AHP2805DXCH Datasheet, PDF (6/11 Pages) International Rectifier – HIGH RELIABILITY HYBRID DC/DC CONVERTERS

AHP28XXD 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).
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 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 500 and 700 KHz. This input signal should
be referenced to the input return and have a 10% to 90%
duty cycle. Compatibility requires transition times less than
100 ns, maximum low level of +0.8 volts and a minimum high
level of +2.0 volts. 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 indicated, the sync in
pin should be left open (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 ±50 KHz, 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 100 ns and the low level output impedance is
less than 50 ohms. This signal is active when the DC input
voltage is within the specified operating range and the
converter is not inhibited. This synch output has adequate
drive reserve to synchronize at least five additional
converters. A typical synchronization connection option is
illustrated in Figure III.
Figure III. Preferred Connection for Parallel Operation
Power
Input
Optional
Synchronization
Connection
1
Vin
Rtn
Case
Enable 1
Sync Out
Sync In
6
AHP
12
Enable 2
Share
Trim
- Output
Return
+ Output
7
1
Vin
Rtn
Case
AHP
Enable 1
Sync Out
Sync In
6
12
Enable 2
Share
Trim
- Output
Return
+ Output
7
Share
Bus
to Negative Load
to Positive Load
1
Vin
Rtn
AHP ^Case
Enable 1
Sync Out
Sync In
6
12
Enable 2
Share
Trim
- Output
Return
+ Output
7
(Other Converters)
Parallel Operation-Current and Stress Sharing
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 current
sharing among the members of a set whose load current
exceeds the capacity of an individual AHP. An important
feature of the 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 temperature, the
current it provides to the load will be reduced as
compensation for the temperature induced stress on that
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