output power over the full military temperature range with up to 84%
efficiency. Thick-film hybrid techniques provide military/aerospace
reliability levels and optimum miniaturization. The MHD Series
power density rating is up to 21 watts/in
3
.
MHD converters are packaged in hermetically sealed metal cases,
making them ideal for use in military, aerospace and other high reli-
ability applications. Units are available with standard screening,
“ES” screening, or fully compliant SMD versions (see Section C2 for
screening conditions).
S
YNCHRONIZATION
The MHD offers a synchronization feature that allows the designer
to match the switching frequency of the converter to the frequency
of the system clock. In free-run (unsynchronized) mode, the MHD
unit switches at 625 kHz (nominal). In sync mode, the converter will
run at any frequency between 500 kHz and 675 kHz. The sync
control operates with a quasi-TTL signal at any duty cycle between
40% and 60%.
Synchronizing the converter with the system clock allows the
designer to confine switching noise to clock transitions, minimizing
interference and reducing the need for filtering. The sync pin should
be connected to input common pin when not in use.
C
ONVERTER
D
ESIGN
The MHD converters are constant frequency, pulse-width mod-
ulated switching regulators which use a quasi-square wave, single
ended, forward converter design. Tight load regulation (5 mV
typical) is maintained via wide bandwidth magnetic feedback and,
on single output models, through use of remote sense. On dual
output models, the positive output is independently regulated and
the negative output is cross regulated through the use of tightly
coupled magnetics and shunt regulators.
Indefinite short circuit protection and overload protection are
provided by a constant current-limit feature. This protective system
senses current in the converter’s secondary stage and limits it to
approximately 115% of the maximum rated output current.
MHD converters are provided with internal filtering capacitors that
help reduce the need for external components in normal operation.
For systems that require compliance with MIL-STD-461C’s CE03
standard, Interpoint offers filter/transient suppression modules
(including the FMC-461, FMD-461 and FM-704A series filters) which
will result in compliance. Contact your Interpoint representative for
further details.
W
IDE
V
OLTAGE
R
ANGE
The MHD converters are designed to provide full power operation
over a full 16 to 40 VDC voltage range. Operation below 16 volts,
including MIL-STD-704E emergency power conditions is possible
with derated power. Refer to the low line dropout graph (Figure 15)
for details.
I
MPROVED
D
YNAMIC
R
ESPONSE
The MHD feed-forward compensation system provides excellent
dynamic response and noise rejection. Audio rejection is typically 50
dB. The min. to maximum step line transient response is typically
less than 4%.
I
NHIBIT
F
UNCTION
MHD converters provide an inhibit terminal that can be used to
disable internal switching, resulting in no output and very low
quiescent input current. The converter is inhibited when a TTL
compatible low (≤0.8 V) is applied to the inhibit pin. The unit is
enabled when the pin, which is internally connected to a pull-up
resistor, is left unconnected or is connected to an open-collector
gate. The open circuit output voltage associated with the inhibit pin
is 9 to 11 V. In the inhibit mode, a maximum of 8 mA must be sunk
from the inhibit pin.
B2-47
MHD SERIES
20 WATT
ABSOLUTE MAXIMUM RATINGS
Input Voltage
• 16 to 40 V
Output Power
• 15 to 20 watts depending on model
Lead Soldering Temperature (10 sec per lead)
• 300°C
Storage Temperature Range (Case)
• –65°C to +150°C
DC/DC C
ONVERTERS
SYNC AND INHIBIT
Sync (500 to 675 kHz)
• Duty cycle 40% min, 60% max
• Logic low 0.8 V max, 0.0 V min
• Logic high 4.0 V min, 10 V max
• Referenced to input common
• If not used, connect to input common
Inhibit: TTL Open Collector
• Logic low (output disabled)
Logic low voltage
≤0.8
V
Inhibit pin current 8.0 mA max
• Referenced to input common
• Logic high (output enabled)
Open collector
TYPICAL CHARACTERISTICS
Output Voltage Temperature Coefficient
• 100 ppm/°C typical
Input to Output Capacitance
• 50 pF typical
Current Limit
• 115% of full load typical
Isolation
• 100 megohm minimum at 500 V
Audio Rejection
• 50 dB typical
Conversion Frequency
• Free run mode 625 kHz typical
550 kHz. min, 650 kHz max
• External sync range 500 to 675 kHz
Inhibit Pin Voltage (unit enabled)
• 9 to 11 V
RECOMMENDED OPERATING CONDITIONS
Input Voltage Range
• 16 to 40 VDC continuous
• 50 V for up to 50 msec transient
Case Operating Temperature (Tc)
• –55°C to +125°C Full power
• –55°C to +135°C Absolute
Derating Output Power/Current
• Linearly from 100% at 125°C to 0% at 135° C
Electrical Characteristics:25C Tc, 28 VDC Vin, 100% load, free run, unless otherwise specified.
