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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 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 inches

(Including heat sink if used),P

d

= power dissipation in watts.

The total surface area of the ATR package is 7.34 square

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

sumed, then the case temperature rise of an ATR2805S

can be calculated as follows:

Hence, if T

AMBIENT

= +25

°C, the DC/DC converter case

temperature will be approximately 159

°C if no heat sink

or air flow is provided.

ATR28XXS 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 sys-

tems. Advanced Analog permits synchronization of multiple

ATR28XX converters to match switching frequency of the

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

nating 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

.

.

.

.

.

=

−

















=

−

Output Voltage Adjustment

The output voltage of the ATR2805S converter can be ad-

justed 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

+V o ut

Re turn

Pu ls e W id th

Mo du la tor

Prim a ry

H o us ekeeping

Su pp ly

EM I

Filter

1

10

+ In put

En ab le

Sy nc

Inp ut

Re turn

E rror

Am p &

Re f

+S e ns e

-S e ns e

FB

CS

Driv e

Ca se

6

3

9

8

2