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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 cir-

cuit voltage of the inhibit input is 11.5 ±1 VDC.

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

d

= power dissipation in watts.

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

AMBIENT

= +25

°C, the DC/DC converter case

temperature will be approximately 147

°C if no heat sink

or air flow is provided.

ATR28XXD Block Diagram

Application Information

Inhibit Function

Thermal Management

d

°C)

(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 tempera-

ture 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 fre-

quency 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 Advanced Analog ATR28xx converters provide a syn-

chronizing input permitting synchronization of multiple con-

verters to the frequency of the users system clock, thereby

minimizing this type of noise.

Device Synchronization

3

4

+ V out

Retu rn

P u ls e W idth

M odulator

Prim ary

H ous ek ee pin g

Su pp ly

EM I

F ilte r

1

2

9

10

+In put

En ab le

S y nc

In p ut

Retu rn

FB

CS

Driv e

5

-V out

8

Cas e

E rro r

A m p &

R e f

Reg ulator