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ATR28XXS 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 inches

(Including heat sink if used),P

The total surface area of the ATR package is 7.34 square

inches. If a worse case full load efficiency of 76% is

assumed, then the case temperature rise of an ATR2805S

can be calculated as follows:

Hence, if T

case

temperature will be approximately 159

°C if no heat sink

or air flow is provided.

Block Diagram

Application Information

Inhibit Function

Thermal Management

To calculate the heat sink area required to maintain a

specific case temperature rise, the above equation may

be manipulated as follows:

PKG

d

HEATSINK

A

P

T

A

−

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡ ∆

=

− 43

1

85

0

80

.

.

As an example, if a maximum case temperature rise of

50

°C above ambient is required, then the required

effective heat sink area is:

EMI Filter

An Optional EMI filter (AFC461)is available that 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. 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. International Rectifier permits synchronization of

multiple ATR28XX converters to match switching frequency

of the converter to the frequency of the system clock, thus

eliminating this type of noise.

Device Synchronization

W

Eff

P

P

out

5

9

1

76

1

30

1

1

.

=

⎥⎦

⎤

⎢⎣

⎡

−

=

⎥⎦

⎤

⎢⎣

⎡

−

=

()

2

43

1

85

0

9

22

34

7

5

9

80

50

in

A

HEATSINK

.

.

.

.

.

=

−

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

=

−

Output Voltage Adjustment

The output voltage of the ATR2805S converter can be

adjusted upward by connecting an appropriate resistor value

between the Positive Output (Pin 5) and the Positive Sense

(Pin 6) as shown in Table 1 below.

Resistance Pin 5 to 6 (

Ω)

Output Voltage Increase (V)

109

0.1

240

0.2

400

0.3

600

0.4

857

0.5

1200

0.6

Table1 Output adjustment resistor values for ATR2805S

5

4

+Vout

Output

Return

Pulse Width

Modulator

Primary

Housekeeping

Supply

EMI

Filter

1

10

+Input

Inhibit

Input

Sync

Input

Return

Error

Amp &

Ref

+Sense

Sense

Return

FB

CS

Drive

Case

6

3

9

8

2