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ATR28XXD Series

Connecting the inhibit input (Pin 2) to input common (Pin 10)

will cause the converter to shut down. It is recommended

that the inhibit pin be driven by an open collector device

capable of sinking at least 400µA of current. The open

circuit voltage of the inhibit input is 11.5 ±1.0VDC.

Assuming that there is no forced air flow, the package

temperature rise above ambient (

∆T) may be calculated

using the following expression:

where A = the effective surface area in square inhes

(in-cluding heat sink if used), P

The total surface area of the ATR standard package is

7.34 square inches. If a worse case full load efficiency of

78% is assumed, then the case temperature rise can be

calculated as follows:

Hence, if T

temperature will be approximately 147

°C if no heat sink

or air flow is provided.

Block Diagram

Application Information

Inhibit Function

Thermal Management

∆Τ = 80 A

d

(1)

W

Eff

P

P

OUT

d

5

8

1

78

1

30

1

1

.

=

⎥⎦

⎤

⎢⎣

⎡

−

=

⎥⎦

⎤

⎢⎣

⎡

−

=

and

To calculate the heat sink area required to maintain a

specific case temperature rise, equation (1) may be

manipulated as follows:

PKG

d

HEATSINK

A

P

T

A

−

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡ ∆

=

− 43

1

85

0

80

.

.

As an example, if it is desired to limit the case

temperature rise to a maximum of 50

°C above ambient,

the required effective heat sink area is:

2

43

1

85

0

1

19

34

7

5

8

80

50

in

A

HEATSINK

.

.

)

.

(

.

.

=

−

⎥

⎦

⎤

⎢

⎣

⎡

=

−

EMI Filter

An EMI filter (AFC461), available as an option, will reduce

the input ripple current to levels below the limits imposed by

MIL-STD-461B CEO3.

Whenever multiple DC/DC converters are utilized in a single

system, significant low frequency noise may be generated

due to slight difference in the switching frequencies of the

converters (beat frequency noise). Because of the low

frequency nature of this noise (typically less than 10KHz),

it is difficult to filter out and may interfere with proper operation

of sensitive systems (communications, radar or telemetry).

The International Rectifier ATR28XX converters provide a

synchronizing input permitting synchronization of multiple

converters to the frequency of the users system clock,

thereby minimizing this type of noise.

Device Synchronization

3

4

+Vout

Output

Return

Pulse Width

Modulator

Primary

Housekeeping

Supply

EMI

Filter

1

2

9

10

+Input

Inhibit Input

Sync

Input Return

FB

CS

Drive

5 -Vout

8

Case

Error

Amp &

Ref

Regulator