F
EATURES
• –55°C to +85°C operation
• 18 to 40 VDC input
(19 to 40 VDC MTW2805S)
• Fully Isolated
• Optocoupler feedback
• Fixed frequency
• Topology – Push-Pull Forward
• 50 V for up to 50 ms transient protection
• Inhibit function
• Indefinite short circuit protection
• Remote sense on MTW2805S model
• Up to 86% efficiency
DC/DC C
ONVERTERS
28 V
OLT
I
NPUT
MTW SERIES
30 WATT
MODELS
VDC O
UTPUT
SINGLE
5
12
15
DUAL
±12
±15
Size (max.): 2.720 x 1.350 x 0.505 inches (69.09 x 34.29 x 12.83 mm)
See Section B8, case J5, for dimensions.
Weight:
60 grams max.
Screening: Standard or ES. See Section C2 for screening options,
see Section A5 for ordering information.
DESCRIPTION
The MTW Series™ of DC/DC converters offer the high efficiency
and wide input voltage range of switching regulators with the isola-
tion, excellent output regulation, and low output noise typical of
linear regulators without requiring the use of external components.
MTW converters are built using thick-film hybrid technology and are
sealed in metal packages for military, aerospace and other high-reli-
ability applications. Unscreened models are sealed with solder and
are guaranteed to pass a gross leak test (maximum leak rate of 1 x
10
-3
atm.-cc/sec). Environmentally screened models (/ES) are
hermetically sealed with solder and will pass a fine leak and gross
leak test as described in Section C2.
MTW converters use a constant frequency pulse-width modulated
switching regulator design operating in the forward mode with a
clock switching frequency of 240 to 300 kHz. Isolation is achieved
through the use of a transformer in the forward power circuit and an
optocoupler in the feedback control loop. The full load output power
of 30 watts is available over the entire 18 to 40 VDC (19 to 40 VDC
for MTW2805S) input range. On dual output models, up to 90% of
full power is available from either output up to a combined total of 30
watts. Input transients of 50 V to up to 50 ms. duration will not impair
normal operation.
Efficiency is high over the entire input voltage range and from
approximately 25% of full load to full load (see typical efficiency
curves).
MTW converters are provided with indefinite short circuit protection
through the use of current limiting techniques. When the output
current reaches approximately 125% of the full rated load, the
output voltage begins to reduce to protect the converter. The
converter can sustain a true short circuit condition indefinitely.
With temperatures measured at the baseplate, the MTW Series is
rated for full power operation from –55°C to +85°C with the power
derated linearly to 0 at 115°C. The MTW’s flanged case facilitates
removal of heat and provides for mechanically secure mounting.In
applications requiring full power operation, an efficient heat sink
attached to the baseplate is required.
An inhibit is provided to allow power shut-down and start-up from a
logic input. An open circuit on the inhibit pin allows normal operation,
while a connection between the inhibit pin and input common
disables the internal oscillator and shuts down the output. In the
inhibit mode, approximately 1 mA must be sunk from pin the inhibit
pin. An open collector, active low, is required to activate the inhibit
function.
All MTW converters are characterized by close output regulation
over the entire operating range with no minimum power require-
ment. On 12 and 15 VDC output models, typical line regulation is 10
to 20 mv. The MTW2805S model uses external remote sense pins
which monitor the voltage at the load to provide typical regulation in
the 5 to 7 mV range. The voltage sensing circuitry operates in a true
four terminal voltage mode, eliminating the adverse effects of line
resistance voltage drops. The remote sense pins may be left uncon-
nected, but see cautions in on the following pages. For normal oper-
ation, remote sense pins should be connected to their respective
output pins.
The MTW Series offers low noise on both the input and output line.
in the single output converters, two-section L-C filters at both the
input and output limit output ripple voltage and minimize reflected
ripple on the input line. A small value (1000 pF, 500 V) ceramic
capacitor connected between the case and input common pin of the
single volt output models will reduce EMI on the input lines to levels
near those required by MIL-STD-461C’s CE03 standard. In the dual
output converters, single-section L-C filters are used at the input
and outputs. If compliance with MIL-STD-461 is necessary, use of
Interpoint’s FMA-416 EMI filter or FM-704A transient suppressor is
recommended.
B4-9
CRANE [ Crane Aerospace & Electronics. ]
