AFL120XXS 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 to the user
save for minor differences in idle current. (See specification
table).
than100ns, 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.
Synchronization of Multiple Converters
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 III.
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
Figure III. Preferred Connection for Parallel Operation
1
12
Power
Input
Enable 2
Vin
Rtn
Share
+ Sense
- Sense
Return
Case
AFL
Enable 1
Sync Out
Sync In
+ Vout
7
6
1
Optional
Synchronization
Connection
Share Bus
12
Enable 2
Share
Vin
Rtn
Case
+ Sense
- Sense
Return
+ Vout
AFL
Enable 1
Sync Out
Sync In
to Load
7
6
1
12
Enable 2
Share
Vin
Rtn
Case
+ Sense
- Sense
Return
+ Vout
AFL
Enable 1
Sync Out
Sync In
7
6
(Other Converters)
Parallel Operation-Current and Stress Sharing
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 temperature, the current it
provides to the load will be reduced as compensation for
the temperature induced stress on that device.
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
6
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