• –55°C to +125°C operation
• 16 to 40 VDC input
• Up to 60 dB attenuation
at 500 kHz.
• Active transient suppression
• Undervoltage lockout
• Inhibit function
• Compliant to
, 28 V
FM-704A EMI FILTER
Size (max): 2.910 x 1.125 x 0.400 inches (73.91 x 28.58 x 10.16 mm)
See Section B8, case K1, for dimensions.
40 grams maximum
Screening: Standard, ES, or 883 (Class H). See Section C2 for screening
options, see Section A5 for ordering information.
Interpoint’s FM-704A™ EMI Filter and Transient Suppression
Module combines EMI filtering and transient protection to handle the
demanding requirements of military, aerospace and industrial appli-
cations. As an EMI filter the FM-704A filter reduces the reflected
ripple current from DC/DC switching converters. As a protection
module, it suppresses input transients on the power bus to protect
the converter and other downstream components.
To keep internal power dissipation to safe operating levels, the input
current should never exceed 2.5 amps at 16 Vin or 1.0 amp at 40
Vin. When the FM-704A filter is used with PWM (Pulse Width
Modulated) converters, I
will vary as Power / V
and 2.5 amps
maximum at 16 Vin will reduce to approximately 1 amp maximum
at 40 Vin. The maximum value allowed may be less than 1 amp as
determined by line transients and the safe operating area of Figure
Figure 9 illustrates the maximum allowed internal dissipation for the
FM-704A filter. To calculate watts dissipated, subtract 40 volts from
the transient (VT) to determine the maximum voltage across the
filter and multiply the result by the current (the filter’s output power,
Pout divided by 40).
W = (V
- 40) x P
For example, with 20 watts output and a transient of 400 volts:
W = (400 - 40) x 20/40 = 180
The curve of Figure 9 shows that 180 W can be dissipated for up to
When used in conjunction with Interpoint converters, the FM-704A
EMI filter reduces reflected input ripple current by a minimum of 60
dB at 500 kHz and 55 dB at 1 MHz (see Figures and Electrical
Characteristics table). This attenuation gives the converter/filter
combination performance exceeding MIL-STD-461C’s CE03 test.
Although the FM-704A filter effectively attenuates the ripple gener-
ated by switching converters, it will not suppress RF applied to its
FM-704A filters are rated to operate from -55°C to +125°C base-
plate temperature. To meet MIL-STD-1275A and MIL-STD-704A
requirements, derate output power linearly from 40 watts at 105°C
to 25 watts at 125°C. See Figure 9.
The inhibit function allows the FM-704A filter to be used as a high-
side switch. When the inhibit terminal (pin 6) is left open or pulled
high, the FM-704A filter is enabled. When the terminal is grounded,
the filter shuts off output power.
A soft start function helps reduce inrush current and start-up over-
shoot when the filter is initially powered or when it is released from
the inhibit mode.
An undervoltage lockout feature shuts off output power when input
voltage falls below a specified level. Refer to Figure 8 for more infor-
To provide protection for itself and converters, the FM-704A filter
blocks transients as required by the following standards:
British Standard BS3G100
Civil Aircraft D0160B
Refer to the Electrical Characteristics table on the following page for
Reverse polarity spikes of up to 100 V will not damage the filter,
however the spikes will not be blocked by the filter.
The case of the filter must be connected to the case of the converter
through a low impedance connection to minimize EMI.
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