B3-3

DESCRIPTION

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.

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

input terminals.

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.

To provide protection for itself and converters, the FM-704A filter

blocks transients as required by the following standards:

MIL-STD-704A

Panavia SP-P-90001

MIL-STD-461B&C

British Standard BS3G100

MIL-STD-1275

Civil Aircraft D0160B

Refer to the Electrical Characteristics table on the following page for

more information.

Reverse polarity spikes of up to 100 V will not damage the filter,

however the spikes will not be blocked by the filter.

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

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

9.

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).

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

4 milliseconds.

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-

mation.

The case of the filter must be connected to the case of the converter

through a low impedance connection to minimize EMI.

FM-704A EMI FILTER

40 WATT

• –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

MIL-STD-461C, CE03

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.

Weight:

40 grams maximum

Screening:

Standard, ES, or 883 (Class H). See Section C2 for screening

options, see Section A5 for ordering information.

MODEL

FM-704A

40 Watts