SINGLE OUTPUT MODELS
PARAMETER
OUTPUT VOLTAGE
OUTPUT CURRENT
1
OUTPUT POWER
1
OUTPUT RIPPLE
VOLTAGE
LINE REGULATION
2
LOAD REGULATION
INPUT VOLTAGE
1
NO LOAD TO FULL
INPUT CURRENT
CONDITION
V
IN
= 16 to 40 VDC
V
IN
= 16 to 40 VDC
10 kHz – 2 MHz
Tc = –55°C TO +125°C
Vin = 16 to 40 VDC
Tc = –55°C TO +125°C
NO LOAD TO FULL
Tc = –55°C TO +125°C
CONTINUOUS
TRANSIENT 50 ms
NO LOAD
1
FULL LOAD
INHIBITED
1
10 kHz – 10 MHz
Tc = –55°C TO +125°C
SHORT CIRCUIT
POWER DISSIPATION
RECOVERY
1, 3
50% – 100% – 50%
10% – 100%
100% – 10%
50% – 100% – 50%
10% – 100%
100% – 10%
16 – 40 – 16 VDC
TRANSIENT
5
RECOVERY
4
START-UP
1
DELAY
OVERSHOOT
FULL LOAD
NO LOAD
MHD2805S
MIN
4.95
0
0
—
—
—
—
—
—
16
—
—
—
—
—
76
—
—
—
—
—
—
—
—
—
—
—
—
—
TYP MAX
5.00 5.05
—
3
—
35
50
10
15
5
15
28
—
35
0.70
7
20
78
—
1.4
±200
–400
+350
60
60
200
15
50
90
50
50
50
50
40
50
75
—
8
50
—
10
5
±300
–600
+600
200
600
600
MHD2812S
MIN TYP MAX
11.88 12.00 12.12
0
— 1.67
0
—
—
—
—
—
—
16
—
—
—
—
—
80
—
—
—
—
—
—
—
—
—
—
—
—
—
—
25
40
10
15
5
15
28
—
35
0.87
7
20
83
—
1.4
±250
–600
+500
60
150
250
20
40
90
50
50
50
50
40
50
75
—
8
50
—
10
5
±400
–1000
+750
200
300
500
MHD2815S
MIN TYP MAX
14.85 15.00 15.15
0
— 1.33
0
—
—
—
—
—
—
16
—
—
—
—
—
81
—
—
—
—
—
—
—
—
—
—
—
—
—
—
25
40
10
15
5
15
28
—
35
0.85
7
20
84
—
1.4
±350
–800
+600
60
250
250
20
40
90
50
50
50
50
40
50
75
—
8
50
—
10
5
±500
–1200
+1000
200
500
500
MHD2818S
MIN TYP MAX
17.82 18.00 18.18
0
— 1.11
0
—
—
—
—
—
—
16
—
—
—
—
—
81
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
28
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
20
40
90
50
50
50
50
40
50
75
—
8
50
—
10
5
±600
—
—
200
—
—
±600
300
5
180
—
UNITS
VDC
A
W
mV p
mV
mV
VDC
V
mA
A
mA
mA p-p
%
A
ms
mV pk
INPUT RIPPLE
CURRENT
EFFICIENCY
LOAD FAULT
3
SHORT CIRCUIT TO
FULL LOAD
STEP LOAD RESP.
TRANSIENT
RECOVERY
4
STEP LINE RESP.
µs
±200 ±300
—
300
1.4
0
50
5
50
250
±400 ±500
—
300
1.4
0
120
5
120
600
±500 ±600
—
300
1.4
0
150
5
150
750
mV pk
µs
ms
mV pk
Notes
1. Tc = –55°C to +125°C
2. Operation is limited below 16V (see Figure 15).
3. Indefinite short circuit protection not guaranteed above 125°C case.
4. Recovery time is measured from application of the transient to point at which
Vout is within 1% of final value.
5. Transition time
≥
10 µs.
B2-48
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