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AHE28XXD 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.

Block Diagram

Application Information

Inhibit Function

EMI Filter

An optional EMI filter (AFC461) will reduce the input ripple

current to levels below the limits imposed by MIL-STD-461

CEO3.

Device Synchronization

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).

To take advantage of this capability, the system designer

must assign one of the converters as the master. Then,

by definition, the remaining converters become slaves

and will operate at the masters’ switching frequency.

The user should be aware that the synchronization

system is fail-safe; that is, the slaves will continue

operating should the master frequency be interrupted for

any reason. The layout must be such that the

synchronization output (pin 9) of the master device is

connected to the synchronization input (pin 9) of each

slave device. It is advisable to keep this run short to

minimize the possibility of radiating the 250KHz switching

frequency.

The appropriate parts must be ordered to utilize this

feature. After selecting the converters required for the

system, a ‘MSTR’ suffix is added for the master converter

part number and a ‘SLV’ suffix is added for slave part

number.

International Rectifier offers an option that provides

synchronization of multiple AHE/ATW converters, thus

eliminating this type of noise.

Typical Synchronization Connection

AHE28xxS

AHE28xxS

AFC461

or

AFV461

AHE28xxS

or Other

Compatable

+ In

+ In

+ In

Case

Case

Case

Return

Return

Return

Return

Return

Return

Output

Output

Output

MSTR

SLV

SLV

+ In

Return

Output

Return

System

Bus

3

4

+Vout

Pulse Width

Modulator

EMI

Filter

1

2

10

+Input

Input

Return

FB

Drive 1

Drive 2

9

Sync

5 -Vout

Regulator

Output

Return

Inhibit

Input

Error Amp

& Reference