AFL27006S Datasheet, PDF (6/16 Pages) International Rectifier – HYBRID-HIGH RELIABILITY DC/DC CONVERTER

AFL270XXS Series
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
When operating multiple converters, system requirements
often dictate operation of the converters at a common
frequency. To accommodate this requirement, the AFL
series converters provide both a synchronization input and
output.
The sync input port permits synchronization of an AFL
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
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 ± 5.0%. 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 50Ω. 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 3.
Figure 3. Preferred Connection for Parallel Operation
Power
Input
Optional
Synchronization
Connection
1
Vin
Rtn
Case
Enable 1
Sync Out
Sync In
6
AFL
12
Enable 2
Share
+ Sense
- Sense
Return
+ Vout
7
1
Vin
Rtn
Case
Enable 1
Sync Out
Sync In
6
AFL
12
Enable 2
Share
+ Sense
- Sense
Return
+ Vout
7
Share Bus
1
Vin
Rtn
Case
Enable 1
Sync Out
Sync In
6
AFL
12
Enable 2
Share
+ Sense
- Sense
Return
+ Vout
7
to Load
(Other Converters)
Parallel Operation-Current and Stress Sharing
Figure III. illustrates the preferred connection scheme for
operation of a set of AFL converters with outputs operating
in parallel. Use of this connection permits equal sharing of
a load current exceeding the capacity of an individual AFL
among the members of the set. An important feature of the
AFL 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.
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