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AHP270XXS Series

than 100ns, maximum low level of +0.8V and a minimum high

level of +2.0V. The sync output of another converter which

has been designated as the master oscillator provides a

convenient frequency source for this mode of operation.

When external synchronization is not required, the sync in

pin should be left unconnected thereby permitting the

converter to operate at its own internally set frequency.

The sync output signal is a continuous pulse train set at

550

± 50KHz, with a duty cycle of 15 ± 5%. This signal is

referenced to the input return and has been tailored to be

compatible with the AFL sync input port. Transition times

are less than 100ns and the low level output impedance is

less than 50

Ω. This signal is active when the DC input

voltage is within the specified operating range and the

converter is not inhibited. This output has adequate drive

reserve to synchronize at least five additional converters.

A typical synchronization connection option is illustrated in

Figure III.

AHP series operating in the parallel mode is that in addition

to sharing the current, the stress induced by temperature

will also be shared. Thus if one member of a paralleled set

is operating at a higher case temperture, the current it

provides to the load will be reduced as compensation for

the temperature induced stress on that device.

When operating multiple converters, system requirements

often dictate operation of the converters at a common

frequency. To accommodate this requirement, the AHP

series converters provide both a synchronization input and

output.

The sync input port permits synchronization of an AHP

converter to any compatible external frequency source

operating between 500KHz and 700KHz. This input signal

should be referenced to the input return and have a 10% to

90% duty cycle. Compatibility requires transition times less

Figure III. illustrates the preferred connection scheme for

operation of a set of AHP converters with outputs operating

in parallel. Use of this connection permits equal sharing of a

load current exceeding the capacity of an individual AHP

among the members of the set. An important feature of the

Internally, these ports differ slightly in their function. In use,

a low on Enable 1 completely shuts down all circuits in the

converter while a low on Enable 2 shuts down the secondary

side while altering the controller duty cycle to near zero.

Externally, the use of either port is transparent save for

minor differences in idle current. (See specification table).

Synchronization of Multiple Converters

Parallel Operation-Current and Stress Sharing

Figure III. Preferred Connection for Parallel Operation

Optional

Synchronization

Connection

Power

Input

(Other Converters)

Share

Bus

1

6

AHP

7

12

- Sense

Enable 2

+ Vout

Return

+ Sense

Share

Vin

Rtn

Case

Enable 1

Sync Out

Sync In

1

6

7

12

- Sense

Enable 2

+ Vout

Return

+ Sense

Share

Vin

Rtn

Case

Enable 1

Sync Out

Sync In

1

6

7

12

- Sense

Enable 2

+ Vout

Return

+ Sense

Share

Vin

Rtn

Case

Enable 1

Sync Out

Sync In

to Load

AHP

AHP